custom exhaust - rule of thumb tubing size - STU MC?

[george graves]

so in general what size ehaust should a 2.5 motor have?

How bout a 3.0?

What about, say a 3.5?

Assuming N/A motor, and street revs - is there a rule of thumb for exhaust size vs. engine displacement?

I'm thinking of 3" or 2.5 for my m30 swap.

George Graves

[Rob]

stu has 2.5", and alex has 3" AFAIK, so for an m30, i'd go either 2.75" or 3", but thats just me.

as for a rule of thumb, well you dont want too much diameter, but you dont want too little either. how about that for vague :P

[Mystikal]

I recall reading once that a standard rule is 2.5" for 2.0-3.0L, and 3.0" for 3.1L+. NA engines of course.

[latinobimmer]

Most guys on Mye28.com run a 3" on their 535's, if that is any help. I think 3" on a 325i would be a bit much, correct me if I'm wrong.

[e30Matt]

I'd run 2.5" with a few kinks and an X in it to keep backpressure.

[george graves]

I'd run 2.5" with a few kinks and an X in it to keep backpressure.

ummmm...

[Bavarian3]

On my ETA 2.5" and the M3s 3"...

[Rob]

I'd run 2.5" with a few kinks and an X in it to keep backpressure.

how does one put an X in a single pipe? sharpie?


if he goes 2.5", he'd want a very free flowing exhaust, since the diameter is 'small'

[M3 Ryan]

I need to know this too for my Euro Motor... I got a Borla XR-1 Race muffler to put on, that is 2.5" in and out, but can easily be made bigger (the inlet/outlet are pinched down from 3" to make it 2.5")...
I was thinking of doing 2.5" mandrel bent with a hi-flow car and a resonator, but I don't want it to be very loud...

[Rob]

if you run a cat, a resonator, and a muffler, it wont be too loud i dont think

[e30Matt]

I'd run 2.5" with a few kinks and an X in it to keep backpressure.

Wow... I'm a retard. :shock:

Totally had something else on the brain.

Maybe 2.5" w/a high flow cat, resonator, and a Brullen to make it sound nice?

[SlammedE30]

I'm running a 3" on my 3L. Seems to work fine.
-Ted

[e30evolution]

apart from scraping everywhere

last time i checked my car had two exhaust manifolds, and two pipe throught the cat, center muffler and muffler.... me thinks it wouldnt be hard to make an x-pipe..... but why?

[e30Matt]

apart from scraping everywhere

last time i checked my car had two exhaust manifolds, and two pipe throught the cat, center muffler and muffler.... me thinks it wouldnt be hard to make an x-pipe..... but why?

Backpressure.

[Mystikal]

Backpressure = bad thing.

And if one person says "but that's how torque is maintained!" I'll bitch slap them.