fighting reversion
10-29-06, 05:56 PM
#1
fighting reversion
I've searched, and this subject has been covered before. However my specific questions haven't.
What I'd like to pick your brains about is why Mazda started out with short primary ports on the outside of the intermediate plates, and then made them tall some time in the mid '70s and kept them that way up to the '85 12A. Interestingly, the engine ports were made taller but the manifold ports stayed the same size, as well as the port timing on the inside of the engine, for the most part.
The common consensus is this port mismatch fights the reversion wave as the rotor passes by the port before it closes. Additionally, Paul Yaw recommends against port matching the intake manifold because it kills velocity and flow. http://www.yawpower.com/Flow%20Testing.html (scroll down part way to #1)
I have several intermediate plates with short and tall ports from which to chose. My goal is to build a couple torquey carbed NA 4 port 13Bs for my REPU and baja.
The REPU engine has true '74 3B castings and rotor housings with the MAZDA font above the dowel pins. The intermediate ports are short on the outside and tallish on the inside. They close 10° later than all '76-'85 12As and '76-'83 (carbed) 13Bs. I refer to them simply as '74 spec ports.
The baja engine will have 1st gen Y side plates and J-spec rotor housings. The intake port timing will stay stock but I'll smooth out the harsh 90° edges and any casting flash inside, leaving a rough surface to help with fuel-wetting issues during stabs of the throttle. The J-spec exhaust ports open 10° later than US-spec from the same era (thermal reactors) and close at T2 spec but are narrower and have less total duration than T2. They look like '70s US spec but a little taller and further up the rotor housing.
Here is the Paul Yaw article where he explains how to get good low RPM torque out of a rotary. http://www.yawpower.com/febtech.html (scroll down to [purple]Low RPM Operation[/purple] It seems to me my J-spec rotor housings fulfill at least on the of the goals rather nicely (opening later). The other goals, such as smaller crossectional area, is true compared to T2 ports, but knowing US-spec ports in the '70s and early '80s were grossly restrictive suggests that my ports are probably right on the money as is. There won't be any room for a long primary exhaust though. Unless... I'll have to look into it later.
Both engines will use nearly stock 13B Hitachi carbs (changed air bleeds and jets) which work very well for driveability and provide acceptable power on stock or '74 spec ports.
Now that the background info is out of the way, here are the questions.
REPU:
Should I use the 3B short port intermediate plate on the '74 REPU engine? Or should I swap in a tall port 1st gen Y plate ported to '74 spec? I've had excellent results on several engines ported to '74 spec with this type of intermediate plate. I suspect the tall ports fight the reversion wave and improve low end power. Another thing to consider is the '74 REPU had very short diff gearing of 4.625 allowing for a less torquey engine to be used, and the '74 spec ports allowed better mid to high range and performance along with small US-spec exhaust ports and a heavy stock fywheel. They were the pickup with pick up!
Baja:
The J-spec doner engine had short ports on the outside and even smaller ports on the inside. If you've ever compared FC primary ports to a 12A, you'd see the port timing of the 12A had a lot more duration than the 13B. You must also realise that the 13B was flowing through four ports at low RPM with additional auxiliary ports opening at higher RPM. The 12A only had primaries and secondaries with channels connecting up under the carb spacer. My J-spec manifold also has these channels (nice!). Anyway the J-spec intermediate plate's port timing is identical to an FC but the secondaries were identical to a 12A. Total flow is less than either engine. What's going on?
Back to the '74 engine. At the moment I'm thinking I should go with a Y plate and maybe enlarge the exhaust ports a little bit. It would be a nice tradeoff because while it will gain some low RPM torque with the reduction in reversion, some torque will be taken away due to the larger exhaust ports, but they'll flow better at higher RPM. So perhaps little may be gained down low but I expect an improvement in the upper RPM range. In total the engine will have more power but the low end may stay the same. I somehow don't think the rear diff will care either way.
The baja however needs as much low end as possible. The high end is less important. To get back to what I was talking about earlier, the J-spec intermediate plate had short ports all the way through. While these may have worked on the stock setup with its channeled manifold, its tiny jets (90/140) and huge air bleeds (90/160) on an automatic (came with a counterweight woohoo!) and the points-friendly B6ET (very hot) plugs, not to mention its 190°F thermostat (too hot for me) in a Luce or some other luxury car lazed about town, I somehow very highly doubt it's going to be a good setup for the baja... unless I change things around.
It's a given this thing will get electronic ignition and DLIDFIS with the directly fired FC plugs in leading and the BR8EQ-14 plugs in trailing firing through the cap. The carb will have bigger jets (100/145 or more) and much, much smaller air bleeds (60/90) for better low RPM but much improved high RPM peformance. Of course when I say high RPM, in a VW, that's anything over 4500. Oh, and a 180°F thermostat, at least.
I'm going to keep the channeled manifold because I've found they work extremely well compared to stock manifolds from this era when used with tall port primaries. My '74 engine's manifold will also get cut. If you guys don't know what I'm talking about, next time you get a chance to look at a '79 manifold without the carb or spacer attatched, check out the shallow channels connecting primary runners to secondary runners. I assume the vacuum signal the carb sees is strengthened in these models. I doubt much actual flow between them takes place. If you have an unchanneld one from the '70s, it is a fairly easy task to cut channels in them too. I did one and it idled down to 600RPM within seconds of its first time firing up right after a rebuild. It was very smooth and responded extremely well to accelerator pump/throttle jabs. The fuel-wetting issue is appearantly a non-issue with these. Even in a stone cold manifold!
Oh yeah, no choke (hence the low idle). Oh, and did I forget to mention this engine had some extremely huge streetports? Low end torque may not be that great, but the idle makes me think otherwise. We'll see (it's going into my GLC).
If you guys were able to follow along with my post, good for you. I know there's a lot of reading and this subject may only interest the diehards around here. But if you know anything about port size and why Mazda went to tall ports and channeled manifolds for their carbed vehicles some time in the '70s and kept it basically that way through the early '80s, I'd appreciate your input. Which is ultimately better anyway? Is it a potential catch22 like the crappy '81-'85 12A manifolds? Of course newer isn't always better, but what can I combine; new and old, to make it work for me?
Ok back to the baja. I'm leaning toward a Y intermediate to take advantage of the tall ports and less reversion. Should I keep it at 12A port timing? Or go with '74 spec ports? Again, high RPM isn't super important because 4500 is considered high for this thing. Maybe up to 6000 would be fine. The tranny is from a bug with tall gears and the current air cooled VW has a hard time motivating it; you have to wind out 1st gear almost to the 4000 RPM redline just to go into 2nd and have any chance at continuing to accelerate at a decent pace. Hence the need for more low end torque and a high rev limit, but not destructive torque potential like it would be if I went with a V6 or type 4 etc. Let me know what you think.
I'll post pics if it'll make these concepts easier to visualize.
What I'd like to pick your brains about is why Mazda started out with short primary ports on the outside of the intermediate plates, and then made them tall some time in the mid '70s and kept them that way up to the '85 12A. Interestingly, the engine ports were made taller but the manifold ports stayed the same size, as well as the port timing on the inside of the engine, for the most part.
The common consensus is this port mismatch fights the reversion wave as the rotor passes by the port before it closes. Additionally, Paul Yaw recommends against port matching the intake manifold because it kills velocity and flow. http://www.yawpower.com/Flow%20Testing.html (scroll down part way to #1)
I have several intermediate plates with short and tall ports from which to chose. My goal is to build a couple torquey carbed NA 4 port 13Bs for my REPU and baja.
The REPU engine has true '74 3B castings and rotor housings with the MAZDA font above the dowel pins. The intermediate ports are short on the outside and tallish on the inside. They close 10° later than all '76-'85 12As and '76-'83 (carbed) 13Bs. I refer to them simply as '74 spec ports.
The baja engine will have 1st gen Y side plates and J-spec rotor housings. The intake port timing will stay stock but I'll smooth out the harsh 90° edges and any casting flash inside, leaving a rough surface to help with fuel-wetting issues during stabs of the throttle. The J-spec exhaust ports open 10° later than US-spec from the same era (thermal reactors) and close at T2 spec but are narrower and have less total duration than T2. They look like '70s US spec but a little taller and further up the rotor housing.
