E30 Exhaust

[MR325es]

I have an '86 325es and am considering finding a used 325i exhaust and then to take out the cats and resonators(or whatever is in there, haven't seen one before) and weld in straight pipes so I would have straight pipes to a muffler of some sort. Who's done this before, or if you haven't is there a better performance option that i'm overlooking??? Oh, also will a 325i exhaust bolt up to my 325es manifold or will I need to pick up a used 325i manifold as well??? Thanks a lot. The main reason of doing this is that i want dual exhaust running back to reduce the pressure. Give me some feedback on what's best for more performance. And I don't care about sound, I'll have a muffler on the back.
-Marc

[MR 325]

Sounds like a great plan but you do need the 325i manifolds aswell. I'm not positive on the "e" ones bolting up or not but they are much more restrictive and the 325i exhaust would do much better with the matching manifolds.

[NoName]

The 325i exhaust will bolt up to the Eta manfilds no prob.

Exhaust ports on both engins are the same exact size so the monifolds are the same, except the runners on the Eta's have a slight curve, and the 2.5's are stright.

Top: ETA
Bottem: 2.5



I don't know if he minds me quoteing him so I'll leave his name out but most of you guys have heard of him.

when I dynoed my car when it was a 325e, it put out 115 RWHP with the Jim C chip and exhaust. A friend of mine in Florida with the same car, same mileage (at the time), and same mods (except the exhaust) put out 109 RWHP on the same type of dyno, so I'm gonna assume that you'll get a 5-6 HP gain.

[EThirD]

If you're going to cut and weld everything into straight pipes anyway, why not just go to an exhaust shop and get one custom bent? Also, the general consensus is that a 2.5 inch single pipe all the way back is a great way to go for the M20, so that's something to consider.

[hotghias]

since we're comparing 2 different cars, and there are so many variables, you can't really draw any definite conclusions about performance gains. i think 5-6 is a little generous based on what i've read, but who knows, i haven't done it.

if you do do it, do the environment a favor and weld in a high perf. universal cat. they flow pretty well.

[MR325es]

HAHA, well my step-dad and myself are kind of our own custom shop. He owns an automotive shop so I have access to most everything. Looks like i'll have to pick up the 325i manifold for extra flow and proper fit. Do you know where I can pick up high-flow cats for the 325i exhaust (looks like I'll need 2)?????? BTW, the engine has already been bored w/ new sleeves put in, new piston, all new oversized valves w/ a port job on the head, and the whole engine essentially blueprinted. I will be ordering the chip for it sometime this week as well.

[DSchultz325e]

one cat one silencer? i remember reading that you don't need the exhaust manifolds, you need the 2.5 intake manifold, otherwise the upgrade is worthless.

[MR325es]

I guess we'll try to figure something out, I don't want to go overboard on things by any means. People with eta's, let me hear what you guys have as far as exhaust setups go.

[e30josh]

i was thinkin of straight piping my car but i was told for a local enthusiast that i would lose torque due to not enough backpressure but gain some hp....id rather have more torque....