Jeff20B

iTrader: (13)

Oh NOes! You have an NO plate lol. Man, I feel sorry for you. I really do.

You're missing out on a ton of power. Or at least that was my experience (and part of the inspiration for this lengthy thread). The good news is you can upgrade to a commonly availiable Y plate from a forum member here and it's almost fully compatible with your other plates (may need one tension bolt hole plugged). Just put the word out that you're looking for one for your next rebuild. I picked one up from my local rotary shop for around $20 before he sold all his extra parts to Atkins/got rid of them.

If I can find some time today I'll take some pics of my NO plate and some of my small ported GSL-SE parts.

Here's some trivia for you all. The NO plate is only compatible with '70s rotor housings which have a small machined bridge allowing coolant to flow through the stagnant water jackets at the top of the rotor housings. I know '74 REPU rotor housings are compatible. Not so sure about the suspected J-spec housings you have there. I'll check mu housing and get back to you.

The reason for the channels is because the top of an NO plate contains an EGR port which blocks a some of the water passages. I'll show you what I'm talking about as soon as I can post some pics...

Oh, and before I forget, try to take the upper inspection cover off of your rear plate and look down. You should see an R5 like this.

Try to look for some undrilled tension bolt castings too.

It also looks like your rear plate lacks an oil pressure sender like my plate. That's why they added one to the banjo bolt on the oil line below. It's fairly common.

trochoid, having different port timings is one possibility, and it may work with channels as well as the primary bridge because that's how the J-spec engine was. It had short NO size primary ports and taller 12A size secondary ports. The 3B ports are actually horizontal at the top and the Y plate will be ported to '74 spec which will allow for a slant from the standard size up to '74 spec. I read somewhere that a slant is better than straight for flow. IT was just one person's opinion though.

I don't think I'll touch the manifold porting at all. Too many stories of botched attempts. I want them to still be backwards compatible.

Yes, the reversed runner manifold should porovide the best torque of all, but I've modified it a lot on the outside, removing the ACV casting, and it now goes in and out of the MG without needing to pull the engine. It's staying. A normal manifold hardly fits and I don't want to cut into the car.

I believe the reversed runner manifold was Mazda's way to make the Cosmo perform decently. Then they found that they could combine the tall ported intermediate with an earlier normal manifold, but with channels added, with great results, so they kept producing it; the '78 RX-4 for instance.

The SE, yes, but not the RE-EGI engine itself. They also came in the Luce or Cosmo. I just would like to see which set of ports the US-spec engine recieved because I don't know the history of the 'GSL-SE' engine I tore down a few months ago. It could J-spec or US-spec. I really don't know.

I'll try to get some new pictures up for you guys.

MtotheIKEo

Thanks for all the help so far Jeff. Im just really trying to identify exactly what I have so in the future (hopefully not too soon) when I need to buy rebuild parts or anything for it I know what I have.

Naegleria_Fowleri

This thread needs to be stuck like mad ****.

2wankel

iTrader: (1)

Jeff20b great thread. Questions on exhaust porting, The stock exhaust is rectangular in shape, yet Racing Beat has the top and bottom of the exhaust rounded. Why not make the rectangular exhaust larger and keep it near stock opening?

Racing Beat Race Exhaust port.




RB exhuast port template




Here is an example of BDC's exhaust port they are more rectangular than Racing Beats exhaust ports. I really like these better because it keeps the stock shape. From what I read if the exhaust ports open early, you loose torque and if it closes late you get overlap. So does this mean that this shape is more efficient for the street than the Racng Beat exhaust port?

BDCs exhaust port



Racing Beat bridge port and exhaust port template next to stock 87-88 TII exhaust









keep this thread going its great

thanks

rotarygod

iTrader: (1)

Jeff one thing to consider when trying to figure out why certain ports have different timings is that at some point in the early 70's, the outer ports were the primaries and the inners were the secondaries. Unfortunately I don't remember exactly when. That would explain why the "secondaries" appeared smaller in one engine.

As far as each intake manifold is concerned, just by looking at them I'd think the one that stays completely separated would be better for low end and have less top end. The one that has adjacent runners connected should have less ultimate low end but make more top end. "Should" is the key word here.

trochoid

iTrader: (6)

2wankel

From what I have been able to gather/interpret, though no one has come out and said so directly, I think the top and bottom of the exhaust ports are rounded to reduce the shock load on the apex seals. All of the exhaust porting I have seen widens the port which leaves more of the apex seal hanging out in mid-air and less of it supported on the ends. Since part of the point/result of porting is increasing the powerband into the higher rpm range, the apex seals are subject to more centripital forces and bowing out.