Here is the Paul Yaw article where he explains how to get good low RPM torque out of a rotary. http://www.yawpower.com/febtech.html (scroll down to [purple]Low RPM Operation[/purple] It seems to me my J-spec rotor housings fulfill at least on the of the goals rather nicely (opening later). The other goals, such as smaller crossectional area, is true compared to T2 ports, but knowing US-spec ports in the '70s and early '80s were grossly restrictive suggests that my ports are probably right on the money as is. There won't be any room for a long primary exhaust though. Unless... I'll have to look into it later.
Both engines will use nearly stock 13B Hitachi carbs (changed air bleeds and jets) which work very well for driveability and provide acceptable power on stock or '74 spec ports.
Now that the background info is out of the way, here are the questions.
REPU:
Should I use the 3B short port intermediate plate on the '74 REPU engine? Or should I swap in a tall port 1st gen Y plate ported to '74 spec? I've had excellent results on several engines ported to '74 spec with this type of intermediate plate. I suspect the tall ports fight the reversion wave and improve low end power. Another thing to consider is the '74 REPU had very short diff gearing of 4.625 allowing for a less torquey engine to be used, and the '74 spec ports allowed better mid to high range and performance along with small US-spec exhaust ports and a heavy stock fywheel. They were the pickup with pick up!
Baja:
The J-spec doner engine had short ports on the outside and even smaller ports on the inside. If you've ever compared FC primary ports to a 12A, you'd see the port timing of the 12A had a lot more duration than the 13B. You must also realise that the 13B was flowing through four ports at low RPM with additional auxiliary ports opening at higher RPM. The 12A only had primaries and secondaries with channels connecting up under the carb spacer. My J-spec manifold also has these channels (nice!). Anyway the J-spec intermediate plate's port timing is identical to an FC but the secondaries were identical to a 12A. Total flow is less than either engine. What's going on?
Back to the '74 engine. At the moment I'm thinking I should go with a Y plate and maybe enlarge the exhaust ports a little bit. It would be a nice tradeoff because while it will gain some low RPM torque with the reduction in reversion, some torque will be taken away due to the larger exhaust ports, but they'll flow better at higher RPM. So perhaps little may be gained down low but I expect an improvement in the upper RPM range. In total the engine will have more power but the low end may stay the same. I somehow don't think the rear diff will care either way.
The baja however needs as much low end as possible. The high end is less important. To get back to what I was talking about earlier, the J-spec intermediate plate had short ports all the way through. While these may have worked on the stock setup with its channeled manifold, its tiny jets (90/140) and huge air bleeds (90/160) on an automatic (came with a counterweight woohoo!) and the points-friendly B6ET (very hot) plugs, not to mention its 190°F thermostat (too hot for me) in a Luce or some other luxury car lazed about town, I somehow very highly doubt it's going to be a good setup for the baja... unless I change things around.
It's a given this thing will get electronic ignition and DLIDFIS with the directly fired FC plugs in leading and the BR8EQ-14 plugs in trailing firing through the cap. The carb will have bigger jets (100/145 or more) and much, much smaller air bleeds (60/90) for better low RPM but much improved high RPM peformance. Of course when I say high RPM, in a VW, that's anything over 4500.
Oh, and a 180°F thermostat, at least.I'm going to keep the channeled manifold because I've found they work extremely well compared to stock manifolds from this era when used with tall port primaries. My '74 engine's manifold will also get cut. If you guys don't know what I'm talking about, next time you get a chance to look at a '79 manifold without the carb or spacer attatched, check out the shallow channels connecting primary runners to secondary runners. I assume the vacuum signal the carb sees is strengthened in these models. I doubt much actual flow between them takes place. If you have an unchanneld one from the '70s, it is a fairly easy task to cut channels in them too. I did one and it idled down to 600RPM within seconds of its first time firing up right after a rebuild. It was very smooth and responded extremely well to accelerator pump/throttle jabs. The fuel-wetting issue is appearantly a non-issue with these. Even in a stone cold manifold!
Oh yeah, no choke (hence the low idle). Oh, and did I forget to mention this engine had some extremely huge streetports? Low end torque may not be that great, but the idle makes me think otherwise. We'll see (it's going into my GLC).If you guys were able to follow along with my post, good for you. I know there's a lot of reading and this subject may only interest the diehards around here. But if you know anything about port size and why Mazda went to tall ports and channeled manifolds for their carbed vehicles some time in the '70s and kept it basically that way through the early '80s, I'd appreciate your input. Which is ultimately better anyway? Is it a potential catch22 like the crappy '81-'85 12A manifolds? Of course newer isn't always better, but what can I combine; new and old, to make it work for me?
Ok back to the baja. I'm leaning toward a Y intermediate to take advantage of the tall ports and less reversion. Should I keep it at 12A port timing? Or go with '74 spec ports? Again, high RPM isn't super important because 4500 is considered high for this thing. Maybe up to 6000 would be fine. The tranny is from a bug with tall gears and the current air cooled VW has a hard time motivating it; you have to wind out 1st gear almost to the 4000 RPM redline just to go into 2nd and have any chance at continuing to accelerate at a decent pace. Hence the need for more low end torque and a high rev limit, but not destructive torque potential like it would be if I went with a V6 or type 4 etc. Let me know what you think.
I'll post pics if it'll make these concepts easier to visualize.
10-29-06, 06:31 PM
#2
on the baja switch to a bus trans i think a 3 rib would be too low of gears but depends on tire size and you will need a stronger trans anyways for the hp. in all reality i would stay with a vw motor and build a type 1 or 4 stroker motor with a countered weighted crank and a good cam will do everything you need and it is easier to find vw parts in the woods or desert than mazda parts. that been my experience when i use to run rails in the woods the guy with the bastard setup if he didn't have spare parts when he broke down to fix it he would be drinking by himself at camp while we would be out having fun and you can't beat the simplicty of a vw (less to break)
10-29-06, 07:05 PM
#3
While I've managed to follow some of this, pics would be a great help. I have seen some of the older parts you mentioned, but not all of them. Side by side pics for comparison will make the visualization easier.
As an additional note, post the hp and torque #s for the different stock setups, along with rpm peaks for each. That may explain some of the variances in port sizes and timings.
When it comes to the port matching and reversion, I can see where having the hard step between the intake and iron would inhibit the reversion. On the flip side of that, if the hard step was smoothed to keep the venturi effect like a carb, the net intake velocity might increase, but it also might increase the reversion.
As far as porting the exhaust, wider yes, up no, down maybe. I wonder if on the baja you couldn't port the exhaust wider than is generally the accepted norm since you will be staying in the low rpms. That may create a greater dynamic effect for the intake by exhausting the burnt mix quicker and starting the intake part of the cycle sooner.
I always enjoy your posts. They either have old school info backed up by real experience, or they are thought provoking teasers like this one. Within the next year I will be building an engine for my REPU from scratch and have not decided what it's getting yet. I'll be watching this to see what kind of results you come up with.
As an additional note, post the hp and torque #s for the different stock setups, along with rpm peaks for each. That may explain some of the variances in port sizes and timings.
When it comes to the port matching and reversion, I can see where having the hard step between the intake and iron would inhibit the reversion. On the flip side of that, if the hard step was smoothed to keep the venturi effect like a carb, the net intake velocity might increase, but it also might increase the reversion.
As far as porting the exhaust, wider yes, up no, down maybe. I wonder if on the baja you couldn't port the exhaust wider than is generally the accepted norm since you will be staying in the low rpms. That may create a greater dynamic effect for the intake by exhausting the burnt mix quicker and starting the intake part of the cycle sooner.
I always enjoy your posts. They either have old school info backed up by real experience, or they are thought provoking teasers like this one. Within the next year I will be building an engine for my REPU from scratch and have not decided what it's getting yet. I'll be watching this to see what kind of results you come up with.
10-30-06, 02:16 AM
#4
Here's the first set of pictures.
The obvious similarities of the J-spec and '74 spec vs the 12A.
And here's where the similarities end.
Just for comparison, the 12A port is between the J-spec and '74 spec in timing.
The camera angle changed between shots, but here you can see the relative port sizes in relation to each other. Interesting, don't you think?
And finally a fairly accurate representation of the differences in exhaust port timing and duration. This shot turned out pretty close to how they look in real life.
By the way, a T2 port opens at the lower line and closes at the upper line, and is 4mm wider (2mm wider on each sidel).
The obvious similarities of the J-spec and '74 spec vs the 12A.
