I am considering embarking on a N/A 20b FD project and I have been searching the forum for info and I have found many answers. That said I still have a question about the potential rwhp of the below set up:

Fully rebuilt N/A 20b,
bridgeported,
S5 9.7 rotors,
Msd Blaster ss coils,
Haltech E11v2,
Custom exhaust manifold 3-1(undecided on sizing)
Stock intake manifold and throttle body

vs the same but with custom intake manifold with 3 x 50mm individual throttle bodies (ITB).


I know that the ITBs are going to make for a more efficient/powerful N/A motor but I am wondering just how much difference it will actually make.

I really like the appearance of the stock 3 rotor intake. Whenever I imagine a 3 rotor engine I visualize the 3 rotor lettering on top of the manifold. Although ITBs do have there own visual appeal it seems to fit with more of a no nonsense racecar image. I would like to build a streetcar that can pass the odd inquiry by a cop looking under the hood. ITBs scream emissions violation.

If I can make 300rwhp with the stock intake I am inclined to proceed with the project.

Thanks in advance for your thoughts.

 

The throttle body and manifold inlet are the same size on the 13B-RE and 20B. If you ask me, it's way undersized for the engine. Numbers for N/A 20B's typically float a bit above 200 whp with the stock manifold. Gto-Rx7 had a setup similar to yours, with a custom ITB setup that made about 350 whp. I think that right there shows how restrictive the stock setup is.

I really think you'd be hard-pressed to make 300 whp with the stock intake manifold and throttle body.

 

Well after researching some more it appears that the performance advantage of ITBs is really worth it considering it only adds about 2k to the cost of the conversion while freeing up lots of power.

I guess I'll chop up the stock intake and mount the 3 rotor casting somewhere in the engine bay.

 

Should buy mine, it's already street ported, has a polished intake, ceramic coated front cover, brand new 9.7 comp rotors, also has a TEC 1 with high power coils (no MSD needed) and base fuel/ign map already done for you, motor mounts, brand new rotor housings, both center irons are new, lightweight flywheel, heavy duty clutch, etc, etc.

Save you a ton of time and money and I'd be happy to sell it without the manifolds, just the TB if you want as the EMS already has a GM TPS with a custom boss on it, plus if you didn't want other things we can discuss/remove to save additional money, etc.

https://www.rx7club.com/20b-forum-95/fully-built-20b-package-sale-593731/

PM me and we can talk more if you like.

 

I am sure you are offering a sensible option but part of the fun of a project for me is actually taking the time to do as much of it as possible by myself. For me that would include finding a motor, cleaning it, ordering parts etc. I don't plan on doing this too many times so I will try to enjoy the whole process. But thanks for your offer.

 

So strip it down and do a bridge port like you want. It'd save you a bunch of work since it's already street ported so the milling would be reduced. Reuse the seals and everything else and it's still "customized" by yourself, which would address that issue.

You could still order parts and keep them as backup in case the motor ever has a breakdown, issue, etc. Trust me, it's a whole lot easier to have things on hand than not.

Having gone through the do it all yourself side of things, it's certainly quite fulfilling to do that but it takes a lot of time, patience, and things do not go as you plan more times than not.

While I would love to work something out with you regarding this as I think it would benefit both of us and still fulfil your wants, I do respect the journey and hope you buy mine but wish you the best