By rounding both the bottom and top of the wider/taller ports, this allows the seal to make a more gradual bow out, then bend back in flat. This spreads the instantaneous shock load over a longer time frame and spreads the stresses across the length apex seal that is exposed to the port, instead of concentrating all of the bending/shearing forces on the seal at the fore and aft edges of the port.

I have seen an apex seal that had the center part of it chunked out. The seal didn't break in two, it simply lost the outer half of the seal, the exact width of the exhaust port.

Directfreak

iTrader: (2)

Hey guys - please PM me when to place this thread in the archive. I don't want to put it there while people are still contributing to it. It's very interesting reading.

Jeff20B

iTrader: (13)

MtotheIKEo, could you post a pic if the top of your intermediate plate?

I checked my J-spec rotor housing and it lacked the little coolant passage. Only the '74 housing had it. If your housings lack the passage, some of the water jackets at the top of your engine aren't flowing.

2wankel, according to Judge Ito, the flat closing edge of an exhaust port is better for turbos and is more peaky than the round edge. It's also best to have a slightly rounded opening, as the RB templates do (although it's kind of a lot, but then they are technically for racing).

BDC's ports are great for turbos. He's really into the half bridge stuff too. That is, the primaries are streetported and the secondaries are bridged. All this with T2 plates.

rotarygod, I haven't actually torn into my Cosmo's engine yet, but when I do, I bet the outer primaries will be the same size and the intermediate secondaries as far as port timing is concerned. It's just an educated guess.

The reasons you gave for the possible better low end torque of the seperate runner manifolds is intriguing. Granted I've never actually tried a channeled manifold in my Cosmo. I've only tried a channeled manifold in the RX-4 and REPU (both of which were streetported). Both appeared to have adequate low end, but it is like comparing apples to oranges.

I'm just using Mazda's example of always combining a channeled manifold with tall intermediate ports and never the other way around. All '79-'80 RX-7s and the flapper valve '81-'85 models for instance. Not to mention the late '70s RX-3s and 4s (maybe the Cosmo too). Of course there are some exceptions: the tall ported Cosmo with unchanneled reversed runner manifold, and the short port J-spec with channeled manifold. The J-spec was set up entirely for low RPM operation. This of course means the carb, manifold, port timing, thermostat, and spark plugs have to perform at their best in a limited RPM range and provide a graciously wide torque curve throughout, which I suspect they did quite well. I've since rejetted the carb and tested it on the Cosmo and RX-4 with various porting and it did pretty well down low. Only the secondaries felt weak because I mainly concentrated on the primaries.

I wonder where Carl is? I wonder if anyone out there has ever dynoed the various manifolds in question.

MtotheIKEo

The intermediate plate is the plate between the two rotor housings right? Sorry Im new to this. When it stops raining Ill unbolt the rats nest and see if I can get a couple pics.

Hyper4mance2k

iTrader: (40)

That's how I do it!
http://www.nopistons.com/forums/inde...howtopic=63787

trochoid

iTrader: (6)

OK, here are my housing pics. It will be a couple of days before I can get irons prepped and ready for pics. Unfortunately I don't have any of the irons to go with the 74-78 13B housings.

In this series of pics, I set them up with the older ones on the left side, newer ones to the right, with the exception of the lone 12A housing that is the left one in all of the pics that show all 5 housings. While not 1st gen parts, I included both NA and TII S4 housings to show a couple of differences. If you look at the NA exhaust port, you will see a baffle, which is not in the TII housing. The baffle was Mazda's method of quieting down the NA exhaust note. It's not needed in the TII because the turbine blades do a better job of quieting the exhaust down. So much so that one can run a less restrictive straight though exhaust on a turbo engine, and still have it be quieter than the NAs.


This was the first time I have ever set the different housings side by side and noticed some interesting differences. The 12A and 74-78 13B exhaust ports appear to be the same size, along with the sleeves. I have not measured any of them, I will try to do that tomorrow. If you look closely at the pic that shows outside view of the ports, the outside diameter of the sleeves is smaller than the SE and later ones. The oil injection ports, which began with FI engines. are different. On the SE housing, the port is lower than the S4s and the hole on the inside of the housing is bigger. They all have a removeable jets, similiar to the ones in the e-shaft. I have not measured the orifice size to see if there is a difference, I don't have the index bits for that, but reading the FSM for the different years, there is a difference in MOP output between the 3 different FI engines with the TII using the most oil injection.


First pic is the top showing how the logos have changed. The fine print casting of the license agreement is identical on all of them. If you can't read the cast letters just above the MAZDA on the 74-78 housing, it says AUTOMOBILES and you can see where the 13B was moved up. I'm not sure what year they changed the logo, Jeff probably knows, , but I'll venture a guess it was with the introduction of the 7.

