I have a 1990 Vert that I bought last year. I immediately needed some "rumble" to the sound so I installed a s/steel Magnaflow cat back. I was disappointed still in the sound. I then removed the main Cat and replaced it with a hi-flow Catco one and removed the 2 precats and sleeved the areas. Got the sound finally that I wanted but got the "dreaded drone".
I was at Midas the other day on a unrelated matter and noticed that they had 18" long x 4" dia. glasspacks. I was wondering if they were put into the area where the precats used to be if I could stop or minimize the drone sound.
Has anybody tried this type of application already? Opinions please.
thanks
Bill

 

try installing a squirrel cage. they are a lot quieter


I have a 57 t-bird, and the muffler shop installed two 12" glasspacks to cut the resonance.
I have a 57 chevy pickup with 4 foot glasspacks, and no resonance.
I think the key here is that there is no "Y" pipe where the exhaust from the right and left exhaust manifolds collide.
Removing the cats removed a device that transformed the sound wave, and slowed the power pulses.
Now you have lost both benefits and replaced them with a freer flowing exhaust.

The glasspacks have a mesh cage inside where the glass is held in check, and I think the exhaust note is subdued by all those little niches. You can try it. Don't expect your exhaust to pass smog inspection checks any time soon. Part of the visual inspection is to see that the "system" isn't altered.

You might be able to get 2 " glasspacks, but I think you have 2 1/2" pipes up front.

The pickup has a ZZ4 engine (a modern L98 for relevance) Summit Racing L-98 cam, 89 corvette exhaust manifolds, 4 foot glasspacks,
and a 88 corvette 4+3 trans and cruises 75 mph at 2000 RPM.
it's quiet as a new car at idle, nice tone around town, and doesn't drone or get really loud on the freeway.
The glasspacks have been on there so long, the glass is probably all burned out, and they act as an expansion chamber.

 

Thanks..looks like it can work. I have 2-1/4" from the exhaust manifold and can get that size. I just have to check now if the 4' dia. will interfere with the X brace. Emission wise; where I go they just check for the sniff test. I have dealt with them for many years and I should be okay.

 

I reduced the drone noticeably by covering the trunk floor with sound dampening material. Removed the carpets and used A/C duct foam/foil to cover the floor, sides, and back panels. Cost about $30.

 

Best cure for "droning"... put the stock mufflers back on

ALL aftermarket systems (with the possible exception of Corsa) are louder than stock, it's all in how much "drone" you want to tolerate

 

:Sigh: That's why I love my Corsas.

 

 

DRONE and LOUD exhaust get's old real fast.
OEM exhaust for me.

 

Do a search, I use SS plug in one of my exhaust pipes on each side, sounds wacky,, but it works and is reversible.

 

I did that on my 86 with some wadded up aluminum foil, big difference in the amount of drone. It didn't eliminate it, but reduced to almost nothing. Cost is minimal to try it. The drone is a resonance with several sound waves overlapping at just the right(wrong) time and plugging one of the 4 pipes disrupts that.

 

Another possible cure to the "drone" is welding another 2" section of pipe so your tips stick further out of the back. From what I've come to understand, the droning is caused by the exhaust noise reverberating on the underside of the car and, if the tips stick out behind the bumper far enough, the sound will not have enough space to bounce off and therefore reduce the drone consideribly.

Before I put the tips on my car, the pipe stuck out about 3.5-4" from the back, and I had NO drone, but it was also straight pipe from a single muffler. Now that I have 3.5" dual tips, they're only 2" out from the bumper and there is a slight amount of drone, but not as much as I'd expect coming from such big tips.

If you stand behind my car when idling, it sounds like I have the bass cranked up on my radio.

 

This didn't work with my car. I've had my tips stick out about two inches from the bumper and I've had them flush with the bumper. Either tip location had the same annoying resonance. Although this is with long tube headers, no cats, true duals with an x-pipe and Flowmaster 40s which will probably resonate regardless of what you do.

 

This extra pipe fix worked well on my '89: true dual exaust, no cats and borla ZR1 mufflers. It reduced the drone about ~75% from what it was.

 

Copla years ago I pulled the rear carpet and laid down some cheap poly underlayment in an attempt to stilfle the drone. It didn't work but, when the carpet was out, I determined that the drone was caused vibration of the floor and side panels in the rear hatch, especially from vibration in the well under the RR storage compartment. With the carpet out I could bring idle up to 1200rpm and lower the drone by pressing down on the bottom of that well only.

It seems that these panels need to be stiffened to stop this vibration. Some have done this by gluing down thick and (relatively) heavy padding which tends to dampen said vibration.

 

I have a Flowmaster Super 44, and it didn't resonate at that point at all. The difference is that it was at 4" out, and currently it is 2" with more resonance. I think after 3"+ it will make the difference.