Car makes gasping noise when shutting off (under hood)

[90gs]

ok ive been trying to take my catalytic convertor off for a while but never had anything but a POS socket wrench, so today i went out and bought a breaker bar.

i jacked up the car and took off both front tires so i could access the bolts i needed to take off. i sprayed WD-40 all over the bolts and let it sit for a few minutes then went to work, i snapped off the first bolt with minor effort (cranked on breaker bar and the bolt snapped) and then i realized that i'd need new bolts after putting in the test pipe. so i decided to wait until i got new bolts before i took off the rest of the bolts so right now theres the 3 bolts connecting the cat-back to the cat and 1 bolt connecting the cat to the downpipe (remember 1 bolt is broken) now my car makes a rather large gasping noise when i shut it off. that is air rushing into the header right? is that a bad thing? as long as i dont shut off the car while the revs are dropping i wont crack the head will i?

[sameintheend01]

Originally posted by 90gs
ok ive been trying to take my catalytic convertor off for a while but never had anything but a POS socket wrench, so today i went out and bought a breaker bar.

i jacked up the car and took off both front tires so i could access the bolts i needed to take off. i sprayed WD-40 all over the bolts and let it sit for a few minutes then went to work, i snapped off the first bolt with minor effort (cranked on breaker bar and the bolt snapped) and then i realized that i'd need new bolts after putting in the test pipe. so i decided to wait until i got new bolts before i took off the rest of the bolts so right now theres the 3 bolts connecting the cat-back to the cat and 1 bolt connecting the cat to the downpipe (remember 1 bolt is broken) now my car makes a rather large gasping noise when i shut it off. that is air rushing into the header right? is that a bad thing? as long as i dont shut off the car while the revs are dropping i wont crack the head will i?

why do you need need bolts with the test pipe? if you are so worried, just take the cat off for a couple days. i don't think you could crack the head from air pressure left in the exhaust system.

[91civicDXdude]

I think he means he has an exhaust leak now. It shouldn't really hurt anything besides sound crappy. Hurry and get it fixed though.

[90gs]

yea ima buy some new bolts and get that sealed up and once i have the money ill buy a bomz high flow cat and put that on there in place of the stock cat..

[GSR]

leave the cat on there until you have a replacement. if you leave it open header you run the risk of bending a valve

[90gs]

i wont risk bending a valve if i have a test pipe though right? im deciding between BOMZ high flow cat and a test pipe. i hear that the BOMZ high flow cat is just a resonated test pipe and resonation makes it sound deeper.. i dont like ricey sound so im thinking ill do that

[ProShift]

I dont think it has much to do with your exhaust, I would check your pcv valve

[ZedEx]

It's just the engine turning down. Do you have an intake? Have your friend shut the car off, while you're standing in front of the car with the hood open. Listen to your intake, I guarantee you that's where the noise is coming from.

Both my Type-R and Prelude do this.

[Twizted_3KGT]

Sounds like it's just your intake to me. My Integra did this, my buddies Accord does it, and pretty much every car with a cold air intake i've seen does it. You won't be bending valves from having an open header. AFAIK that's just an urban myth involving cold air entering through the header and warping the hot valve...highly highly highly unlikely.

[ZedEx]

^ Pretty much.

Not even necessarily a cold air intake, even an open throttle body will do it. Just any aftermarket intake in general, I think even the Comptech Icebox does it.

Running open header will not damage anything.

[Ascendance]

That's the first thing I thought too, my intake does this.