Exhaust System

[Jose Luis]

what can i do in my exhaust system to enhance performance but without generating much noise-:confused:

[ak96ss]

I'm very partial to my Triflo exhaust, but it is quite a bit more expensive than most people are willing to do on these cars.

[Cobra Jet]

Being a performance & Mustang Enthusiast, I will say this - the exhaust header (commonly referred to as the exhaust manifold by some) that comes from the factory on the M42 is REALLY an excellent and free flowing design for a factory issued part.  It's mandrel bent (very smooth curves), the exhaust openings and tubing are a very generous size (I think they are 1 5/8"), there is smooth transition into each header tube, it flows exactly like a performance header, there are hardly any restrictions even down to the collector and the part is made of SS, which again is excellent.

IMO, spending $$$ on some aftermarket exhaust header for an M42 is pointless and a total waste of $$$.  The factory part is of very high quality, is by far an excellent free flowing, low restriction design that offers the best performance.

If you are going to upgrade any part of the exhaust on an M42 - it would be after the exhaust header collector:

1) upgrade the mid pipe to a slightly larger diameter

2) upgrade the factory catalytic converter to a high-flow catalytic converter that would match the mid pipe's size increase

3) upgrade the catback pipe to a slightly larger diameter

4) upgrade the muffler to a larger diameter, but also one that is less restrictive



Exhaust is not just about "sound", it's about having a system that is not overly restrictive.

[tony92ic]

I would think that the 2.25" ID exhaust is more than sufficient for a 1.8l engine.  I'd go (or did go) with just a free flowing muffler. A free flow cat may be a good idea. I've never seen one of ours tested. Grassroots Motorsports just tested a handful on a Miata and the results were mixed. Even the best one wasn't good for more that a couple horsepower and at least one was worse. Interestingly a straight pipe was just marginally better than the best cat. Like 1/2 hp IIRC. Maybe somebody can find the article and correct any inaccuracies. I seem to have lost my copy.

My stock cat and Magnaflow muffler isn't a very loud setup but sounds nice and I assume flows better. I've never dynoed them so am not sure about the actual performance increase. Personally I have always felt that most BMW's have pretty good exhausts performance wise from the factory. There isn't big gains to be had here like there is with a Civic for example. This is assuming a lightly modified engine. If you've gone FI, or big cams, stroker, etc. That's a different story.

There were some very good threads on this topic about a year ago. Do a search. Some even had video/audio of the different systems.

[Hodge]

These men speak truth. M42 headers are indeed great exhaust manifolds and should probably be left alone.

I went with a high-flow Magnaflow Cat, 20" glasspack, and Magnaflow 14816 muffler. It is loud and raspy as hell, but it does what I need it to do, and it is also alot lighter and free flowing than the stock boxes.

[longms]

These men speak truth. M42 headers are indeed great exhaust manifolds and should probably be left alone.

I went with a high-flow Magnaflow Cat, 20" glasspack, and Magnaflow 14816 muffler. It is loud and raspy as hell, but it does what I need it to do, and it is also alot lighter and free flowing than the stock boxes.

Which cat did you go with from magnaflow?