Question about Exhaust set up

[azian6er]

Hey, I had a quick question for everyone. Some people are running 3 inches all the way back. (crushed or mandrel?) I have a 2.5 inch DP on right now and am thinking about a custom 3inch cat back or 2.5 inch cat back. Would a 3ich cat back with a 2,5 inch downpipe be bad since i am changing diameters? Or would a 2.5 inch crush bent exhaust fit better with the 2.5 inch DP? . Oh and since my addition of my FMIC i am running super rich and stumbling like crazy. After i put my injen on and ran joes FPR kit it was good, but now it is stumbling like crazy. Any ideas/ suggestions? Would an AFC do the trick for now (not apexi one knob, one of the older 5 knob ones...)
Thanks again --Bryan

 

[MazdaspeedZOOM]

You know I've beein kinda wondering a similar thing, what's better to go with, a 3" exhaust or a 2.5", I've heard people say that you'll lose a lot of torque with the 3" and I've heard people say that 2.5" isn't enough, so whats the correct way to go, straight back from the turbo?

As for your question when changing diameter pipeing as long as you increase size ie 2.5 to 3 it's ok, just don't go in reverse, 2.5 to 2.25, I don't know if that makes sense or not, but it's just what I've always been told.

 

[Striker187]

you'll be fine going from a 2.5" dp to a 3" catback. that's my plan. just so long as you don't go back to a smaller size, cause think about it. you're creating a bottleneck which pretty much ruins the idea of what you were trying to accomplish in the first place. also, stay away from crush bends. it'll slow the exhaust gases down. i'm not sure which is better, 2.5" or 3", but here's what i've learned and you can make your decision.

2.5" should hold up to about 300 hp. i dunno how many of us will make that much hp without some serious mods. but then again, the evo VII in japan makes something like 300+ hp stock at it only uses 45mm piping...that's 1.7"!!!

3" piping will definitely be enough for you. most of the higher end cars use this (supras, rx7s, skylines, etc). some people say it's overkill. but there are many different schools of thought on this. since we are dealing with turbos, most will say it's good to have the least amount of backpressure so the larger the piping, the better. for na, it's good to have a little backpressure which is why they're designed to use smaller piping. my friend drives a turbo civic...he used to have a tanabe 2.5" exhaust, then he switched out to a 3" and there was a definite power gain. but some people say it's still overkill. so i guess it comes down to money, cause 3" piping will cost more than 2.5"....especially the mandrel bends. i'm still planning to go 3" cause the way i figure, if i do end up modding my car a lot, at least i'll have the exhaust system already in place so i don't have to buy another one.

there's my 2 cents

 

[iON Performance]

MazdaspeedZOOM - ideally for a turbo car, you want to maximize the pressure differential pre & post turbo. Hence using a 3" turbo-back will achieve this. The larger the differential, the faster the spool-up.

Striker187 - actually the EVO 7 isn't designed for max hp. It's a homologated rally car, specifically designed for power in a certain range. All the TT/ & D1 Evo's sport a minimum of 3" piping.

 

[Striker187]

ion - true true, my only point was that the evo can make that much power with that little diameter of stock piping.

 

[YuYuRena]

Be careful about switching diameter of the pipe cuz that will make some unwanted resonance if the pipe length isn't matched up correctly to where you want the sweet spot on the powerband. The reason is basically gas dynamic called Helmholtz resonance, that is much like how an organ works. Just a warning cuz you might gain some power in the powerband but might lose some. Just a warning.

 

[DiscreetSpeed]

so what would be the recommended size to maintain say torque?
but be able to recieve the max power

 

[Kenetix]

I've got custom 2 3/4 inch. Need to post a pic, even though it's gonna look just like everything else.

 

[azian6er]

read below again

 

[azian6er]

read below

 

[azian6er]

so basically what people are saying is that going from a 2.5 inch downpipe to a 3inch crush bent (muffler shop) exhaust with a custom welded on muffler would not work as well as a 2.5 inch mandrel bend exhaust?

Is there really so much power lost in the crush bends that 3inches wouldnt suffice? Because i think like if it is 3inch crush bent, then at the smallest diameter spot in the exhaust will be like 2.75 inches at the least.

Anybody else??

--Bryan
PS does anyone know what kind of exhaust joe p is running? I know its 3 inch but is it mandrel bent? Something tells me it wasnt oh well...

 

[Bigg Tim]

I think the 3" cruch bnd will be good enough. You are right, at the skinniest part it MAY go all the way down to 2.75", but that's got to be a hell of a bend. I don't think you will feel the difference in a 1/4 of an inch and it will cost a hell of a lot less than going with mandrel bent. Some guy told me something like $350 to make a 2" cat back out of mandrel bends and that's not including installation. I had it done for 60 bucks at a muffler shop. I'm getting perfworks' 3" with my turbo, it looks good and the bends are not crushed that much. It almost looks like mandrel bent pipes.