C4 Exhaust Resonance Tips

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After battling with 3 different cat back systems, and 3
different front Y pipes on my mostly stock 1990 corvette coupe, I have
learned that the C4 corvettes can and often do have a exhaust resonance
(droan) problem.
After researching the matter and doing a lot of
switching, installing, and reinstalling system after system I have some
tips that I would like to share.
All tips here are solely trial
and error and have been either performed by myself or someone else on the
Also please note Iam not taking credit for any tip listed
here that was told to me from another forum member…..I am simply
combining my own with theirs to give a complete overview into solving a
resonance problem.
So without anymore credits and
acknoledgements….here are the tips!
1. Make sure that you have no
metal on metal contact in the exhaust system. As far as the hangers
contacting the mufflers and pipes….NOTE: the clamp that goes around the
Y Pipe is ok….and the clamp that holds the air tube to the exhaust is
also ok…
2. Double and triple check the rubber items in the
exhaust system…..the hanger strap on the rear Y pipe & the rubber
grommets that are sandwiched between the muffler hangers and the cars
3. Try adjusting the the height of the tailpipes or
mufflers from the bottom of the bumper….There seems to be a sound loop
that develops a standing wave under the back of the car and causes a nasty
resonance…..By moving the pipes lower…..it may help.
people have reported that sound barrier\’s….IE dynamat´┐Ż or sound
proofing material, may help…..note MAY help……this seems to vary from
vette to vette.
5. Rear Y-pipe with a cross-over tube most people
(including myself) say helps out the car.
6. Blocking off or
sealing one outlet to a multi-pipe muffler, will usually get rid of
resonace. BUT…note this is being done by adding more backpressure to the
Last but definitely not least….check, check, and double
check your entire system….from the clearance of the exhaust pipes to
your bumper……to the rubber gromments that are sandwiched between the
muffler hangers.
I hope this helps!
see you on the

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