And here's where the similarities end.
Just for comparison, the 12A port is between the J-spec and '74 spec in timing.
The camera angle changed between shots, but here you can see the relative port sizes in relation to each other. Interesting, don't you think?
And finally a fairly accurate representation of the differences in exhaust port timing and duration. This shot turned out pretty close to how they look in real life.
By the way, a T2 port opens at the lower line and closes at the upper line, and is 4mm wider (2mm wider on each sidel).
10-30-06, 02:47 AM
#5
And here's the second set.
The Hitachi carb.
The REPU manifold.
The Jspec manifold with channels and no EGR port (sorta like a '79 manifold).
A different angle. The primary runners are kinda small on this. They're smaller than the REPU manifold. Should be good for low RPM operation.
So what do you think about mixing these short manifold ports with tall Y intermediate ports?
The Hitachi carb.
The REPU manifold.
The Jspec manifold with channels and no EGR port (sorta like a '79 manifold).
A different angle. The primary runners are kinda small on this. They're smaller than the REPU manifold. Should be good for low RPM operation.
So what do you think about mixing these short manifold ports with tall Y intermediate ports?
10-30-06, 03:10 AM
#6
I had forgotten that the short port intermediate from the J-spec engine weighs noticebly more than a Y plate. Heh. From the standpoint of weight reduction, I find I'm leaning further toward the Y plate for the baja.
trochoid, I don't have power figures at my disposal. The US-spec GSL-SE had 135 HP with the best low RPM torque starting at a lower RPM than any other engine (Except maybe the 20B) thanks to its even shorter ports, although it depends whether the engine was US or J-spec. I've seen both examples and one has intermediate and exhaust ports identical in timing to my J-spec. The other has exhaust ports like the REPU and the primary port timing is even smaller. Seriously, the ports are so small it's hard to poke your thumb in it. I'd take pictures but it's currently sitting in my friend's GSL-SE. As for which is J-spec and which is US-spec, I don't know as the engines' pasts are a mystery. I know the RE-EGI came in the Luce as well, so maybe they got one set of ports and the GSL-SE got the other.
I'm sure the carbed 13Bs had less power than 135. Maybe closer to 110 or 105. Heck, even 100HP in a bug would be fast. If I build this thing for a broad torque curve, it will feel more powerful than a peaky streetport. I think the Y plate might help in that regard.
trochoid, I don't have power figures at my disposal. The US-spec GSL-SE had 135 HP with the best low RPM torque starting at a lower RPM than any other engine (Except maybe the 20B) thanks to its even shorter ports, although it depends whether the engine was US or J-spec. I've seen both examples and one has intermediate and exhaust ports identical in timing to my J-spec. The other has exhaust ports like the REPU and the primary port timing is even smaller. Seriously, the ports are so small it's hard to poke your thumb in it. I'd take pictures but it's currently sitting in my friend's GSL-SE. As for which is J-spec and which is US-spec, I don't know as the engines' pasts are a mystery. I know the RE-EGI came in the Luce as well, so maybe they got one set of ports and the GSL-SE got the other.
I'm sure the carbed 13Bs had less power than 135. Maybe closer to 110 or 105. Heck, even 100HP in a bug would be fast. If I build this thing for a broad torque curve, it will feel more powerful than a peaky streetport. I think the Y plate might help in that regard.
10-30-06, 05:30 AM
#7
Jeff, try this link. It appears to have most of the hp/tq #s, no guarentee on accuracy though. http://en.wikipedia.org/wiki/Mazda_Wankel_engine
So the REPU 13B had higher torque #s and larger ports, interesting. That seems to go against the smaller cross-sectional port theory for more intake velocity giving better torque. Maybe because the REPU ports are closer to being a street port than the others that you posted. I'm really quite suprised in the differences in the intake port sizes, particularly on the face of the iron. Another interesting note is is the variances in the exhaust ports. I have a pair of 74-78 13B housings. I'll dig them out and compare them to the 12A, SE and S4 turbo and NA housings I have laying around,
So the REPU 13B had higher torque #s and larger ports, interesting. That seems to go against the smaller cross-sectional port theory for more intake velocity giving better torque. Maybe because the REPU ports are closer to being a street port than the others that you posted. I'm really quite suprised in the differences in the intake port sizes, particularly on the face of the iron. Another interesting note is is the variances in the exhaust ports. I have a pair of 74-78 13B housings. I'll dig them out and compare them to the 12A, SE and S4 turbo and NA housings I have laying around,
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10-30-06, 02:32 PM
#8
The forum just ate my post. 
Let's try this again.
I'm not entirely sure why the REPU engine is the way it is, but I suspect the low diff gearing allows the engine to climb up to its powerband sooner. Also since rotaries tend to shift their torque higher in the RPM band when you port them, the diff gearing choice makes sense. It's also better for towing.
The exhaust ports are still only as large as any other US-spec 13B from the '70s, but with one major difference: the sleeves are smaller. I suspect this keeps exhaust gas velocity higher for more power. Obviously more noise as well.
Note to those who don't know what I'm talkin about, the the exhaust sleeves of all '76 and later engines acted like a kind of mini expansion chamber slowing the exhaust gasses down right after they exit the port. It flows from a small area to a large area rather quickly before it enters the header/manifold/turbo etc. This drops the velocity down dramatically and also effectively quiets them to some degree. The '74 spec rotor housings have a much smaller sleeve, and all the benefits and problems they produce.
So whether REPU ports really do go against the cross-sectional port theory or not is probably moot due to the exhaust port timing, sleeve size and diff gearing all working together. We could probably debate this forever but I'd rather go with what I think will work best. If that means 'upgrading' some parts so that the engine is no longer an entirely true '74 spec engine, so be it.
Racing Beat's template extends to 60° intake closing, with earlier opening. '74 spec closes at 50° if I'm not mistaken, with normal opening. Stock US spec '76-'85 12A and the carbed 13Bs is 40°. The tiny J-spec port pictured above is probably 30°.
By the way, my other REPU has a streetported 4 port 13B with rejetted Hitachi carb and it performs somewhat sluggishly at lower RPM. Also since the carb has vacuum secondaries, they don't kick in very hard when it's just me driving it; it needs more of a load like cargo, a weighty passenger, and a medium uphill grade to open them reliably. Then the real power of that engine can be utilized. In other words, it's not very practical. The truck used to have an entirely stock ported nitrided R5 13B, complete with tall intermediate ports, 40° intake port timing and US-spec 13B exhaust port timing. This truck used to fly on a dellorto or stock jetted Hitachi. Then the previous owner thought it would be good to streetport it during a rebuild. After that, the dellorto only had decent power between 2k and 4k. The Hitachi is the only carb that works half decently now as I don't have a Holley or whatever. Again the only time this engine has decent power now is when the secondaries open, and they only do that reliably when there is a heavy load. Level street? Accelerating from a stoplight? Good luck.
The streetport size I used is between 55 and 60 degrees with earlier opening as well. Not as extreme as Racing Beat. I call it a mild streetport. The exhaust ports are a crappy upside down D shape. They open at US spec and are curved (rounded) up to T2 spec, or maybe a little higher (not more than 5° I think). They're narrow, too. I'll correct it eventually. Probably to T2 spec or close to it as seen here. Maybe do a supercharger too.
See those two sets of marker lines? The lower line represents a stock T2 port. The upper line is where I ported to. I also opened the port a tad sooner than stock with the addition of a slight rounded edge for a correct D shape. Wider to T2 width as well.
That rotor housing on the left went into a nitrided R5 13B with 60° closing secondaries and 55° closing primaries and was temporarily test run in my REPU. It had my '74 carb pictured here.
That's the engine that idled to 600RPM within 2 minutes of first-start run time with no choke on a channeled manifold. The exhaust consisted of an R5 13B manifold (resembles an '81-'83 12A exhaust manifold with no O2 sensor, obviously) and a 1.5' downpipe into a half dead Rotary Engineering glasspack. I didn't need hearing protection, but it was painfully loud when I'd stab the throttle (no fuel-wetting issues). To see this engine in an earlier form, check this thread. https://www.rx7club.com/forum/showth...&highlight=13B
It can be quite educational to set all these parts side by side and compare them keeping in mind their original purpose. The more parts the better. You only really need one example. I only have one S4 T2 rotor housing that I've copied to make T2 sized exhaust ports in '85 and older rotor housings. You can see how it compares to this rotor housing after correcting the upside down D mistake.
