trochoid

iTrader: (6)

I have used both the weld nub and the screw trick to remove the roll pins. I always try the screw first, the weld nub tends to blow out a little bit of the aluminum around the pin.

Jeff20B

iTrader: (13)

Cowering in the corner, as usual when I get all technical lol. Actually, I've wondered that myself. I wanted to talk to him about rotary powered VWs. He recently did a 20B in a customer's sand rail. I have a 20B and a baja...

IanS

iTrader: (4)

This is some really good info, especially with the pics. One question though. You are comparing US and Japanese engines, but what about Europe? Were any of the housings/ports/anything different on a european rotary? I wonder how many variables there are.

Jeff20B

iTrader: (13)

Paul Yaw says EU ports close at 50° and US close at 40°. I think '74 spec ports close at 50° but I've never measured them. They are between US-spec and streetported so I just assumed.

j9fd3s

iTrader: (3)

the euro 12a's also had larger exhaust ports, n210-10-100, people were using em in pro7 and it cars for a while, its worth something like 10hp...

j9fd3s

iTrader: (3)

oh and just to add a little documentation.... little list of the rotor housings i know of, all are usa spec unless noted

10a r100 usa 2359-23-055
12a rx2/3 2090-23-055
12a PP round port housing (??-1979?) ???
12a PP D port (79-current) 4352-10-100
1881-10-100a/3625-23-050 74-75 12a rotor housings
8871-10-100/150 76-79 12a
8341-10-100/150 80 california spec 12a
n201-10-100 81-83 usa
n249-10-100 84-85 usa
n210-10-100/150 (81-85?) euro 12a housings
n236-10-100? 12a turbo housings

4801-10-100 13b mfr PP housing
1757-10-100a 74 13b
3775-10-100 75-76 13b
8712-10-100a/150a 76-77 13b
8736-10-100a/150a 78 13b w egr
n304-10-100c 84-85 gsl-se

Jeff20B

iTrader: (13)

Interesting info. My Cosmo was made in 11/75 and sold as a '76 model. That explains the different part numbers for 3775 '75-'76 rotor housings and 1757 for '74 (and '75) rotor housings.

Now I'm curious about the exhaust sleeves in my Cosmo. I hope they're round like the '76-'78 engine pictured above, and not curved like the worn out J-spec with the oval casting covering 'Automobiles'.

j9fd3s

iTrader: (3)

i can look in the book monday, but it looks like theres a split in 75...

Jeff20B

iTrader: (13)

That would explain the difference in REPU and Cosmo rotor housings.

Jeff20B

iTrader: (13)

trochoid, any luck getting pictures of your GSL-SE side plates?

trochoid

iTrader: (6)

Working on it, have another project to finish up tonight, I'll have them up tomorrow, along with S4 NA and TII plates for comparision. Do you want the S3 12As with them for a side by side shot?

j9fd3s

iTrader: (3)

RX4 switches from 1757-10-100a to 3565-10-100c 10/74...

76 rx4 is 3648-10-100/150, 76 model year starts aug 1975

Jeff20B

iTrader: (13)

trochoid, it would be great to set them side by side like I did. Maybe your camera angles will be better aligned than mine were.

Mike, do you know how long the REPU kept the 1757 rotor housings?

Jeff20B

iTrader: (13)

trochid, any pictures?

Carl, care to add your take on reversion?

Thanks guys.

Nicholas P.

iTrader: (1)

I am deffintly learning alot here. So confusing, but so intristing.

trochoid

iTrader: (6)

OK, finally pics. Some are a bit fuzzy, didn't steady the camera enough. A few notes. I'm suprised how big the 12A pimary ports are, intake and rotor side, compared to the others. The NA S3/4's have the same size 6th port sleeve, but on the rotor side you can see the S3 port opening is a little shorter than the S4. Width is about the same, the depth of the pic makes them appear different. Same with the TII secondary port, it is bigger than the 12A.

It would be nice to have more old school irons to show, but almost all of my engines have been S3/4's. There aren't any old schools in town, afaik, the REPU is the only pre-7 rotary in town and it came engineless.


Primary ports.








Secondary Ports.

1badFB

iTrader: (1)

Beautiful!!!!!

Im lovin the side by side comparison shots, this is a very useful thread!! I love seeing how the design has evolved, and the changes that have been made.
I dont seem to recall seeing such comparisons before, It almost makes me think a simple thread on internal differences would be usefull... *wink wink*
...Just because this stuff is interesting on its own, and doesnt need any irrelevant questions about the changes of the housings.
What do you think Dr. T? haha

Im gonna have to go back now, and re-read everything to make sure I havent missed anything before this thread gets too giant.
Good work guys!

