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Discussion Starter · #1 ·
I got a 04 r6 and recently noticed when I rev it in neutral with my hand at the exhaust tip, it blows out while its being revved but while the revs are dropping i can feel it sucking in air pretty strong. Is this normal? Never heard of this happening before it makes me think it might need a valve adjustment or something but wanna know if this is normal or not before I get to tearing it apart. Thanks
 

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Not an answer to your question, but it might be why they tell you to stay steady (don't let up) on the accelerator when traveling through high water.

<<.......... If you were to remove your foot from the throttle pedal not only would water be “allowed in”, the resulting vacuum in the pipe would actually suck it in. So the rule is never, ever….ever take your foot off the gas when driving through flood water. ............>>

...yip, turns out that does answer your question. That is interesting.
 

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Discussion Starter · #3 ·
Not an answer to your question, but it might be why they tell you to stay steady (don't let up) on the accelerator when traveling through high water.

<<.......... If you were to remove your foot from the throttle pedal not only would water be “allowed in”, the resulting vacuum in the pipe would actually suck it in. So the rule is never, ever….ever take your foot off the gas when driving through flood water. ............>>

...yip, turns out that does answer your question. That is interesting.
That makes sense, when i think about it deeper it makes a little more sense to me because when the throttle is closed and the rpms are still high there is not as much air moving through the intake since the butterfly valves are closed, which ends up creating a negative pressure in the exhaust since there is not enough air coming into the cylinder to match the rpms, then it goes back to normal once it drops down to idle? Idk just a guess but it makes sense to me im bad at explaining things
 

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What's interesting is, there's still output; just not as much output. It's only "suction" from the standpoint of being at the end of the tailpipe... and because there's still output, that "suction" effect should be brief. If it were somehow possible to dynamically shorten the exhaust, there would be no "suction".

As for this stalling the engine, I think it's the fact that the engine is attempting to move a dense heavy liquid, out of the exhaust using only air that is the problem. Add to that, the momentum of that liquid rushing in, combined with trying to push it back out through the many tiny holes and passages of the muffler. It just overwhelms the engine with too much backpressure.

It occurs to me that this may be how "engine braking" works; though with air instead of water. (bigrigs may enhance by repeatedly capping exhaust or by adjusting valve-timing)
 

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The jake brake pipes exhaust back to the intake making a fixed volume of air move in a loop preventing rev increase since no more volume can occur.
 
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