The 3B intermediate plate has been worth its weight in gold for the number of times I've copied its port. It's good when your porting choices aren't limited to either stock or Racing Beat's template.
Let's get back to the original question. Since both of my engines came stock with short port intermediate plates, pictured above, and since I have access to a couple tallport Y intermediate plates, and we have a basic understanding for why Mazda went with tall ports and channels in the manifolds, and I've had excellent results cutting my own channels and using a '74 carb on an engine with some huge ports, should I take advantage of these later upgrades, regardless of whether they were intended for better gas mileage or whatever, and replace both short port plates with tall port plates, channeled manifolds, and both Hitachi carbs pictured above?
Here's a pretty good argument in favor of tall port intermediate plates. Last year I rebuilt an R5 13B for a friend with an automatic REPU. I ported the primary and secondary ports to '74 spec and only cleaned the exhaust ports - their timing remained stock. I didn't touch the intake manifold. The only things this engine needed were soft seals and springs. All the hard seals and even apex seals were fine. I'd never seen such little wear on an R5 engine before. It can be seen sitting next to my R5 here (it's the one on the right).
After his engine was broken in, he gave me a ride. I couldn't believe how much power it had. Especially for an automatic. My automatic Cosmo isn't fast like that. It had a totally stock '74 carb (which I rebuilt reusing all of the old parts; they were in such good shape) and a totally stock intake manifold (before I knew about cutting channels). You can see a stock '74 manifold pictured here.
The exhaust has an RB header, and a couple mufflers. Perhaps even a stock REPU muffler (I didn't study the exhaust). It's not quiet but not loud and sounds pretty healthy when he revs it.
His truck is absolutely phenominal. I want performance like that. Makes me wish I didn't streetport the R5 in my other REPU. Well, I have enough parts to reproduce his engine for at least one of my REPUs. Instead of R5 plates it'll use its original 3B plates front and rear, and a Y intermediate. It could cause problems with the number of tension bolt holes being 19 on the rear plate but only 18 holes in the intermediate. I ran into a similar problem in my bro's RX-4 which had 19 holes, but the GSL-SE rotor housings employ oil injectors which block one of the bolts. I cut NPT threads in the rear plate and installed a brass plug fitting. No leaks.
Well there you go. I think I've made my decision. I think I'll use Y intermediate plates in these engines and ditch the short ports. Thoughts?
Oh, I just though of another pro-tall port example. My Cosmo has tall ports and was supposed to use a reversed runner manifold. Well that manifold has to go into my MG because it fits beautifully, and the Cosmo has a rock solid idle on an unchannled '74 manifold and a mostly stock jetted '77 carb. Of course the carb was designed to work on a seperate runner manifold as far as I know, being a '77 model, (I'm not sure when Mazda transisitioned, but '78 was definitely channeled), but so was the '74 carb, and it performed exceptionally well on a channeled manifold. Go figure. Anyway the idle is strong and smooth. I suspect the low RPM torque would be greater if it had its original reversed runner manifold, but if I eventually go with a supercharger like my bro's RX-4, and swap in a stickshift, it's not really going to matter anymore.
My friend's REPU's idle, however, is not very smooth. Both vehicles are automatics, and they're both driveable and all that, but his has audible misses now and then. Both have the DLIDFIS upgrade as well. His has a header and the Cosmo has a thermal reactor. Now if you recall what I said earlier about my freshly rebuilt large streetported R5 that ran smooth as silk in my REPU with a channeled manifold and not much of an exhaust? I've noticed that headers tend to make a smooth idle lumpy. What they take away from the idle, they give back with interest above idle. The point is that his idle is lumpy either because of the header, or the seperate runner manifold. Or maybe both. My Cosmo and big streetport are smooth either because there is no header, or maybe some other factor. Further complicating the issue is back when my REPU's engine was in my MG, it idled smooth with a short header and the Cosmo's reversed runner manifold flowing into the secondary ports, which were obviously at '74 spec, and the intermediate ports were no bigger than the J-spec pictured above. It's an NO casting. Short ports all the way through, yet the manifold had tall ports because they were secondaries. I think I forgot to mention that that's the whole reason why I got into all this port stuff in the first place; it was to correct my REPU engine and build something nice for the MG, then the REPU and finally the baja. Come to find out I may not even use the 3B intermediate in the REPU engine after all... I wouldn't blame you if you're confused at this point.
Yeah, I forgot to mention the MG. I've gotta build three 4 port 13Bs over the fall. One for the MG, one for the REPU, and one for the baja. I've got two sets of '74 REPU rotor housings; two ported with the awefull upside down D shape which will be corrected, two stock US-spec, and one set of J-spec housings with later closing and later opening.
Two complete sets of Y plates; front middle and rear, and one extra Y intermediate which I think will go into the REPU engine ported to '74 spec. The set for the MG is already ported to '74 spec because this little car performed so well with the REPU's engine in it. (not to mention all the other engines with '74 spec which have performed better than expected too, hehe)
One complete set of 3B plates. One heavy duty REPU flywheel and clutch assembly. Two auto rear counerweights. One RB light steel flywheel. One decent 215mm disc and pressure plate. Three Hitachi carbs: J-spec, '74 and '77. Three manifolds; Cosmo reversed runner for MG, '74 to receive channels for REPU, and J-spec for baja. I already cut channels in the Cosmo manifold seen here.
They're not as deep as in the other manifold because there is less material, but I bet they'll work just fine. Here's a shot of the REPU engine after I pulled it from the MG. A nice view of the Cosmo manifold.
Let's try this again.I'm not entirely sure why the REPU engine is the way it is, but I suspect the low diff gearing allows the engine to climb up to its powerband sooner. Also since rotaries tend to shift their torque higher in the RPM band when you port them, the diff gearing choice makes sense. It's also better for towing.
The exhaust ports are still only as large as any other US-spec 13B from the '70s, but with one major difference: the sleeves are smaller. I suspect this keeps exhaust gas velocity higher for more power. Obviously more noise as well.
Note to those who don't know what I'm talkin about, the the exhaust sleeves of all '76 and later engines acted like a kind of mini expansion chamber slowing the exhaust gasses down right after they exit the port. It flows from a small area to a large area rather quickly before it enters the header/manifold/turbo etc. This drops the velocity down dramatically and also effectively quiets them to some degree. The '74 spec rotor housings have a much smaller sleeve, and all the benefits and problems they produce.
So whether REPU ports really do go against the cross-sectional port theory or not is probably moot due to the exhaust port timing, sleeve size and diff gearing all working together. We could probably debate this forever but I'd rather go with what I think will work best. If that means 'upgrading' some parts so that the engine is no longer an entirely true '74 spec engine, so be it.
Racing Beat's template extends to 60° intake closing, with earlier opening. '74 spec closes at 50° if I'm not mistaken, with normal opening. Stock US spec '76-'85 12A and the carbed 13Bs is 40°. The tiny J-spec port pictured above is probably 30°.
By the way, my other REPU has a streetported 4 port 13B with rejetted Hitachi carb and it performs somewhat sluggishly at lower RPM. Also since the carb has vacuum secondaries, they don't kick in very hard when it's just me driving it; it needs more of a load like cargo, a weighty passenger, and a medium uphill grade to open them reliably. Then the real power of that engine can be utilized. In other words, it's not very practical. The truck used to have an entirely stock ported nitrided R5 13B, complete with tall intermediate ports, 40° intake port timing and US-spec 13B exhaust port timing. This truck used to fly on a dellorto or stock jetted Hitachi. Then the previous owner thought it would be good to streetport it during a rebuild. After that, the dellorto only had decent power between 2k and 4k. The Hitachi is the only carb that works half decently now as I don't have a Holley or whatever. Again the only time this engine has decent power now is when the secondaries open, and they only do that reliably when there is a heavy load. Level street? Accelerating from a stoplight? Good luck.
The streetport size I used is between 55 and 60 degrees with earlier opening as well. Not as extreme as Racing Beat. I call it a mild streetport. The exhaust ports are a crappy upside down D shape. They open at US spec and are curved (rounded) up to T2 spec, or maybe a little higher (not more than 5° I think). They're narrow, too. I'll correct it eventually. Probably to T2 spec or close to it as seen here. Maybe do a supercharger too.