Jeff20B

iTrader: (13)

Thankyou for posting some side by side pictures.

Jeff20B

iTrader: (13)

Here is a 6 port 12A intake manifold. Notice how small the ports are?



My friend has a complete 6 port 12A sitting in his garage. It's complete from Nikki to special header-like cast iron exhaust manifold. I'm curious to see how it runs. I'm also curious whether swapping to a Y intermediate and GSL-SE side plates would beef up its power potential, or if it would hurt performance. I'm also curious to see how big the exhaust ports are and their timing.

Oh man, brain storm. If had a street bug, that engine would be excellent. Hmm, it would probably be great in a baja too with all that low end potential. That is, suspected low end potential. I have a sneaking suspicion the intermediate plate is of the hated NO variety. Maybe that's where they all came from? It had a gaping hole on top of the intermediate plate...

trochoid

iTrader: (6)

Does that gaping hole have a port to both primary runners? That's for the egr valve. Note my pics of the intake ends of the intermediate plates. The S4 NA iron has what looks like a round hole that's plugged, that iron has 'the gaping hole' for the egr. The rectangular holes on the other irons are the exhaust ways for the egrs that are mounted on the intake manifolds.

Those ports on the 12A 6-port intake mani are tiny. With operating auxillary ports, the low end should be quite good. You may need to go with the smaller intermediate ports for the best low end. Might make an interesting combo. The aux ports are butterflys, aren't they?

I can post a pic of the top on the S4 NA iron if you want.

Jeff20B

iTrader: (13)

The gaping hole on top does have two small machined holes all the way down to the primary runners. If you install a block off plate, there is no way for exhaust to communicate with intake. The NO plates have a freeze plug below the primaries just like an S4 NA plate. The port size and timings look practically identical too.

I don't know about the aux ports at this point. I know EU-spec 13B 6 ports had butterflies. I suppose I'll have to come up with a really great application for my friend's engine before he'll let me tear into it for a rebuild. It has excellent low end potential and most likely better high end than a common 12A. We just need to figure out a really great home for it.

Hmm, in a baja, you're not limited by engine length to any great extent. Same with a Karmann Ghia, bus etc. However in a street bug, most people go with the 12A due to length. Of course it doesn't need to be a VW application. Even a 1st gen would probably do very well. Then again you can fit a 13B in them pretty easily.

Any ideas?

j9fd3s

iTrader: (3)

nope, i only have catalogs for 76 and 77

Rx7carl

Wow, alot to read and digest. Great thread. I'll add my small contribution.

As far as the intake manifold. The channels look good. I would suggest that you try and round the edges to keep the airflow from shearing when it passes through the channel. Also you can widen them some more if you want.

What I wonder is this. While Ive heard of these reverse runner manifolds, Ive never held one in my hands, nor the engine plate that it came on. Now Im not sure what the airflow capabilities of the intermediate plate ports are on that engine but on the 12A intermediate plates, the air flow is pretty wimpy compared to the outer plates. That wouldnt make for good secondary power. :angry:

Its kinda funny because the 4 port exits are identical on a 12A, and the intermediate plate ports are taller so you would think more airflow right? NOT! The reason I suspect is that the runners are narrow and have to make a very sharp turn into the port exit, much sharper than the secondaries. Deepening the runner bowl and shaving the bridge that seperates the ports to be as thin as you can stand it will soften the radius that the charge has to negotiate and increase the airflow.

But thats not what you were asking me LOL. Yes the mismatch will fight reversion BUT, in the forward direction the sudden increase in runner volume should cause a dramatic decrease in velocity. Thats not good for forward flow obviously and low forward velocity doesnt have much energy to keep the charge moving in the right direction and fight a reversion wave. I think the main way Mazda tried to stop reversion is the flares on the runners where the manifold interfaces. When you port an intake manifold you match it to the runner not the wider interface. Peejay and I had discussion about the tall ports and there was an idea of actually filling the top and bottom of the runners and blending it back to the manifold exit port. Of course you add in a step or flare to fight reversion. AFAIK no one has actually tried this so I dont know what the results would be.

Jeff20B

iTrader: (13)

Thanks Carl. Very informative.

So you're saying I should smooth the sharp edges of the channels and possibly make them wider? Would that affect high RPM more than low RPM?

I've only seen the outside of the intermediate plate on which the reverse runner manifold came stock. The only outward sign that sets it apart from other inermediate plates are the tall ports and a lack of an exhaust port. Also no freeze plug. Sorry, no pictures at this time.

