I went to a friend of mine yesterday, whose occupation is to build high performance exhaust system, obviously to have a custom exhaust on my FD.
We looked at the stock exhaust and measured the pipe diameter.
Well it's not so easy to define it and in fact varies from 60 to 65 mm.
I told him that i wanted an alltheway 76mm exhast (more or less 3") because I always saw them to be this measure in the shops around USA.
He told me two things:
1) he can't bend 76mm, his CNC mandrel bender takes up to 65mm
2) he never saw a diameter such big apart from Ferrari Enzo (80mm) and Lamborghini marine engines (90/100mm+water jacket) all the other use 63.5mm (2.5") even Delta Evo, Mitsu Evo, M3 and so on.
Now, my question is: is there any particular reason for the pipe to be 3"?
Is this a specific need of the littlehearted-bigpower FD Wankel?
Has any of you ever saw/used/tried 2.5" exhaust system on FD?
I can think of no reason to use big diameter exhaust (over 65mm), well i know that talking about turbocharged engines the bigger the better, but i can't think of why only the FD has to use 3" pipes.
Delta Evo and Mitsu Evo are Turbocharged and comparable in power and revs, but they use a smaller pipe even when racing.
Any suggestion?

 

i had a 2.5 in. cat back on my car for a while.....as i replaced the other segments of my exhaust(downpipe then midpipe), i saw marginal gains...but when i replaced the 2.5 inch piping at the cat back with 3inch piping i could not believe the difference....it was incredible....i would never use 2.5 inch piping again on a fd....the turbos spool faster and harder...and it gets alot louder.....2.5 inch piping definately hinders the aspiration of these little mills.....no doubt!!

 

3" pipe offers better exaust and heat flow away from the turbo's. The bigger diameter pipe allows for less restrictions and thus more horsepower. If you want real power increase from your FD either find a shop that can bend 3" pipe or just start buying the prebent sections like the rest of us.

 

3" is pretty much the standard for all turbo applications (in my experience) - I'd be looking for another "specialist"

 

Are these downpipe/midpipe on Ebay a good deal?
the price is quiete low (both for 199)

 

ive heard of fitment issues.... but for 199 you cant really go wrong

 

The midpipe doesn't fit too well, but it does bolt up. Mine rubbed on the floor of the car.

 

More flow more go... i think that would be the best way to explain it. along with the heat transfer away from the turbo's. Is your friend there just not have the inserts for his machine to bend the pipe? id look around at a few more places, i would think most shops would have the ability to bend that size pipe.