AssassinJN

Ok I know this is a dumb question but I still want to know the answer and am ready with flame retardant clothes, so here goes.

Some exhausts (on the S I have heard it with the supersprint and I believe the hks) make a sound that I can only describe as "blum blum blum" when decelerating (may only be during breaking but wanted to make sure I cover all bases) that I have always enjoyed (my prelude made the same sound) as I thought it sounded racey (not ricey).

My question is what actually creates this sound? I assume it has to do with back pressure meeting with outgoing exhaust gasses causing a sort of pop when the built up pressure is released. But I am not sure if this is correct. Also does hearing this sound mean that the exhaust is too small (not enough out flow), too big (engine doesn't flow enough to keep the air moving allowing more back flow), or is it not related to this at all?

Also why doesn't the stock exhaust make this sound? When some after market exhaust that flow more than stock do make the sound (supersprint) but some higher flow exhausts do not. Could this mean that it has to do more with the muffler design?

Anyone have any insight, or even more speculations?

afwfjustin

Sounds like backfire. Are you running a test pipe? Get a tuning device and lean your a/f ratio.

Or, you could get an EMS and have the tuner cut spark before fuel and start shooting flames

Spec_Ops2087

Nah backfire is a loud pop or bang even. Some backfires can even sound as loud as a gunshot going off.

As far as what that noise is, I have no idea; havn't taken enough classes to really tell you. My guess is when your deaccelerating the TB is closed, making some negative pressure (since the cylinders are still going and they want to pull air in) so maybe the act of wanting to push the air out of the exhaust and the want to pull air in will create the turbalance that we know as "blumb blumb blumb"

Just speculating

Jay2000

All that extra horsepower coming from the supersprint.

PrimoGen

sounds like you are describing back pressure sounds

Aze85

when i had my invidia + tp on it made that noise when i decelerated in gear at high rpms. for instance, i floor it in third up to like 7000-8000rpm and then i let off the gas. i would let off the gas not immediately, but not very slowly either. it would make some crazy noises kinda like u described.

ej3ffrey

i get that same sound too with my invidia... i also had that sound when i had a greddy on my accord.