See those two sets of marker lines? The lower line represents a stock T2 port. The upper line is where I ported to. I also opened the port a tad sooner than stock with the addition of a slight rounded edge for a correct D shape. Wider to T2 width as well.
That rotor housing on the left went into a nitrided R5 13B with 60° closing secondaries and 55° closing primaries and was temporarily test run in my REPU. It had my '74 carb pictured here.
It can be quite educational to set all these parts side by side and compare them keeping in mind their original purpose. The more parts the better. You only really need one example. I only have one S4 T2 rotor housing that I've copied to make T2 sized exhaust ports in '85 and older rotor housings. You can see how it compares to this rotor housing after correcting the upside down D mistake.
The 3B intermediate plate has been worth its weight in gold for the number of times I've copied its port. It's good when your porting choices aren't limited to either stock or Racing Beat's template.
Let's get back to the original question. Since both of my engines came stock with short port intermediate plates, pictured above, and since I have access to a couple tallport Y intermediate plates, and we have a basic understanding for why Mazda went with tall ports and channels in the manifolds, and I've had excellent results cutting my own channels and using a '74 carb on an engine with some huge ports, should I take advantage of these later upgrades, regardless of whether they were intended for better gas mileage or whatever, and replace both short port plates with tall port plates, channeled manifolds, and both Hitachi carbs pictured above?
Here's a pretty good argument in favor of tall port intermediate plates. Last year I rebuilt an R5 13B for a friend with an automatic REPU. I ported the primary and secondary ports to '74 spec and only cleaned the exhaust ports - their timing remained stock. I didn't touch the intake manifold. The only things this engine needed were soft seals and springs. All the hard seals and even apex seals were fine. I'd never seen such little wear on an R5 engine before. It can be seen sitting next to my R5 here (it's the one on the right).
After his engine was broken in, he gave me a ride. I couldn't believe how much power it had. Especially for an automatic. My automatic Cosmo isn't fast like that. It had a totally stock '74 carb (which I rebuilt reusing all of the old parts; they were in such good shape) and a totally stock intake manifold (before I knew about cutting channels). You can see a stock '74 manifold pictured here.
The exhaust has an RB header, and a couple mufflers. Perhaps even a stock REPU muffler (I didn't study the exhaust). It's not quiet but not loud and sounds pretty healthy when he revs it.
His truck is absolutely phenominal. I want performance like that. Makes me wish I didn't streetport the R5 in my other REPU. Well, I have enough parts to reproduce his engine for at least one of my REPUs. Instead of R5 plates it'll use its original 3B plates front and rear, and a Y intermediate. It could cause problems with the number of tension bolt holes being 19 on the rear plate but only 18 holes in the intermediate. I ran into a similar problem in my bro's RX-4 which had 19 holes, but the GSL-SE rotor housings employ oil injectors which block one of the bolts. I cut NPT threads in the rear plate and installed a brass plug fitting. No leaks.
Well there you go. I think I've made my decision. I think I'll use Y intermediate plates in these engines and ditch the short ports. Thoughts?
Oh, I just though of another pro-tall port example. My Cosmo has tall ports and was supposed to use a reversed runner manifold. Well that manifold has to go into my MG because it fits beautifully, and the Cosmo has a rock solid idle on an unchannled '74 manifold and a mostly stock jetted '77 carb. Of course the carb was designed to work on a seperate runner manifold as far as I know, being a '77 model, (I'm not sure when Mazda transisitioned, but '78 was definitely channeled), but so was the '74 carb, and it performed exceptionally well on a channeled manifold. Go figure. Anyway the idle is strong and smooth. I suspect the low RPM torque would be greater if it had its original reversed runner manifold, but if I eventually go with a supercharger like my bro's RX-4, and swap in a stickshift, it's not really going to matter anymore.
My friend's REPU's idle, however, is not very smooth. Both vehicles are automatics, and they're both driveable and all that, but his has audible misses now and then. Both have the DLIDFIS upgrade as well. His has a header and the Cosmo has a thermal reactor. Now if you recall what I said earlier about my freshly rebuilt large streetported R5 that ran smooth as silk in my REPU with a channeled manifold and not much of an exhaust? I've noticed that headers tend to make a smooth idle lumpy. What they take away from the idle, they give back with interest above idle.
The point is that his idle is lumpy either because of the header, or the seperate runner manifold. Or maybe both. My Cosmo and big streetport are smooth either because there is no header, or maybe some other factor. Further complicating the issue is back when my REPU's engine was in my MG, it idled smooth with a short header and the Cosmo's reversed runner manifold flowing into the secondary ports, which were obviously at '74 spec, and the intermediate ports were no bigger than the J-spec pictured above. It's an NO casting. Short ports all the way through, yet the manifold had tall ports because they were secondaries. I think I forgot to mention that that's the whole reason why I got into all this port stuff in the first place; it was to correct my REPU engine and build something nice for the MG, then the REPU and finally the baja. Come to find out I may not even use the 3B intermediate in the REPU engine after all... I wouldn't blame you if you're confused at this point.Yeah, I forgot to mention the MG. I've gotta build three 4 port 13Bs over the fall. One for the MG, one for the REPU, and one for the baja. I've got two sets of '74 REPU rotor housings; two ported with the awefull upside down D shape which will be corrected, two stock US-spec, and one set of J-spec housings with later closing and later opening.
Two complete sets of Y plates; front middle and rear, and one extra Y intermediate which I think will go into the REPU engine ported to '74 spec. The set for the MG is already ported to '74 spec because this little car performed so well with the REPU's engine in it.
(not to mention all the other engines with '74 spec which have performed better than expected too, hehe)One complete set of 3B plates. One heavy duty REPU flywheel and clutch assembly. Two auto rear counerweights. One RB light steel flywheel. One decent 215mm disc and pressure plate. Three Hitachi carbs: J-spec, '74 and '77. Three manifolds; Cosmo reversed runner for MG, '74 to receive channels for REPU, and J-spec for baja. I already cut channels in the Cosmo manifold seen here.
They're not as deep as in the other manifold because there is less material, but I bet they'll work just fine. Here's a shot of the REPU engine after I pulled it from the MG. A nice view of the Cosmo manifold.
10-30-06, 03:36 PM
#9
Originally Posted by Jeff20B
... I wouldn't blame you if you're confused at this point.
Well I'm glad you seem to be making some progress by just typing this out. Seams like your coming up with the answer though your own reasoning.
But I must say it was interesting to read. And I'm now going to sit in the corner of the class with the dunce (sp) cap on and hope I learn something because I obviously have a lot to learn.
10-31-06, 12:55 AM
#12
What parts do you want pics of? I have 12A, S4 TII, S4 NA and 74-78 13B housings. I haven't torn down the lone SE engine yet. Also have irons for all of the housings except the early 13B. Most of my parts are S3/4. I haven't been 'collecting' as long as you have. lol
I also have an old Jay-Tech Holley style intake mani that I can't figure out what it fits, unless it's for an REW.
I also have an old Jay-Tech Holley style intake mani that I can't figure out what it fits, unless it's for an REW.
10-31-06, 10:34 AM
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Originally Posted by Directfreak
Want torque in an N/A? Build a 6 port. With working actuators.
10-31-06, 10:39 AM
#17
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jeff- i dont know if you saw it but i posted a similar thread on nopistons, but i was looking at the 86+ stuff, its like these engines, it doesnt make sense....
the cosmo 13b's have teeny little primary ports (like your j spec), but huge runners,
while the fd engines have a smaller runner, and larger primaries.
the fd and cosmo have the same sized runners, but the cosmo's got larger secondary ports
the cosmo engine is designed to live in a heavy car with an automatic, why does it have larger runners? but small ports? shouldnt it have small runners and ports?
the cosmo 13b's have teeny little primary ports (like your j spec), but huge runners,
while the fd engines have a smaller runner, and larger primaries.
the fd and cosmo have the same sized runners, but the cosmo's got larger secondary ports
the cosmo engine is designed to live in a heavy car with an automatic, why does it have larger runners? but small ports? shouldnt it have small runners and ports?
10-31-06, 02:49 PM
#18
FirebirdSlayer666, maybe. Keep reading. Actually, I already did in my bro's RX-4. Check the other rotaries section.
trochoid, any parts you think would be appropriate. Actually, I do have a request. If you could show us your '70s 13B rotor housings, and point out any differences in sleeve size, port timing/duration etc, that would be great.