As another side note, the little divots that are cast in the 12A housing, just above and on each side of the lower exhaust manifold bolt, is a left over from the thermal reactor/heat exchanger system before Mazda went to cats. One hole or the other was drilled out on the housing, never both. This meant the earlier engines had front and rear designated housings to match the hole to the thermal reactor/heat exchanger.

Next series of pics will show the differences of the exhaust ports on the inside of the housings.

trochoid

iTrader: (6)

Now for the insde of the housing exhaust port pics. I don't really have much to say about these. One of these days I will buy a degree wheel, figure out how to use it, and learn more about port timing for the exhaust, intake too if I decide to get carried away.

In the pics that have a scribed line, all of the ports opening and closing points start within the lines. The bottom line is a hair too high as the marker dipped into the 2mm bevel on a couple of the ports. Of course, the TII port is the largest, but oddly enough, the 12A and 74-78 13B ports appear to be the same height and have nearly the same beginning and ending degrees, the port is wider though.

If you look at the last pic, you may notice that the chatter marks seem to stop across the port opening and there appears to be a line above the port in the housing. This is most evident on the TII housing. Chatter marks are just that, the apex seal bouncing/vibrating on the housing face. The marks change over the port because the apex seal is bowing in and that changes it's vibration resonance. The line right above the end of the port is due to the seal hitting the housing harder, after it bounces off of the closing bevel. One can equate chatter marks to the washboard ridges/dips that asphalt pavement developes. The 'chatter' in the asphalt starts out small and keeps growing until it starts breaking up. Same thing happens to the chrome surface of the housing. Harder braking and heavier vehicles increase the washboard in asphalt, higher rpms increase chatter marks in the chrome. I have torn down engines where the worn off chrome pattern directly relates to the chatter pattern.

The deepest chatter marks, and the majority of the chrome wearing occurs from about 2" below the lower spark plug hole and the leading edge of the exhaust port. You will find very few if any chatter marks from the trailing edge of the exhaust port to the trochoidal bump, (the narrowest part of the housing), between the spark plugs. It's my opinion that the deepest chatter marks start and end where do because the apex seal cants in it's groove in the rotor from the pressure of the expanding combustion gases. This 'canting' changes the angle at which the seal meets the chrome surface. There's something for you folks to chew on.

Jeff, sorry for straying away from the torque issue, but since this thread will be archived, it only seems appropriate to me to provide as many little tidbits of trivia as I can. Most of your torque musings are over my head since the intakes you have, I have never seen and I am a visual person.

Jeff20B

iTrader: (13)

Very nice trochoid.

If I may correct you on a few points.

The thing in the 2nd gen NA exhaust port is generally called a diffuser.

The 13B housing with the MAZDA is a 3B housing. That is, it only came with 3B side plates. It mainly was available in '74-'75 REPUs and RX-4s but I think the '76 and '77 REPU also had it. The '76, '77 and '78 Cosmo and RX-4 went to the newer mazDa font with 13B right next to it.

Notice the port timing of your '74-'75 housing compared to your GSL-SE housing? The '74-'75 opens sooner and closes sooner. The GSL-SE opens later and closes later. That is the reason for the GSL-SE's excellent low end torque.

I recall you said your GSL-SE engine was definitely US-spec. That proves my GSL-SE core is actually J-spec, and the GSL-SE rotor housings I put into my bro's RX-4 engine are US-spec after all.

Please post some pics of your side plates next. I'll post some too.

Jeff20B

iTrader: (13)

oops

j9fd3s

iTrader: (3)

heres another one, from direct personal experience.

car is a gsl-se, stock intake, RB street port exhaust.

the FC intake ports are bigger, but i think the runners are the same, seat of the pants says the fc block is worth about 15hp@6500-7000...

Jeff20B

iTrader: (13)

Mike, it makes sense that the sooner opening slightly wider exhaust ports would gain some HP up high while taking it away from down low. I think it was Steve who said the GSL-SE had the best low RPM torque of any 2 rotor Mazda ever produced. That is to say it kicked in harder at a lower RPM than any other engine. I think we're finally beginning to see why. It's all about the exhaust port timing. Well, the intake is important to, but at least I can take advantage of identical exhaust ports in a carbed setup.

MtotheIKEo, the intermediate plate is the middle iron between the aluminum rotor housings. Try to get a picture of the top of yours.

To continue my pics from the other day, here is a different angle of the reversed runner Cosmo manifold. Notice the tall ports? They're tall because they're secondaries and only open at high RPM. They wouldn't flow worth anything at low RPM, and that is why Mazda kept them small in all normal runner manifolds.


