Oppinion is needed about EXHAUST system! Thanks - The Unofficial BMW M5 Messageboard (m5board.com)

First e28 M5 · 15th March 2009, 10:57

Hi M5 friends,
I have E30 M3 with S38-B36 and I still have the 4cyl Exhaust on the car. I would like to upgrade to the ringht one.

I have heared the the best comination is 2.5 inch from the headers to the Cats and from the cats all the way back using 3.0 inch piping.

Now what is the best piping diameter numbers in order to have free flow and make the car as fast as possible. I dont care if I lose torque but gain hp ot how loud will be.

Do I lose Torque and gain HP ?

Please oppinion is needed.

Anri

inertia8 · 15th March 2009, 16:31

Do you care about noise levels? I would think that would be rather loud.

Generally on other cars, I've seen people use reducing diameter the further away they get from the headers... but I've seen nothing specific to S38..

I'm in a situation where I'll have to redo my exhaust as it simply goes from headers straight into 2.25" stainless press-bent, magnaflow cat, magnaflow 4" barrel, magnaflow 2x3" muffler at back.
It sounds great but I believe it to be more restrictive than stock... so will be looking closely at what responses you get here.

pspassos · 15th March 2009, 19:21

stock would be a little bit less than 2.25'' in eache pipe all the way.... if you put 2.5 or even 3 inches in both pipes it would be realising some "horses" in the low end, but low end torque would be compromissedmaking