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      05-28-2013, 12:42 PM   #1
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Exhaust system theory classroom!

Hello,

I thought we could make this a exhaust system classroom, where you could post and discuss different theories around certain setups and what causality there is to be expected.

Perhaps, we could start off by discussing my setup, and its different characteristics;

I run the Eisenmann Race full setup, combined with flash tune and CAI.

Observations;

1. When cold starting, running idle creates a raspy sound, however, when driving cold, the sound is not very raspy. Exception is when engine braking if running cold, that creates quite loud blasts from what I assume is back pressure. This blast disappear quite quickly (after about 100 meters of driving) and turns into more deep and puffs.

2. If running the car to crusing temps, and then parking it so the exhaust turns cold, but not the engine, that creates a really raspy sound at first in high revs (directly after), until the exhaust turns warm again. Reminds me of a straight pipe GT3 RS. However, since the engine is warm, the idle has a deeper tone to it, but when given small throttle pushes, the sound is very raspy.

3. The warmer the whole package become, the less raspy sounds it creates.

4. When driving on a relatively high gear, and flooring it, the exhaust completely screams when reaching about 3K revs, no matter the gear and speed. (This is quite satisfying when driving in tunnels). However, driving on a relatively low gear, with higher revs, creates much less scream from the exhaust.

Im quite confused. Is there anyone in here with a sence of how an exhaust system really works, soundwise? Why does the tone change so much depending on speed, gear, temps and so on?

Thanks
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      05-28-2013, 02:38 PM   #2
Artemis
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Partially off topic: introduction to the basics of exhaust technology:
http://www.epi-eng.com/piston_engine...technology.htm
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      05-31-2013, 11:25 PM   #3
Eyeman
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Sounds like your exhaust works great but I'm sure it would be too loud for me. The worst thing I hate with my exhaust is when I get into it from a low RPM, I'll get a weird overload, vibration thing. My exhaust is listed below, catless dp but still using the stock midpipe.

For sure some of your tone issues are the wastegates. I had this one regular commute that I'd make where I typically drove a little faster than normal. Many times I got off the highway exit and came to my first stoplight and my exhaust would sort of startle me idling so much louder than normal. Within a minute or less it would drop back to normal. The wastegates make a big difference.
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      06-02-2013, 05:14 PM   #4
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Interesting

Quote:
Originally Posted by Eyeman View Post
Sounds like your exhaust works great but I'm sure it would be too loud for me. The worst thing I hate with my exhaust is when I get into it from a low RPM, I'll get a weird overload, vibration thing. My exhaust is listed below, catless dp but still using the stock midpipe.

For sure some of your tone issues are the wastegates. I had this one regular commute that I'd make where I typically drove a little faster than normal. Many times I got off the highway exit and came to my first stoplight and my exhaust would sort of startle me idling so much louder than normal. Within a minute or less it would drop back to normal. The wastegates make a big difference.
Would really like to elaborate on the wastegate thing.
Gonna go study turbo tech now.
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