MtotheIKEo, neither of them do. They originally had points ignition. Mazda added the raised sections (three bits or a semi-circle) to prevent people from installing points style or any other non-rotary plugs. The BR8EQ-14 and later plugs all had longer middle sections to extend the 6 point hex outward for easy installation with a regular spark plug socket. You can either trim the aluminum or get a thinwall socket from Racing Beat. I personally don't bother with either as I use electronic ignition and the later plugs in all my engines.
The rotor housing on the left is J-spec from the '70s. It's missing some chrome so I won't use it in the baja engine.
Directfreak, I would if I could. Actually, maybe not. Keep reading.
Mike, that's a good point. Of course being fuel injected with a progressive TB probably has something to do with it. The steep manifold angle may also have something to do with it. But since the TB is progressive and the primary ports don't have much duration, it must be mainly for really low RPM off boost parking lot stuff. Of course during any kind of acceleration, the primaries are only open by themselves for a short period of time anyway. Don't the secondary butterflies begin to open at 10% throttle opening? I know about the choke butterflies, but I don't know when they open.
The Hitachi is not progressive, therefore the primary ports must take it all until the secondary barrels open. That is probably why they have more port timing/port duration (well, most 12As and some 13Bs). As for the tall intermediate runners, it's gotta be to reduce reversion. Gotta be. That J-spec is just weird.
I'm almost at the point where I just want to go for it and try the tall port Y plates in both engines. I've gathered enough subjective evidence to show that Mazda's late addition of tall primary ports and channels in the manifolds to their carbed engine lineup was to reduce reversion and emissions while increasing power and driveability. Something Mazda probably should have done from the beginning, like direct fire, but we can upgrade their early engines with these later parts and benefit just the same.
Since I've tested the J-spec carb with great success, after swapping air bleeds and jets, on my stock ported (tall ported) Cosmo with an unchanneled manifold, as well as my bro's streetported (tall ported) RX-4 with a channeled manifold, and since one is an auto, the other a stick, this carb is certainly viable for whatever I plan to do. Some engine puller/importer cut all the wires and damaged the choke vacuum thing so the choke is essentially useless unless I can source some Hitachi parts. I'm not inclined to run a choke cable from front to back in the baja, so this is just another pro-baja 'feature' I suppose.
I haven't actually ran its manifold (the J-spec pictured above) on anything yet, but the RX-4's manifold is almost identical with the only difference being the runner diameter, and the carb worked fine on it. The J-spec is narrower by a couple mm. The RX-4 is sorta medium in diameter. The '74 manifold has runners the same size as the carb barrels. The J-spec manifold will flow perhaps better at low RPM than the '74 manifolds, and maybe not as well at higher RPM. Another pro-baja feature? You better believe it! Will it act like a bottleneck though?
If I had access to a complete 6 port, all the manifolding, an ECU and was inclined to do all the wiring so it couldn't fall off with the type of driving I'm planning to do, I'd still hesitate. Total power and torque would be greater, but the extra dimension of complication is a real turnoff. I guess I'm not like you EFI guys. A 20B with a megasquirt is all I can handle. More than, actually. I don't enjoy working on it as much as a simple carb setup. Rotaries are supposed to be simple, and this baja will reflect that.
I guess now I understand why some ACVW guys are purists; to keep pouring money into a gutless, finiky, not very reliable and yes complicated engine is something I would never do, but I can respect others for having the grapes to baja one of these things and the other cool stuff they do with them. I'm affraid I'd hurt it or overrev it or something, and I don't care to learn all the quirks of these things; what to do, what not to do etc. I can't afford to hotrod an ACVW, but a simple, reliable, carbed, unported 13B with new seals and adequate cooling will cost much less now and in the long run, have respectable power and driveability, and if it does break down, I've already got the infrastructure to rebuild it. Not so with VW parts. My local bug shop guy relocated to Tacoma recently so I can't limp it over his shop now.
Time to upgrade to rotary power? Yes. Gonna use tall port Y intermediate plates? Yes. gonna port them? Hmm... My Cosmo isn't ported and the low end torque is nice, for what it is. My friend's REPU has '74 spec ports, but I suspect the automatic is screwing with my sense of seat of the pants feedback. My MG with the REPU's engine was awesome. However the gearing, reversed runner manifold, featherweight lightness, and the light steel flywheel were probably also coloring the feedback. Don't get me wrong it was scary fast like nobody's business but I rarely got into the secondaries because A they sucked (tall flowing into short NO ports), and B the brakes were almost nill. Last but not least is PercentsevenC's GSL. It also got '74 ports and when it had a modded Nikki and a nice manifold right after the rebuild, it was breaking in and we couldn't test for power gains. Then we had to reinstall the stock rat's nest and crappy FB manifold and carb. It's gutless on primaries now but the secondaries can open at medium RPM and add noticeable power. I'll probably trade one of my finished car projects to him for his GSL in January, and you know the cool carb and manifold will go back on. Then I can finally experience true to form '74 ports in a 1st gen. Well that's great but what does it have to do with the subject at hand?
Even with all my rotary experience (real or imagined lol), I've never actually attempted an engine like this before, so I don't know whether I should port it and risk ruining any potential low end torque it might have, or leave it alone. I think I've at least settled the tall port vs short port debate for reasons of weight reduction, reversion, carb is compatible etc, but that is all one sided because I've never actually driven an engine with short ports that worked well. My REPU's engine had a stupid NO plate which physically looks similar to the J-spec. Same size ports etc. It was pretty crappy, and the engine came to life after I installed the reversed runner manifold. The secondaries sucked, but since I did 90% of my driving on primaries, it was a good compromise until I could rebuild it with the proper parts. Now that I have the correct intermediate plate, I don't think I want to use it.
Maybe I shouldn't port the baja engine. I can always port it later; the only cost being a gasket set and some time. How about this: using the REPU as an example, I won't port the baja engine while it's got the relatively weak taller geared bug tranny. Then when I can upgrade to a 3 or 5 rib bus tranny, I'll port the engine to '74 spec to take advantage of the bus tranny's shorter final drive and the rotary's decreased torque at lower RPM, and the bus tranny's extra strength should handle the increased torque at higher RPM. I could even boost it at that point if I was so inclined.
What do you guys think about that idea?
Actually, I already did in my bro's RX-4. Check the other rotaries section.trochoid, any parts you think would be appropriate. Actually, I do have a request. If you could show us your '70s 13B rotor housings, and point out any differences in sleeve size, port timing/duration etc, that would be great.
MtotheIKEo, neither of them do. They originally had points ignition. Mazda added the raised sections (three bits or a semi-circle) to prevent people from installing points style or any other non-rotary plugs. The BR8EQ-14 and later plugs all had longer middle sections to extend the 6 point hex outward for easy installation with a regular spark plug socket. You can either trim the aluminum or get a thinwall socket from Racing Beat. I personally don't bother with either as I use electronic ignition and the later plugs in all my engines.
The rotor housing on the left is J-spec from the '70s. It's missing some chrome so I won't use it in the baja engine.
Directfreak, I would if I could. Actually, maybe not. Keep reading.
Mike, that's a good point. Of course being fuel injected with a progressive TB probably has something to do with it. The steep manifold angle may also have something to do with it. But since the TB is progressive and the primary ports don't have much duration, it must be mainly for really low RPM off boost parking lot stuff. Of course during any kind of acceleration, the primaries are only open by themselves for a short period of time anyway. Don't the secondary butterflies begin to open at 10% throttle opening? I know about the choke butterflies, but I don't know when they open.
The Hitachi is not progressive, therefore the primary ports must take it all until the secondary barrels open. That is probably why they have more port timing/port duration (well, most 12As and some 13Bs). As for the tall intermediate runners, it's gotta be to reduce reversion. Gotta be. That J-spec is just weird.
I'm almost at the point where I just want to go for it and try the tall port Y plates in both engines. I've gathered enough subjective evidence to show that Mazda's late addition of tall primary ports and channels in the manifolds to their carbed engine lineup was to reduce reversion and emissions while increasing power and driveability. Something Mazda probably should have done from the beginning, like direct fire, but we can upgrade their early engines with these later parts and benefit just the same.
