dual exhaust for an m42?

[Rally Culture]

im looking at exhausts and im debating weather to have one custom made or buy one off the shelf. i see that most people just run a single pipe but since the headers split it in to 2 i thought it wud be cool to keep it dual. is anyone here running a dual set up that might have a video sound clip of it? how does it sound? im sure there is no real advantage stock but adding power down the road may change that. i was thinking if i go custom to have the set up come out the driver side just in front of the rear wheel. what kind of set ups are people on here running? pix and info wud be great thanks.

[Darky]

My engine came with dual exhaust system. Dual 1.5 from memory. Was very very loud though.
It worked quite well too, however the disadvantage of a complete dual system is that it can cause uneven flow between the cylinders. Which can cause problems with the engine.

The e30 m3 had a dual exhaust for clearance to ground reasons, but it also had x pieces in the system to negate that problem!
Cheers Rohan

[Warsteiner]

Hey...I'm all for doing cool stuff! Just make sure that it works for your set up.
My thoughts on making exhausts larger without making any other changes to the motor leads to not enough back pressure and loss of performance. Just adding a muffler changes the tone and overall sound but I don't think that it adds performance without other changes. You could look at the entire system as a whole from the AFM or MAF to the muffler and find out where your restriction is before you change just one thing. A muffler isn't going to change much but it definitely sounds better. As for the side exhaust, you could actually turn it to exit on the passenger side instead because it can get loud and you're now limited on space because you just cut a bunch of space off from shortening the system to fit either the cat or resonator and muffler to baffle the sound.
I personally run MAP (manifold absolute pressure) from my ITB's with 6mm valves, ported head, slightly larger header and a complete 2 pipe E30M3 exhaust with a SuperSprint muffler. Its quiet and sounds good. No droning anywhere in the rev band. I also have a stroker motor that can produce the extra flow.

I say talk to someone about how your motor is set up and then make a decision from there. 

Just for informational purposes, the 2 pipe system is most often used for ground clearance and no other reason. You can easily run a single pipe and get the same performance depending on modifications.

Rohan is correct as well, the x-pipe in the M3 system has a lot to do with the flow and pressure. IF you remove that piece from the system then the car loses a ton of torque. It's been proven. Flow is very important but so is back pressure. And prior to the x-pipe there is another H-pipe in the header for flow and resonance as well where the O2 sensor is placed.

HTH....

Cheers,
~Ralph

[Rally Culture]

ok i was wondering why bmw wud from the factory do a dual setup on a I4, wasnt sure if it had to do with performance. the po hacked up a straight pipe with a crummy resonator and muffler which sounds like an angry loud lawn mower, not a very pleasant sound. i would like the ground clearance so ill go with the dual and be sure to have a x-pipe setup to keep from having problems thanks for the info. do either of u guys have links of where u got ur exhausts? my car will be stock for now till i can save enough money for a turbo project, in the distant future . i love the sound of f1 cars and sport bikes and i wish i cud get that sound with out making my ears bleed or having to build a race motor that ill never be able to afford but i can dream i guess haha.

[Darky]

Hi
Having a oversized exhaust is a bad thing, the car will run poorly until the upgraded engine is complete and installed. The exhaust manifold has to built to suit the exhaust cam the inlet manifold should be built to suit stroke and bore with the length determined by inlet camshaft. In short the whole setup should be done at once.

Turbos can never sound like much, other than a turbo, because the turbo acts like a resonator controlling the exhaust flow.

Cheers Rohan

[Warsteiner]

Rohan is absolutely correct and thats what I was going to say as well. If you have a stock motor now, then stick with a stock configuration for the exhaust as a single pipe. The original system doesn't hang down too far and you don't need a dual at the moment as it will make your car run horribly if too large. An E30M3 exhaust system is "unobtanium" at this point due to the value of the cars these days and if you do find one you need a custom transition pipe from the header to the x-pipe which takes a lot of skill, money and time! And that may not be the best for your future endeavor of you turbo set up.

Maybe some of the Turbo guys on here can chime in and give you some ideas on exhaust configurations that will work but again, I believe a single pipe and even if larger than stock should work just fine for clearance. I have a 3" Single pipe on my 2.5L M3 and its fine.

Cheers,
~Ralp