Exhaust Questions M30 - need experienced opinions

[talltorontoguy]

Last year I finished my M30B35 conversion.

One thing I had to rush was the exhaust....

- E34 535 downpipes with custom 02 bung in downpipe
- factory E30 325 setup from end of downpipes, cat all the way to tailpipe

Now I'm second guessing. I wonder is this setup restrictive somehow? The E30 325 pipes are smaller than the E34 pipes (I don't know the diameters off hand).

Comments? Ideas?

[e30_kid89]

I'd say it's restrictive. Id say change it, But i think you're going Turbo? If not hold out then go with something bigger when you do that.

[yert315]

you are going from a 2.5l to a 3.5l. It's going to exhale much more exhaust. I would go a custom setup from the headers back. My guess would be that single 2.5-3" piping should suffice.

[talltorontoguy]

Turbo is definitely a consideration, but won't happen this season. So... I'm looking for something that works right, now.

Has anyone actually done the math on this? Anyone know the stock diameter of the 325 and the e34 535 exhausts? (I think that it's 50mm/2" dual)

This has some info about E28 setups... http://home.mindspring.com/~scrappycrow/e28exhaust.html

[pegase747]

I guess if you use a nice uprated ( more flow ) 325i system, it shouldnt be too restrictive.
Or you could use the table on the link you provided to get the informations on what tube size, diameter, and mufflers/cats you need to adapt a nice B35 Exhaust system to you E30.

It also depends on your preferences, if you want a loud or quiet car...

Not enough restriction may give you a different engine behaviour too i believe, like torque curve change and so on...

Compromising is the answer...and it depends on your tastes...

My choice would be to adapt an uprated E34 sytem ( stainless ) with magnaflow cats under the E30 chassis, using the E34 downpipes, and free flow mufflers. 2 little exits as on a standard 325, or slightly bigger.
I want to have a sleeper, but a nice metallic growl above 3-4000rpm would be nice !

Pierre