Hi all,

I'm visiting from the E36 section of the forum. I've tried searching but can't find detailed information on what it is about the S54 engine that gives it its unique rasp/rattle when it is being pushed.

Can anyone give me a clear, definitive, technical explanation?

For the most part, it is characteristic of the S54 engine itself. But the exhaust configuration (particularly on US models) seems to amplify it at certain rpms (mostly in the lower midrange).
In the US version, there is one resonator in the Section 1 midpipe. There are two in Section 2. These help reduce rasp, but not completely. There are aftermarket S1 and S2 pipes with better resonators that drastically reduce the rasp, but the European configuration seems to be most effective.
In the Euro version, the catalytic converters are actually in S1 rather than in the headers as in the US version. They moved the cats from S1 to the headers for the US in order to reduce cold start emissions. This moved a resonant chamber (the cats) even closer to the source of the rasp.

Some love it, some hate it. One thing is for sure - there is no mistaking the sound when you hear it!

the rasp is due in part to the design of the headers, with the cats built into them. There was also some source that stated that the S1 pipes just after the cats would rattle at certain RPM's which greatly amplified the raspy tone. And in the end, its the muffler that really gives it that tin sound. I have replaced my headers and completely removed the cats, and with the stock piping and stock muffler, the sound is much louder, but still just as raspy. I am tempted to see what happens when i remove the muffler.

So I have replaced the headers, which has taken away some of the rasp. And we will see what happens to the exhaust note when I remove the muffler.

Many people have also found that using an X-pipe really removes most of the rasp. I would say that most of the rasp is coming from the midpipes and muffler.

As far as the motor's characteristics... it does tend to be a raspy motor, but there are plenty of exhaust setups that will completely change the tone to a point where there is no rasp what so ever. I personally like the stock exhaust note, and with my exhaust, i would like to keep some rasp. There are people who have setups where the rasp is completely gone; you would never know it was an M3 by the exhaust, a few even have a pretty deep growl to them.

At first that is what i wanted, but as time went on, I realized that I do want a high pitched scream. Its different than most tuner car exhaust notes.

+1, the US version is worse rasp wise...

I put one of the Rasp Terminators from Custom Performance Innovations on my M3 and it was well worth it. I didn't like the raspy sound. The car sounds great now. No raspy, tinny sound at all. It is an easy bolt on. I put mine on in the driveway.

www.custom-performance.net

I have completely different exhaust and I have more rasp and it sounds more aggressive. It has nothing to do with the exhaust it all comes from the motor.

I was hoping I could get some nice sound clips? :(

It has alot to due with the size of the combustion chamber and the piston speed in the chamber.

It has nothing to do with the exhaust it all comes from the motor.

Yep.

The rasp is indeed the engine but the exhaust can either help mask it or accentuate it.

I have completely different exhaust and I have more rasp and it sounds more aggressive. It has nothing to do with the exhaust it all comes from the motor.

I had just installed my Rogue Engineering Rasp Pipe with the El Diablo muffler...I have no rasp....I repeat no rasp, just a deep throaty tone and discreet until I STEP on it. :redspot

Oh yeah...I would highly recommend this set-up. Only if you want to wait for three months for the El Diablo :(