[TCSGTO]

Originally Posted by Sirrotica

Upon doing a little searching on the internet about exhaust drone I found 2 things that people are praising to stop it. One of the things Pontiac did on the production line and I could never figure out why one muffler was longer than the other on dual exhaust Pontiacs and now I seem to have stumbled upon the answer.

5.0 Mustangs had the same set up with 2 different length mufflers. Those cars always sounded good until everybody started ripping out the cats and installing the loudest Flowmasters you could find.

[VAB5]

Thank you, everyone, for the great input.

So here's where I think I stand, and I'd like some opinions.

I have 2 Dynomax Super Turbo 17734 (14" shell, 18.5" overall, 2.5" inlet/outlet) with the Pypes X-Pipe system.

I'd like to swap one of the Super Turbo for one 17749 (20" shell, 25.5" overall length). These are the longer mufflers spec'd for the car (17734 and 17749 have the same shell diameter). I would then have a 14" and a 20" muffler on the car. Looks like stock was 14" and 17".

According to the thread thus far, the different lengths should break up the resonance. Can anyone see a downside to this setup? It seems to be the most straightforward approach, as everything is still clamped, not welded.

Much thanks!

[Sirrotica]

Probably the easiest approach to the problem, this should work from the information I've read. If it doesn't then of course there are other options to try, but if I were you this is how I'd approach the problem first. Please let us know if it solves the problem, as it will be of help for others with a drone problem from here on out. good luck with it, hope it solves your problem......................

[rexs73gto]

My original mufflers on my 73 GTO with a 400 auto were different size to but from what I remember they were a 17 inch & a 19 inch muffler & the shout one was on the right side. I don't know if it will make a differecne by haveing the short or long one on the right or left side. Now this is an added question to the mix about the muffler size on the right or left side. Will that make a difference??? SIRR if after you install & find out if the noise is gone PLEASE let us all know as this will be great news for all our pockets.

[Sirrotica]

It just seems that Pontiac engineers made the left one longer and I always thought it had something to do with the heat riser which was on the right side. Later on they did away with the heat riser so it had nothing to do with that. There should be no reason it won't work either way as the waves don't know right from left, just that the sides aren't a mirror image of each other.

If changing 1 muffler doesn't get rid of the drone completely I would defer to the ford theory of hanging weights on arms on one side of the exhaust secured to the pipes to change it further. I have no idea if these changes will work, but those are the steps I would take.

Then if I hadn't gotten the results I needed I would try either the J pipe, or the resonance chamber made to look like an H pipe in one of the other articles about resonating drone posted previously.

[shotgun]

I bought a car with Slowmasters on it a couple years back and could not stand the sound/drone.

About a year into driving it, daily driver, one of the mufflers started to leak, rusting out.

I needed to fix it quick to keepon the road so I checked my "stock" and replaced it with a used dynomax ST.

Drone etc. gone.

Actually sounded real good , looked funny, but sounded good having the mellow sound of the dynomax combined with crackle of the Slowmaster.

Often thought of using 2 different mufflers with the same case design (for esthetics ) since then.

May try it on my project.

[VAB5]

Update:

Installed the longer, 20" muffler on the driver's side, and left the 14" on the passenger side. Both are the Dynomax Super Turbo.

Result? No change in the drone. Taking a deep breath and thinking about what to try next.

[chrisp]

That kills the 2 different size theory . Flowmaster delta-flow no drone / interior resonance .

[Sirrotica]

If I were you I'd try the hang on dampeners/weights such as ford uses on the pipes in front of the mufflers next if I were you, probably the next easiest route to try. I'd clamp them on so they could be moved easily fore and aft, or switched side to side for tuning purposes. If they don't work on the front pipes I'd try them on the tailpipes too.

[VAB5]

Based on this thread at the Mercury Marauder board, I ordered a pair (RH and LH) of Ford exhaust dampers.

The Marauder exhaust is totally different in terms of size, resonant frequency, etc., and these dampers were probably engineered specifically for that exhaust, but it's worth a shot. They are held on with a U clamp, so I can move them around.

I found a thread on the Porsche board where someone band clamped a small sledge hammer to his exhaust as a test and it got rid of his drone. That gives me hope.

I'll post my results.

[android 211]

Looking at undercar photos of cars for sale and in magazines sometimes it appears the headpipes aren't as straight or direct as they could be; neither do they mirror each other. Perhaps the factory wanted the headpipe length to differ to help quiet the car down; avoid resonance. I have a 500 Cadillac powered Cutlass with cast manifolds. Originally I had a 2 1/4" system with Dynomax 14" mufflers and tailpipes. No cats, no drone. Now the headpipes are 2 1/2" with an X pipe. Its quieter and still no drone. Guess I was lucky.

[rad400]

I have drone 2 1/2" duals no "X" with flow masters and have the drone. Some day want to try Hooker max flow mufflers.

[zeebo]

its not a pontiac, but since its about exhaust..my 96 caprice with factory duals has a weight bolted to the front pipe at the trans on the pass side..also has big 19" mufflers and resonators. so gm must have tried weights to eliminate drone on some cars....

[Tim Corcoran]

I have a 67 LeMans with a 441, RA style exhaust manifolds, 17749 Dynomax mufflers and 2-1/2" pipes all the way back, no X pipe or H pipe. There is no drone at any speed and the noise level is very pleasant. Not as quiet as a factory but you can listen to the radio. I have never had an X pipe so I can't comment on that. Forget about 3" exhaust and run your exhaust all the way back and you will have a more enjoyable ride. You will gain very little if any by going with 3" pipes.

[VAB5]

Finally getting around to posting results of the Marauder dampeners. Since they were originally meant to be mounted to flanges, I had to bolt some L brackets on them in order to test mount with U bolts. I mounted them just in front of the mufflers.

With the dampeners in place, I noticed a more hushed tone. Still some drone, but as I noticed when I removed the dampeners, it was much less droney with the dampeners.

Next step is to get them welded on. Using U bolts, the bolts hang down way too far and rub on speed bumps.

[Joel Koontz]

Has anyone tried two X Pipes, or two H Pipes, or an X Pipe and an H Pipe?

[zeebo]

yeah..goerlich made i believe 24" and 30" case mufflers for a while, tho im not sure if they would fit under our cars..id have really liked to try them...may have to go with four mufflers to quiet it down.