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Naturally Aspirated Performance ForumDiscussion of naturally-aspirated rotary performance. No Power Adders, only pure rotary power!
From the "12A" to the "RENESIS" and beyond.
Who if anyone makes bolt on intake manifolds to facilitate ITBs on a NA 13B?
I'm most likely interested in a quad throttle body setup instead of dual throttle bodies.
Yes, I'm considering injection over carbs... So much for keeping it simple.
I want to figure out my intake setup before I decide my irons as I may be restricted on iron selection depending on the intake port configuration (4 port, 6 port, etc.) of what's available there for ITB manifolds.
AFAIK nobody makes ITB manifold anymore. Anything you can find is a Weber manifold.
I cheated and used a modified Holley 750 as a throttle body on a Racing Beat intake manifold, which is like having 42mm ITBs, but it isn't ideal. Next best is the TWM DCOE manifold I have, which has a much nicer port volume with the throttles about 3" from the engine, but it still won't be ideal because it is designed around DCOE port spacing.
Laird (?) made a beautiful ITB manifold in Australia that all of the Improved Production racers raved about. Apparently they were making well over 300 horsepower from a non relieved bridge port (no part of intake port may pass through rotor housing, so no reliefs)
IMO unless you are racing, I would not bother. Until you get to the real pointy end of the obsession curve where you are optimizing every dimension of cross sectional area and runner length, the main benefit of ITBs is throttle response.
As above, you could join the IPRA mob (facebook mostly now?) and ask if anybody has a Laird manifold. Used to be like hen's teeth, but with rx7s mostly uncompetitive now, some might be available. Do know someone in sports sedans here who fabricated his own 4 port manifold for an REW, basically just 3/8" 6061 plate and aluminium donuts, which I'm sure a reasonably qualified fabricator over there could accomplish too.
As a very long shot, but don't think Xtreme has dealt with the public for a decade now, I remember they had something that appeared to me to be a motorcycle 4cyl TB mounted on a casting.
you either want to keep them all separate or pair the primaries and pair the secondaries separate from the other.
the manifolds that pair the primary and secondary together are all crap imo. They have to be different diameters and/or lengths for that to work effectively, which will vary for NA vs FI. Which those manifolds aren’t.
Different opening timing too for a broad powerband. The Renesis intake manifold being the premier street example, and the 767B sliding trumpets being the premier individual-runner race example.
Don’t be afraid of making your own custom one either. Flanges are now easily ordered lasert cut online etc.. Here’s a custom REW turbo that was built by Tripoint Engineering back in the day and was quite effective for competition use. I’m still trying to figure out how they were able to mandrel bend the oval primary runners smoothly. The secondaries are round tube and oval formed at the engine flange.
. . .
per my previous comments I’m confident it can be improved upon, which is why I bought it.
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you either want to keep them all separate or pair the primaries and pair the secondaries separate from the other..
No you do not, and I cannot emphasize enough how bad this is. The vacuum in one port when the other port sees pressure from port reversion or vice versa will cause the airflow to ping pong instead of flowing into the engine, and exhaust reversion will skyrocket. Mazda did it on the EFI intake manifolds which also had extremely long runners, and the engines had extremely conservative port timing, you do not want to do this on a short runner manifold or anything with decent ports.
I have done it. It sucked heavily.
If you must pair runners, pair the ports of a given rotor. Do not ever have different rotors sharing a throttle blade.
That REW manifold looks like hot garbage, the runners are way too small, have no taper, and curve right before the engine instead of leading out a few inches from it. It might be fine for a turbo application where you can cover up the horrible flow with more boost.
it uses bike ITBs to a custom manifold which you can do right to the block or from the stock LIM. looks promising but I haven't test it myself yet - the FB page is more active or available if you need to message him.
pics are kind of scarce, but the Lake Cities style intake works great. it looks like it would only make top end power, because its so short, but in real life it was 2000-7000rpm.
i feel like getting rid of the 90 degree bend, helps a lot.
Hey, I know that pic! That's about a third of my rotary intake manifold collection. And the R53 Mini that I'm about halfway into finishing the Subaru drivetrain/suspension swap.
The one on the right is a TWM for a 4 port 13B (aka '74-78 style), the one on the left is an Atkins manifold for a 6 port 13B, the one with the Dell'Orto DHLA attached is a Lake Cities manifold for a 12A. That mess of linkage that I'm building is in the more or less exact location of the stock Nikki primary throttle shaft, relative to the engine, so I can use the stock throttle cable and OMP arm. Still have not gotten enough round tuits to figure out how to stick the TPS on it so the solenoid rack works correctly for vacuum advance, or how to integrate the crankcase breather and evap system.
I see "Atkins" clearly cast into the Left manifold now.
