Hey guys. It's time for me to change the exhaust setup in my car. I was hoping some of you have had some experience with N/A large port exhaust setups. I'm ordering a new header from Rotary-works and will be changing out my current dual 2" piping for some 2.25" pipe as well as removing the dual rear mufflers for one single muffler. I have been told that my primary pipes need to be 92" long form engine to converge point. It then would be a single 3.5" pipe over the axle into a muffler. I would also like to know if you guys would have a good suggestion on a muffler. Right now i have 2 magnaflow resinators and 2 eldlebrock mufflers.

 

my plan for system 2.1 is this;

the RB header, collector and borla get reused. i'm gong to buy a pair of 4' long pipes, and clamp it together, and go to the dyno, and cut it until the engine is happy.

I would like a long system too, but actually i'm going to let the engine decide what it wants, and actually the shorter the more room i'll have for mufflers....

stage 2.2 is mufflers that muffle, the borla is a POS. ideally in a 1st gen i want an 8" round, by 20" long muffler, that's about the biggest that will fit, however FINDING that is expensive (MFR lavarock for $500) or requires a trip to japan, or you can roll your own....

 

Try coast fabrication. http://www.coastfab.com/ They can make lava rock mufflers that will stand up to a peripheral port.

 

I would just rock the rb streetport system. Otherwise, pm Blown7 as he has been running a peripheral port in his fb for years now.

On a side note, a local builder experimented a lot with his peri-port fc. restricting the exhaust kills huge power! His resolution for a street/race comprise was simple, removable silencers at the tips of his dual exhaust (I think they were borlas, not sure though). I believe removing the tips freed something like 30 hp....but loud and proud as a peripheral needs to be though.

 

Dont go 2.25" primary pipe. Its way to large. And you cant just build a exhaust to 92", there are soooo many factors that will determine the ideal length.

 

I'm such an idiot, lol,.....pm blown7...... he "started" the thread

 

Why is 2.25 too large? Im not even sure I understand how exhaust can be too large. Not being sarcastic or arguementative in anyway, I just sincerely dont understand how too large could hurt anything. Also take into consideration that my point of reference comes from drag racing and not caring about street manners or driveability, just max power for 1/4 mile.
If Im gonna pump extra exhaust gases out the pipe from nitrous, is 2.25 still too big? My logic was that a bigger pipe is better cuz I need to make room for all those gasses to get out to have the freshest charge on the next cycle. I dont understand header length and collectors either, since when V8 cars get to certain power levels they dont even collect em anymore and just run zoomies.
And 10 years ago everyone thought 3 inch on a turbo car was huge, now people run 5 inch. Seems like, as long as you had zero back pressure you would be good to go. Im not some engineer, thats why Im throwing my thoughts out there.

 

If the pipe is too large, the exhaust gases have to be pushed out because they lose inertia.

A good exhaust will have a vacuum in the pipe near the end of the exhaust cycle because of the slug of gases pulling the exhaust out. If the exhaust is too large, then this effect is lost, and power drops.

So yes, it IS a backpressure issue... pipes that are too large will create backpressure.

 

Mine is 94" long but as said many things come into play and have an effect on length. 2" primaries and 3" rear section.

https://www.rx7club.com/naturally-aspirated-performance-forum-220/fc-egi-project-813134/page4/