Since I've tested the J-spec carb with great success, after swapping air bleeds and jets, on my stock ported (tall ported) Cosmo with an unchanneled manifold, as well as my bro's streetported (tall ported) RX-4 with a channeled manifold, and since one is an auto, the other a stick, this carb is certainly viable for whatever I plan to do. Some engine puller/importer cut all the wires and damaged the choke vacuum thing so the choke is essentially useless unless I can source some Hitachi parts. I'm not inclined to run a choke cable from front to back in the baja, so this is just another pro-baja 'feature' I suppose.
I haven't actually ran its manifold (the J-spec pictured above) on anything yet, but the RX-4's manifold is almost identical with the only difference being the runner diameter, and the carb worked fine on it. The J-spec is narrower by a couple mm. The RX-4 is sorta medium in diameter. The '74 manifold has runners the same size as the carb barrels. The J-spec manifold will flow perhaps better at low RPM than the '74 manifolds, and maybe not as well at higher RPM. Another pro-baja feature? You better believe it! Will it act like a bottleneck though?
If I had access to a complete 6 port, all the manifolding, an ECU and was inclined to do all the wiring so it couldn't fall off with the type of driving I'm planning to do, I'd still hesitate. Total power and torque would be greater, but the extra dimension of complication is a real turnoff. I guess I'm not like you EFI guys. A 20B with a megasquirt is all I can handle. More than, actually. I don't enjoy working on it as much as a simple carb setup. Rotaries are supposed to be simple, and this baja will reflect that.
I guess now I understand why some ACVW guys are purists; to keep pouring money into a gutless, finiky, not very reliable and yes complicated engine is something I would never do, but I can respect others for having the grapes to baja one of these things and the other cool stuff they do with them. I'm affraid I'd hurt it or overrev it or something, and I don't care to learn all the quirks of these things; what to do, what not to do etc. I can't afford to hotrod an ACVW, but a simple, reliable, carbed, unported 13B with new seals and adequate cooling will cost much less now and in the long run, have respectable power and driveability, and if it does break down, I've already got the infrastructure to rebuild it. Not so with VW parts. My local bug shop guy relocated to Tacoma recently so I can't limp it over his shop now.
Time to upgrade to rotary power? Yes. Gonna use tall port Y intermediate plates? Yes. gonna port them? Hmm... My Cosmo isn't ported and the low end torque is nice, for what it is. My friend's REPU has '74 spec ports, but I suspect the automatic is screwing with my sense of seat of the pants feedback. My MG with the REPU's engine was awesome. However the gearing, reversed runner manifold, featherweight lightness, and the light steel flywheel were probably also coloring the feedback. Don't get me wrong it was scary fast like nobody's business but I rarely got into the secondaries because A they sucked (tall flowing into short NO ports), and B the brakes were almost nill. Last but not least is PercentsevenC's GSL. It also got '74 ports and when it had a modded Nikki and a nice manifold right after the rebuild, it was breaking in and we couldn't test for power gains. Then we had to reinstall the stock rat's nest and crappy FB manifold and carb. It's gutless on primaries now but the secondaries can open at medium RPM and add noticeable power. I'll probably trade one of my finished car projects to him for his GSL in January, and you know the cool carb and manifold will go back on. Then I can finally experience true to form '74 ports in a 1st gen. Well that's great but what does it have to do with the subject at hand?
Even with all my rotary experience (real or imagined lol), I've never actually attempted an engine like this before, so I don't know whether I should port it and risk ruining any potential low end torque it might have, or leave it alone. I think I've at least settled the tall port vs short port debate for reasons of weight reduction, reversion, carb is compatible etc, but that is all one sided because I've never actually driven an engine with short ports that worked well. My REPU's engine had a stupid NO plate which physically looks similar to the J-spec. Same size ports etc. It was pretty crappy, and the engine came to life after I installed the reversed runner manifold. The secondaries sucked, but since I did 90% of my driving on primaries, it was a good compromise until I could rebuild it with the proper parts. Now that I have the correct intermediate plate, I don't think I want to use it.
Maybe I shouldn't port the baja engine. I can always port it later; the only cost being a gasket set and some time. How about this: using the REPU as an example, I won't port the baja engine while it's got the relatively weak taller geared bug tranny. Then when I can upgrade to a 3 or 5 rib bus tranny, I'll port the engine to '74 spec to take advantage of the bus tranny's shorter final drive and the rotary's decreased torque at lower RPM, and the bus tranny's extra strength should handle the increased torque at higher RPM. I could even boost it at that point if I was so inclined.
What do you guys think about that idea?
10-31-06, 04:28 PM
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Originally Posted by Jeff20B
MtotheIKEo, neither of them do. They originally had points ignition. Mazda added the raised sections (three bits or a semi-circle) to prevent people from installing points style or any other non-rotary plugs. The BR8EQ-14 and later plugs all had longer middle sections to extend the 6 point hex outward for easy installation with a regular spark plug socket. You can either trim the aluminum or get a thinwall socket from Racing Beat. I personally don't bother with either as I use electronic ignition and the later plugs in all my engines.
10-31-06, 06:43 PM
#21
Hey those rotor housings look familiar.
Chances are they're J-spec like that one you asked about in the picture. Your engine could either be a stock never opened, or maybe it was rebuilt at some point.
Can you tell me what the top of the intermediate plate looks like? Your three choices are:
1) machined flat with two threaded holes
2) not machined with casting flash visible
3) a cover plate over an EGR port, or just any cover plate
A yes on one of those three will narrow down the possibilities significantly.
Also, if you could tell me about the heater core fitting in the lower right of the picture, maybe I could narrow it down for you some more. Does it have a 6 point hex? Or is the rubber hose butted all the way against the plate?
Is there an oil pressure sender hole under the oil filter pedestal in the usual place? Perhaps with a little allen head plug? Or just a blank casting? Note it is just to the right of the temp sender out of view in your picture.
Look around the intermediate plate for R, R5 or NO up near the PCV breather tubes.
Edit: if the intermediate is a Y, look on the front side down near the spark plugs. I think it will be partially obscured by the rotor housing if I remember right.
Chances are they're J-spec like that one you asked about in the picture. Your engine could either be a stock never opened, or maybe it was rebuilt at some point.
Can you tell me what the top of the intermediate plate looks like? Your three choices are:
1) machined flat with two threaded holes
2) not machined with casting flash visible
3) a cover plate over an EGR port, or just any cover plate
A yes on one of those three will narrow down the possibilities significantly.
Also, if you could tell me about the heater core fitting in the lower right of the picture, maybe I could narrow it down for you some more. Does it have a 6 point hex? Or is the rubber hose butted all the way against the plate?
Is there an oil pressure sender hole under the oil filter pedestal in the usual place? Perhaps with a little allen head plug? Or just a blank casting? Note it is just to the right of the temp sender out of view in your picture.
Look around the intermediate plate for R, R5 or NO up near the PCV breather tubes.
Edit: if the intermediate is a Y, look on the front side down near the spark plugs. I think it will be partially obscured by the rotor housing if I remember right.
Last edited by Jeff20B; 10-31-06 at 06:47 PM.
10-31-06, 07:23 PM
#22
Jeff, I'll get pics posted up in a couple of days. It's time I tore down the SE engine and I will add those housings to the pics.
With all of the different versions/editions of parts you have, along with the extensive knowledge you have about them, you should do a seperate thread for each of the following: Carbs, intakes, housings, irons, rotors and counterweights f/r. They would make a great reference data base for the archives. I'm sure that any parts or pics of them that you don't have on hand will happily be provided by other members.
As far as building the engine for your REPU and shooting for the most low end torque, if you can mount a carb that keeps the primary air flow seperate from the secondary, but has the bridge groove between the front and rear rotors in the primarys for the dynamic effect, I would be inclined to clean up the primarys and not port them at all. Then port the secondarys for higher air flow in the upper rpm range. This is in a sense what the 6-port engines do, but I don't recall whether the 74-78 4-ports or the 6-port SEs produce more more low end torque nor over what rpm range.
Thanks for inviting me to the party, it's looking like it will be a fun and very educational one.
With all of the different versions/editions of parts you have, along with the extensive knowledge you have about them, you should do a seperate thread for each of the following: Carbs, intakes, housings, irons, rotors and counterweights f/r. They would make a great reference data base for the archives. I'm sure that any parts or pics of them that you don't have on hand will happily be provided by other members.