Here are the coolant passages I was talking about. They're necessary if you want to use an NO intermediate plate.

Only '74-'75 rotor housings have them as far as I know. I think Mazda did this on these early housings for maximum compatability but stopped on '76+ except for the engines in which the NO plates came stock, whatever engine that may be (perhaps MtotheIKEo's).

How does a rare J-spec GSL-SE rotor housing stack up to a stock '74-'75 housing? It looks like the J-spec opens just a tad later and closes right around the same time, if not just a tad later. It's hard to tell from the apex seal damage and the carbon buildup.


These two open the same but one closes very gradually and actually sucks. This is the upside down D port that rotarygod warns against. I am going to do my best to correct it. I think T2 spec or a little later closing will work out fine. Basically whatever I can do to straighten the closing edge will be an improvement.


Here they are all lined up.

Jeff20B

iTrader: (13)

Maybe a line through them will show off their relative openings and closings.


From the spark plug side.


From the top.


Exhaust side.


My NO intermediate plate. Notice the cover plate over the EGR hole? The two water jacket positions are actually fully blocked (the very reason for coolant passages in the rotor housings). The port timing looks familiar.

This thing is just as heavy as the J-spec R5 intermediate, if not heavier. Probably due to more iron. It's all unnecessary weight. I won't be reusing this.

Jeff20B

iTrader: (13)

The outside ports of an NO plate. The mismatched outline you see is from when my Cosmo reversed runner manifold was on it in the MG. Even with a terrible mismatch, the MG still did pretty well. I can't wait to install an engine with correct tall ports to take full advantage of the secondaries.


Here's the rear plate of my J-spec GSL-SE engine. The main port is smaller than a typical 12A Y plate. At least it's bigger than an NO port. Too bad I can't show off the intermediate that came with this engine. You'd be shocked to see that it's even smaller than an NO port. Oh well maybe in a few months.


The angle is not quite right to compare it to the J-spec GSL-SE plate in the background, but at least we can see how similar the early J-spec is to an NO port. A US-spec GSL-SE should be the same size. Only the J-spec GSL-SE is smaller.


And here is the engine that came with the early J-spec intermediate plate. I'd say the tall port Y plate is going to be a major improvement. Wouldn't you?

MtotheIKEo

Jeff- Without removing the rats nest I cant really get a good picture of the top of the intermediate plate, but it does have that block off plate like your NO plate has. My housings also have these two ribs where as none of the other 13b housings pictured have them, so I you were correct about them being "early J-spec"

Jeff20B

iTrader: (13)

I think you're right about your rotor housings. Count on them having a funny exhaust sleeve like my worn out one pictured above.

Just so you don't get too confused, all 76-'78 13B rotor housings looked almost the same on the outside. Take this one for example. This is the other side of the engine pictured above. Notice how similar it looks?

It has the same mazDa font and the same unshrouded spark plug holes with the two ribs. But look closer. Look right where it says mazDa. It lacks the small wide oval.

Jeff20B

iTrader: (13)

Totally blank.


Your rotor housings have this small wide oval as does my worn out one.


So what is the point of the oval? It looks like someone machined away a word or something. I've seen it in castings before. This what I think it used to say.

This is one of the early J-spec rotor housings which I'll be using in the baja. Kind of ironic, isn't it. The exhaust sleeves look like the ones in the '76-'78 engine above (they don't have the funny curve in them) and the chrome is decent.

You may want to watch out for your exhaust sleeves when the time comes to rebuild your engine. If the chrome is still decent you could reuse your housings. It just might be a good idea to swap the sleeves for some '76-'78 sleeves if you can find some.

MtotheIKEo

Speaking of rebuild, if I need to order a seal/gasket kit for this motor, what would I order? Or just tell whoever I get it from what I have and let them sort it out?

And pardon my ignorance, but what are the exhaust sleeves?

trochoid

iTrader: (6)

Iirc, the older 13B 4-port gasket kits are getting harder to come buy or are NLA. The SE kit will work except for the intake gasket, which can be made out of good quality gasket paper.

The exhaust sleeves are the different colored insert that you see inside the exhaust ports. They can be removed and even changed, i.e., to make a 2nd gen NA housing into a TII housing, change the exhaust sleeve and the rear housing needs a hole drilled into the water jacket to feed the turbo for cooling. Removing the sleeves can be a pita and the engine must be apart to access the roll pins that retain the sleeve in the housing.

MtotheIKEo

Thanks Trochoid, I just read a little on them and someone recommended adding a little weld to the roll pins and then grabbing them with pliers. Just more information that I hope I wont have to use :x:

Hyper4mance2k

iTrader: (40)

This is such a Blake thread. Where is he at?