Exhaust diameter...

[valvesprung]

Alright I did some searching and couldn't find what I was looking for...

The car: '91 318i

I have access to a large amount of mandrel bent 2.5" exhaust tubing and a few really nice resonators (100mi old off of a Mazda Speed3), as well as a 2.5" cat. Will this combo be too obnoxious for an around town daily driver? The cost will be quite low and I'm a big advocate of a good sexy exhasut note.

What have you guys found from personal experience?

[Cristian G in Oz]

I would go with 2.5 to the cat and then 2 the rest of the way.

A hotdog up front and a proper muffler down the back should do it nicely, with the 2.5 cat in the middle.

Be aware that cats are consumables and if it has done more than about 1000kms your better off getting a new one. Spend the money here and get a ceramic high flow/race jobby (depending on your polution rules of course).

This is what I am going to do when my current exhaust falls off. This same system worked for my suby and my E12 3.5ltr (I had 2 hotdogs in this).

Let us know how it turns out.

Cristian

[valvesprung]

Thanks for the input, but 2" is smaller than the OE tubing...that won't gain any thing in the power dept...

[denious]

Unfortunately, neither will 3"

[valvesprung]

Obviously I'm well aware that too large will have as many negative effects as too small, that's why I'm for some input on the best of both worlds.

[denious]

Hm... So if 2" is too small, and 3" is too large, I say BMW calculated everything and gave us a marvelous, non-restrictive, 2.5" exhaust tubing! :p

[valvesprung]

Stock isn't 2.5", but 2.25", which is why I ask...is 2.5" too large.

Here's a better question...who has 2.5" on an M42, how does it fell, sound, etc...

[denious]

Well I just got owned... I forgot that stock is 2.25"... I have 2.5" mandrel bent all the way, took the cat off and put a generic resonator 10$ and a cheap mufler (30$). The sound is... Overwhelming? But my system is cheap, so it depends on what you get... I DO think I could see a slight difference during acceleration, but it could just be a placebo effect 'cause in my head 2.5" should've made it better; I never dynoed the car.

[valvesprung]

Gotcha, thanks. I will be running a 2.5" cat, resonator, and rear muffler so I think I'll be in good shape based on what I've read around the forums.

[denious]

You wanna install a resonator AND a cat..?

Oh and don't forget to post sound clips!

[valvesprung]

I am a big advocate of great sounding exhaust, and the last thing I want is a ricey sounding exhaust...and as stated I have the parts.

[xsjado]

if im running a catless setup, the should i b running a 2.5 to the hotdog then 2 till the muffler??is that right??

[eric ^__^]

is there really all that much power to be had by massaging the m42's stock exhaust system?

Who's got the supersprint setup installed?

[gearheadE30]

The exhaust system is fine except for the muffler. Factory headers and decently large piping with few bends makes for a really good stock exhaust compared to many "modern" cars . A free-flow muffler will only get maybe 1-2 hp out of it, though.

[eric ^__^]

that's what I thought