Bimmer32

Check this link out:

http://nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm

It has some information on the principles of exhaust system if anyone is thinking about changing out stock exhaust system.

MiamiPhill

That was some good stuff....I always love those (....world is not flat) moments in life.

jet190rs

good stuff

Bimmer32

Here's another one that is more scientific and engineered based.

http://nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm

Based on the article above, it appears that reactive mufflers(tubes and chambers) are most effective silencers but not necessary maintain pressure (they make good back pressure). Reactive mufflers also are good for low frequencies cancellation (e.g., droning). Factory mufflers used a combination reactive/absorption technique. Following the reactive muffler, you should have an absorptive silencer (perforated straight through pipes with fiberglass shielding, e.g. cherry bombs, and then a short tail pipe.

OK, now to the BMW V8 exhaust system. It appears that they have 2 small resonators (low frequency silencers, but only effective at certain engine load), follow by a box resonator (perhaps a reactive muffler - I do not know for sure, but if I knock on it and sounds solid, it's absorptive (glass pack), if it's hollow sounding, then it's a reactive silencer (tubes and chamber), follow by a long pipe to a reactive/absorption muffler and branching to a second (not secondary) reactive/absorption muffler to be used depending on engine load.

Did everybody followed that? Hence, the stock exhaust is quiet (low frequencies cancelled by resonators) at low engine load (low rpm) but a louder sound (still tamed) at higher engine load (higher rpm). There's some real serious engineering in these exhaust.

When we go aftermarket exhaust, the systems or parts that specify for particular make and model engine have been tested to produce x pressure, x frequencies, and x engine load. I wish exhaust company would be more technical on these specs. When we go with "universal" parts, despite the name brand," it's simply a "TRIAL AND ERROR." There's no real specific or quantifiable answer because such parts have not be tested, recorded, or documented. That's just too bad.

s4iscool

you give most exhaust "tuners" too much credit. VERY few actually dyno tune them in development, most are simply generic mufflers that they design to fit into the right space, and call it a day. This is why you see a lot of exhausts that utlimately HURT performance but make extra noise.

westcoast550

Great article ,

Thanks

Audi_Eatter

Great info.
Thanks for the clicky.

Bimmer32

You're pretty much right on. I'm learning it the hard way. Systems like RDsport, while they are expensive, are designed and test for, say, the M5 or 5 series, which is still better than "universal" parts. Yet, even the more expensive systems don't have technical data like db levels vs. engine loads, hp and torque gains (RDsport only has dyno charts).

Most of the time, free flow designs don't hurt performance parse, but the extra noise is definitely there. True exhaust tuners should have dynos and db meter to properly tune an exhaust system. They're excuse is that there are too many engines out there to provide technical data. BS. They're providing low cost for the mass, but not necessarily low quality. Companies like Renntech and RDSport are more focused. I guess you get what you pay for.

Bimmer32

I meant to give you this link, which tackles exhaust noise from an engineering perspective:

http://www.enoisecontrol.com/related_artic...arrier_wall.pdf

Though it is about generator exhaust noise control, every bit of it applies to auto exhaust noise. If you're planning to change out your exhaust system or piece meal your own with universal parts, read this presentation to get a better understanding and how you may be able to achieve the exhaust note and sound level you desire.