Here is a pic of the TWM twin manifold with injector throttle bodies.
This is closest to the mental image most of us probably conjure into our heads when we hear "ITB".
good, because Atkins is trash. they sold me their side draft that was so poorly made I needed to get it machined and welded for it to work and when i approached them about it I got crickets. One part was bad packaging and other parts damaged the gasket the other was that the stud hole for the carb was bad and was going to cause a vacuum leak. Atkins sucks and they're just a re-seller for mazda parts, you should be racing your mazda and getting it from mazda - cut that middle man **** out
Don't forget Atkins also sells the knock off Mazda stock parts they developed as actual OEM Mazda parts.
You order the Mazda part and get the fake even though they claim to sell both fake and real Mazda parts.
wow I had no idea they were actually ripping people off like this, thats awful. such a terrible company, I happily drag their name through the mud any chance I get.
I spent a lot of time over the years away from the forum but still very much rotary interested and had the pleasure of picking the brain of the late Rick Engman. I wish I'd have had more occasions to get out there before he passed. He confirmed a few of my suspicions and educated me in other ways. I got to see a few neat custom projects that he had done for Jim Downing's engines that he wouldn't let me take pictures of. One thing we discussed was throttle bodies. Rick was not a forced induction person. He was a non-turbo race rotary builder and a damned good one. If it was a peripheral port engine, he always had a throttle plate per rotor, as is typical for peripheral port engines. However, things got interesting for non-peripheral port engines. He always wanted the primary and secondary ports to open and close at the same time. This was optimal to making power and the actual reason why 4 port non-turbo engines make better power than 6-port engines. It has nothing to do with the flow through the end housings as most believe but rather the fact that the primary ports close much sooner than the aux ports. This does create an interference wave in the intake manifold that hurts power.
In order to try to mitigate that and get some useful interaction, if you have primary ports that close earlier than the secondary or auxiliary ports, if present, a separated manifold in which the primary runners merge and the secondaries merge is the best option. Case in point, the Renesis. If you have primaries and secondaries that close at the same time, he merged both ports from a rotor together to use a single throttle plate per rotor. In other words, Weber style. He did not believe in 4 plates on a 2 rotor as the primaries and secondaries flow different amounts and would require differently sized throttle plates to function correctly, something no one does. I did see Paul Yaw do this with 2 throttle plates on 1 rotor about 25 years ago for an airplane. He made the same power and it was simpler and easier to setup and tune. Rick did have a neat engine that did have an 80 deg closing primary port along with 6 port end housings on a Weber style tb that made some crazy power with an 8500 rpm redline. It was very creative how he did it. Keep in mind that if you go forced induction lots of things change.
You need to think about everything together as a package and not just which engine and which intake and which exhaust, etc. It all needs to work together and be chosen as a single unit.
I spent a lot of time over the years away from the forum but still very much rotary interested and had the pleasure of picking the brain of the late Rick Engman. I wish I'd have had more occasions to get out there before he passed. He confirmed a few of my suspicions and educated me in other ways. I got to see a few neat custom projects that he had done for Jim Downing's engines that he wouldn't let me take pictures of. One thing we discussed was throttle bodies. Rick was not a forced induction person. He was a non-turbo race rotary builder and a damned good one. If it was a peripheral port engine, he always had a throttle plate per rotor, as is typical for peripheral port engines. However, things got interesting for non-peripheral port engines. He always wanted the primary and secondary ports to open and close at the same time. This was optimal to making power and the actual reason why 4 port non-turbo engines make better power than 6-port engines. It has nothing to do with the flow through the end housings as most believe but rather the fact that the primary ports close much sooner than the aux ports. This does create an interference wave in the intake manifold that hurts power.
In order to try to mitigate that and get some useful interaction, if you have primary ports that close earlier than the secondary or auxiliary ports, if present, a separated manifold in which the primary runners merge and the secondaries merge is the best option. Case in point, the Renesis. If you have primaries and secondaries that close at the same time, he merged both ports from a rotor together to use a single throttle plate per rotor. In other words, Weber style. He did not believe in 4 plates on a 2 rotor as the primaries and secondaries flow different amounts and would require differently sized throttle plates to function correctly, something no one does. I did see Paul Yaw do this with 2 throttle plates on 1 rotor about 25 years ago for an airplane. He made the same power and it was simpler and easier to setup and tune. Rick did have a neat engine that did have an 80 deg closing primary port along with 6 port end housings on a Weber style tb that made some crazy power with an 8500 rpm redline. It was very creative how he did it. Keep in mind that if you go forced induction lots of things change.
You need to think about everything together as a package and not just which engine and which intake and which exhaust, etc. It all needs to work together and be chosen as a single unit.
07-23-23, 04:19 AM
