i like the reverse manifold, cause that makes the secondary runners shorter, which is prolly counteracts the not as good flowing port runners.

 

Yeah, they gotta be good for something.



I've never actually driven a Cosmo manifold on a stickshift that flowed correctly (it's always been with the REPU engine and the stupid NO plate). I can't remember how it drove on my Cosmo with the automatic since I removed it several years ago before it ran right. All I know is the primary power didn't change much and since I upgraded the ignition, the secondaries now add a lot. It really gets up and moves at higher RPM but takes all day to get there. Converting it to a manual 5 speed is my summer project.



I just went through some old posts about manifold ports and Carl thinks the short port 3B intermediate plate will have great low end. It will work better than a tall port plate. This is encouraging since I want to use all three 3B plates in the REPU and junk the NO plate. He and heretic say that a small mismatch of .040-.060" from manifold to side plate is fine. I'm going to check the mismatch of a '74 manifold with the 3B intermediate right now...

 

I broke out the digital caliper and it came out to .07"



Next I'd like to post some pictures.

 

it depends on which way the mismatch is. the 81-85 12a, with the tall port center, has a big mismatch, intake is small, tall ports are well, tall... so like if the manifold is smaller, eetz steel good

 

Exactly. I got about 1.294" on the manifold and 1.381" on the iron. It's not much, but it's enough.

 

Ok I took some pictures. I posted them on the other forum because I wanted to save room to show off the build of my projects here. These pictures are just general curiosities anyway. You might get a kick out of them.



http://www.rx7club.com/forum/showthread.php?t=635642

 

i should take a couple pics of the jc cosmo housings, and my X housings.



cosmo looks like a NO primary, and a 74 secondary....



X just looks like 74-75 ports, but its an X casting!

 

Are talking about the 13B or the 20B? Do they have the same size ports on the inside?



Yes you totally should take some pictures. Especially the X casting!

 

13b cosmo and 20b are the same port wise.

 

Ah, I figured as much. No wonder the 20B has such great low end. Small ports, long runners...