As far as building the engine for your REPU and shooting for the most low end torque, if you can mount a carb that keeps the primary air flow seperate from the secondary, but has the bridge groove between the front and rear rotors in the primarys for the dynamic effect, I would be inclined to clean up the primarys and not port them at all. Then port the secondarys for higher air flow in the upper rpm range. This is in a sense what the 6-port engines do, but I don't recall whether the 74-78 4-ports or the 6-port SEs produce more more low end torque nor over what rpm range.
Thanks for inviting me to the party, it's looking like it will be a fun and very educational one.
10-31-06, 09:28 PM
#23
I look forward to pics of your GSL-SE ports. Is it a US-spec engine? I didn't get any pictures of the GSL-SE housings we used in my bro's RX-4 before or after we ported them. The ports began life with the exact same timing as the J-spec rotor housing above, then progressed to T2 spec. The lost-seal GSL-SE core I tore down a few months ago had rotor housings with ports that matched the smaller, sooner opening and closing port on the right. I could get pictures of them and the end plates pretty soon. Only the intermediate plate is indisposed at the moment; it's sitting in a mockup in my friend's GSL-SE. After I build a header, the engine can come out and get torn back down. Then if I still remember this thread, I'll take a few comparison pictures.
The idea to make several threads with specifc themes sounds good, if I can be arsed to do it.
I can only post substantively about what I know about the parts I have, of course. There will be very little 2nd gen content. lol
Oh, I do have one picture of the GSL-SE core before it was torn down.
Looks like any other GSL-SE engine from the outside. Probably the only way to tell which set of ports it had is to look into the rotor housings. Not a very easy task most of the time, as you can imagine.
What do you mean by the bridge groove thing? The J-spec carb spacer had a bridge cut between both primaries, and must have worked alongside the channels in the manifold some how. The carb spacer is currently on my Cosmo and the idle and low end are decent. Should I steal it for the baja?
Does anybody have old reference dyno charts of HP and torque curves for stock REPUs, RX-4s, Cosmos etc? Oh, and an RX-3 SP thrown in for good measure? Even though it's a 12A, the SP should have a channeled manifold or a reversed runner manifold, being availiable in '77-'78 only. Better yet, dyno charts specifically for '78 13Bs. I want compare tall ports and channels to the earlier ones with or without reversed runners, seperate standard runners etc.
The idea to make several threads with specifc themes sounds good, if I can be arsed to do it.
I can only post substantively about what I know about the parts I have, of course. There will be very little 2nd gen content. lolOh, I do have one picture of the GSL-SE core before it was torn down.
Looks like any other GSL-SE engine from the outside. Probably the only way to tell which set of ports it had is to look into the rotor housings. Not a very easy task most of the time, as you can imagine.
What do you mean by the bridge groove thing? The J-spec carb spacer had a bridge cut between both primaries, and must have worked alongside the channels in the manifold some how. The carb spacer is currently on my Cosmo and the idle and low end are decent. Should I steal it for the baja?
Does anybody have old reference dyno charts of HP and torque curves for stock REPUs, RX-4s, Cosmos etc? Oh, and an RX-3 SP thrown in for good measure? Even though it's a 12A, the SP should have a channeled manifold or a reversed runner manifold, being availiable in '77-'78 only. Better yet, dyno charts specifically for '78 13Bs.
I want compare tall ports and channels to the earlier ones with or without reversed runners, seperate standard runners etc.
Last edited by Jeff20B; 10-31-06 at 09:30 PM.
10-31-06, 11:32 PM
#24
All my parts are US spec. The bridge I was refering to is the channel at the top of the intake mani under the carb that links both primary intake ports. If there is no channel between the primary and secondary runners under the carb, then the secondary runners, which could be ported, along with the irons, are effectively shut off to any air flow until the secondary butterflys open.
My thought process/reasoning is that by keeping the primary intake runners stock and narrow in cross-sectional area, even if the center iron has the tall ports, the engine will develope a higher air flow velocity through the runners themselves. Now I may be wrong, but isn't that the best way to improve torque, as long as the cross-sectional area isn't too small? i.e., more vacuum yields better hp/torque, particularly in carb applications for better fuel mixture and atomization. At this point, the only porting I would do on the primarys with the tall port center iron would be to smooth the transition point where the intake mani meets the center iron. If done correctly, it should improve the venturi effect.
Since you are thinking of experimenting with more than one rebuild, you might try leaving the primary ports alone on the 1st build, do the secondarys only, then smooth the transition on the second build to see what difference it makes.
I find the idea of the reversed runner intake interesting. That would indicate to me that Mazda was trying to lengthen the primary intake runners to increase torque, much like the aftermarket wrap around 2-barrel intake manis do. If one were to use the tall port center iron and the shortest port end irons with the reverse mani, that might produce the most torque of all.
Afaik, all SE housings are US spec, we got the 13B, the rest of the world got the 12AT.
Well, I suppose it's time to get off my butt, go move the widebody and start cleaning up the shop so I can tear down the SE engine. If I don't, I'll sit here and eat all the candy I bought and didn't have a single knock on the door tonight.
My thought process/reasoning is that by keeping the primary intake runners stock and narrow in cross-sectional area, even if the center iron has the tall ports, the engine will develope a higher air flow velocity through the runners themselves. Now I may be wrong, but isn't that the best way to improve torque, as long as the cross-sectional area isn't too small? i.e., more vacuum yields better hp/torque, particularly in carb applications for better fuel mixture and atomization. At this point, the only porting I would do on the primarys with the tall port center iron would be to smooth the transition point where the intake mani meets the center iron. If done correctly, it should improve the venturi effect.
Since you are thinking of experimenting with more than one rebuild, you might try leaving the primary ports alone on the 1st build, do the secondarys only, then smooth the transition on the second build to see what difference it makes.
I find the idea of the reversed runner intake interesting. That would indicate to me that Mazda was trying to lengthen the primary intake runners to increase torque, much like the aftermarket wrap around 2-barrel intake manis do. If one were to use the tall port center iron and the shortest port end irons with the reverse mani, that might produce the most torque of all.
Afaik, all SE housings are US spec, we got the 13B, the rest of the world got the 12AT.
Well, I suppose it's time to get off my butt, go move the widebody and start cleaning up the shop so I can tear down the SE engine. If I don't, I'll sit here and eat all the candy I bought and didn't have a single knock on the door tonight.
10-31-06, 11:54 PM
#25
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Originally Posted by Jeff20B
Hey those rotor housings look familiar.
Chances are they're J-spec like that one you asked about in the picture. Your engine could either be a stock never opened, or maybe it was rebuilt at some point.
Can you tell me what the top of the intermediate plate looks like? Your three choices are:
1) machined flat with two threaded holes
2) not machined with casting flash visible
3) a cover plate over an EGR port, or just any cover plate
A yes on one of those three will narrow down the possibilities significantly.
Also, if you could tell me about the heater core fitting in the lower right of the picture, maybe I could narrow it down for you some more. Does it have a 6 point hex? Or is the rubber hose butted all the way against the plate?
Is there an oil pressure sender hole under the oil filter pedestal in the usual place? Perhaps with a little allen head plug? Or just a blank casting? Note it is just to the right of the temp sender out of view in your picture.
Look around the intermediate plate for R, R5 or NO up near the PCV breather tubes.
Edit: if the intermediate is a Y, look on the front side down near the spark plugs. I think it will be partially obscured by the rotor housing if I remember right.
Chances are they're J-spec like that one you asked about in the picture. Your engine could either be a stock never opened, or maybe it was rebuilt at some point.
Can you tell me what the top of the intermediate plate looks like? Your three choices are:
1) machined flat with two threaded holes
2) not machined with casting flash visible
3) a cover plate over an EGR port, or just any cover plate
A yes on one of those three will narrow down the possibilities significantly.
Also, if you could tell me about the heater core fitting in the lower right of the picture, maybe I could narrow it down for you some more. Does it have a 6 point hex? Or is the rubber hose butted all the way against the plate?
Is there an oil pressure sender hole under the oil filter pedestal in the usual place? Perhaps with a little allen head plug? Or just a blank casting? Note it is just to the right of the temp sender out of view in your picture.
Look around the intermediate plate for R, R5 or NO up near the PCV breather tubes.
Edit: if the intermediate is a Y, look on the front side down near the spark plugs. I think it will be partially obscured by the rotor housing if I remember right.
And yes the heater core hose has a hex end. You can see it in the second picture as well as some oil line down towards the bottom of the motor.
Last edited by MtotheIKEo; 11-01-06 at 12:00 AM.