As for the porting, the CD Cosmo was under the AP or Anti-Pollution banner and I'd bet dollars to doughnuts all four ports are the same size inside - the stock 12A size we all know. That port size with the reverse runner manifold would give the Cosmo decent low end on primaries while sacrificing some secondary power. That's ok for the type of driving the Cosmo would see.

Speaking of runner size vs carb barrel size, the seperate runner manifolds' runner size is roughly the same as the carb barrels. The channeled manifolds all had smaller diameter runners under a funnel shaped section directly below the carb spacer.

My J-spec manifold has this funnel section and narrow runners, but came stock on an intermediate plate with short ports and tiny ports on the inside, as seen earlier in this thread. Taking what you said, Carl, into account, it would seem Mazda was trying for extremely low reversion with this particular setup. Most likely for respectable low RPM torque. Perhaps even as good as an RE-EGI (GSL-SE) engine some 10 years before.

The mystery J-spec engine consisted of:

Hitachi carb with 90/140 fuel jets and 90/160 air bleeds. Carl, you know Nikkis but the Hitachi is similar enough to compare. The small jets and large air bleeds tell me the carb was set up mainly for low RPM operation. I tried it in my Cosmo and it sucked for power from mid to high RPM before I tried a jet and bleed swap. Now just the high end is weak, but I haven't messed with the secondaries much yet. It's now 100/145 jets and 60/90 bleeds. I can go up a few more sizes in fuel jets but my Cosmo carb was happy with 60/90 air bleeds so I copied. What are your thoughts on this?

The manifold had narrow runners, channels, and a funnel section. The carb spacer had a channel connecting both primaries.

The intermediate plate had short ports. The primary port timing was no larger than a GSL-SE or NA S4.

The secondary ports were stock 12A size inside and out.

The exhaust ports were identical to GSL-SE with later opening and closing than 12A and US-spec 13Bs in the '70s.

The themrostat was 190°F with an internal full-time bypass in the bypass hole. I may be able to get a picture of it today. This meant HOT running.

The spark plugs were points type B6ET. The number 6=rather hot heat range.

Automatic counterweight. Must have been on some luxury car in Japan.

Carl, since I want more performance out of this and cooler running, plus it will be on a stickshift, but I still want a fair amount of low end torque, what parts do you think I should use? Right now the choices are stock J-spec intermediate plate and a 12A Y intermdiate plate. No porting other than some internal smoothing to remove casting flash and sharp 90° edges. The port timing will remain stock.

My preference would be to use the 12A Y plate because it weighs noticeably less, and my Cosmo is doing well with a regular runner manifold with no channels on its tall port intermediate. I have plans to either swap in a channeled manifold or just a carb spacer with channels connecting primaries to secondaries on the Cosmo. It's currently using the carb spacer from the J-spec with channels connecting both primaries only. I intend to swap back so the J-spec can have its spacer back, and feel the other spacer with primary to secondary channels will take the place of a channeled manifold. Maybe. It's easier to swap spacers than manifolds.

Carl, I've described the J-spec engine as well as I could. I guess what I'm asking you is this: Do you think I could get away with a 12A Y intermediate plate while everything else remains stock on the J-spec engine? Do you think the tall ports would kill flow? Do you think the greater port timing of stock 12A ports would ruin low end potential? My Cosmo seems to say otherwise, but it's fairly different in some ways and somewhat similar in others. Oh, and the waterpump will be FC with a 180° thermostat for further weight reduction and cooler running. Of course the ignition will be upgraded... you know me.

Jeff20B

iTrader: (13)

I've got some pictures to show you.

The waterpump with the strange object in the bypass hole is from the J-spec engine. It is spring loaded to always be in the up position, unless the waterpump is running, which will pull it down and allow coolant to bypass regardless of thermostat position/temperature. Why would Mazda do that?


I'd like to use this S4 T2 waterpump because it has an undrilled casting next to the EFI water temp sender. I can tap this casting and install an electric water temp sender while keeping the stock temp sensor for possible future EFI use. It's also lighter than the stock cast iron waterpump.


The Exhaust flange I plan to use. I got it from Mazdatrix (notice it lacks the RB).


Here's the '78 RX-4 manifold. It is very similar to the J-spec manifold, except it is lighter and the funnel is entirly cast as opposed to the J-spec where it had to be machined. I feel the rough surface of the casting will prevent fuel-wetting moreso than the J-spec.


It just needs some paint stripper. Notice the channels in the spacer? I wonder why Mazda did that.