Loud exhaust ... need help!

[DennyG]

:wtf: Well ... I bought this 1993 Mustang GT ... added Edelbrock Performer heads, intake and 70mm throttle body, E303 cam (yeah, I know: big deal ...), roller rockers, .373 gears, a MAC off-road H-pipe and Maremont mufflers. The car ran real well but, with the stock exhaust system removed there is a very loud resonance between 1600 and 2200 RPM. It's so loud inside the car that you can't hear the stereo or have a conversation with a passenger. I was told that the resonance was the result of removing the stock exhaust but, if would put cats on it, the resonance would go away ....

Soooo ... when I added the Kenne Bell blower, 90mm MAF and SwitchChip I also added a 2.5" BBK H-pipe with high flow cats and Dynomax SuperTurbo mufflers ... the SuperTurbos do a great job of giving me just enough exhaust sound to remind me I'm driving a kick-ass car ... but the resonance is still there! ... so much for adding cats to solve the problem.

Now Dynomax is suggesting adding Bullet mufflers, as resonators, between the cats and the SuperTurbos ... which I'm willing to do if it'll work ... any wisdom with respect to the 5.0L exhaust resonance? I'd love to hear from some of you on this ... it's the one and only complaint I have about this, other wise, awesome car!

Thanks,
Denny

[bones]

You will always have some resonance with aftermarket mufflers and the RPM range you mention is exactly where it occurs. The off road H pipe is probably contributing a lot more than you think. I recommend you talk to Flowmaster. I have the original 2 chambers on my 92 LX and the new 2 chamber Delta Flows on my 03 Cobra and the difference in the resonance is very noticable while still keeping the muscle car sound.

[bones]

Sorry, I didn't notice you went with a catted H.

[DennyG]

bones ... thanks for the reply (doesn't seem to be much interest in communication around here ...) The catted H may have lessened the noise some ... but not much.

The stock setup is TOO quiet ... making me wonder if the exhaust noise was part of the reason behind two chambers on each bank in addition to the mufflers. I was thinking about switching it back to stock (I still have all the parts) but that seems counter-productive given all the money already spent to improve airflow.

One thing that seems strange is that the car, when started cold, doesn't exhibit the resonance, even when pushed pretty hard ... but as the car warms up the resonance gets louder ... exhaust leak? I haven't found one yet but who knows?

Thanks again,
Denny