[Sirrotica]

Originally Posted by FrankieT/A

The drone is not from the actual installation in my opinion but rather the sound waves. So I don't think hanging weights on the exhaust is gonna help. I would think weights would dampen vibration in the system causing metal fatigue. When you use an S type turbo style muffler it actually lengthens the exhaust system. The exhaust system thinks the muffler is triple the length. The drone is from sound waves getting out of phase with each other. The exhaust as a system needs to be tuned, just like the analogy ericwy used. Sirrotica is right about resonators to a degree. I was in the muffler business for some years and really the only cars that had resonators for the most part were the luxury cars, but i feel that was mostly to reduce noise further and not because of drone(Brad, thats just my opinion). I can tell you that back in day( before Dr. Gas and his X pipe) putting in H crossover eliminated drone a lot of the time. From all posts of this thread, the only people that were successful at eliminating drone changed to a different muffler. Turbo mufflers use a parabolic system to cancel out sound waves instead of just a packing to absorb noise. Back in the day I used turbo mufflers because Flo Masters weren't invented and I used to blow out exhaust manifold gaskets(Ram Air III manifolds) left and right. It was driving me crazy!!! When I put on the Flo Masters I never blew an Ex. gasket again. I like the way they sound so I put up with a little drone.

Just a point here about resonators, 65 GTOs used a small resonator made into both tailpipes, 66 GTOs used resonators on both stick and automatic cars and 1967 they only used them in automatic cars. I imagine there was a reason they were used and in 68 they were dropped. They then used a tuner pipe similar to the J pipe to cancel out unwanted sound waves on the right side only tailpipe. In 1969 resonators returned and then in 1970 they disappeared. I don't know if it was because of bean counters or not. I have never read an explanation for the change.

Since these pipes didn't last long they were replaced with aftermarket pipes with no resonators. I never knew Pontiac used so many resonators on GTOs and I worked at a Pontiac dealer in 1970 and either forgot about the factory resonators, or the cars I saw already had them replaced with aftermarket tailpipes. Look at the Gardener exhaust website and they show all the different OE tailpipes with resonators and tuner pipes for GTOs, there was a sound problem on these cars ever since they were made new.

http://www.gardnerexhaust.com/gto-exhaust-systems.html

It would seem there was a legitimate reason that Pontiac felt the need to use them in 65 and not in the previous years and delete their use in 70. Resonators are used to tune out objectionable sound waves and are only 1 tool to use. Just another FYI in 2005 the GTOs again used resonators and to me the stock 05-06 GTOs are just fine in the noise department not going to bring the eye of the law but a nice deep tone to let you know it's not a FWD GP even though they look similar.............LOL

I read about the J pipes and that is a very interesting concept too, from reading about the success it seems like a very useful tool, much mathematical formula use to calculate the correct dimensions for maximum sine wave cancelling. It's interesting also that they are tunable by adjusting the plug in the end of the J so you can get rid of the drone even if your using a modified form and not stock pipes.

The F body cars I believe Pontiac used the transverse muffler to cancel out sound by bouncing the waves off of each other. When the pipes are run with separate mufflers in an F body the drone appears and some other form of cancelling it out needs to be implemented. On my own cars and some customer cars I've tried to keep a transverse muffler and if I didn't, I used an H pipe to keep the undesirable sounds in check. I have even used an H pipe with a transverse muffler to add some performance and make the car somewhat of a sleeper by keeping it quiet.

To this point I have never used an X pipe, it may be that they don't cancel the bad sounds out as well as an H pipe does. I plan to run one on my next car so I may have to sort out the differences between H and X pipe sound wave cancelling differences.

[FrankieT/A]

Well Brad you are obviously older than me. Most of the cars I worked on we're from the '70's and up, with exception of my own '60's cars and friends and such. By then they were 10-15 years old. And being you are from the north, you saw a lot more salt then I did. I remember when northern cars would come in, we had mixed emotions, everything was always a mess and usually required a lot more work, bolts breaking, more parts and generally a PITA. On the other hand, we'd be ringing the register.

[Sirrotica]

Originally Posted by FrankieT/A

Well Brad you are obviously older than me. Most of the cars I worked on we're from the '70's and up, with exception of my own '60's cars and friends and such. By then they were 10-15 years old. And being you are from the north, you saw a lot more salt then I did. I remember when northern cars would come in, we had mixed emotions, everything was always a mess and usually required a lot more work, bolts breaking, more parts and generally a PITA. On the other hand, we'd be ringing the register.

Be 60 in Jan so I'd guess I'm older..............

I lived in Erie Pa and exhaust lasted maybe 4 years in that environment if you were lucky. Lots of exhaust was replaced early on in these cars lives and yes rust belt cars require special tools to work on them, a torch will get almost anything apart one way or another. Probably why I am fairly proficient with a torch and can remove bolts from exhaust manifolds with one without hurting the manifold. I can also weld with an oxy-acetylene torch which is becoming kind of a lost art anymore with the advent of MIG welders. People think I mean braze with a torch as some think you can't really weld with a torch, can you?......LOL

[wrenchmen]

Would like to take a poll as to who has sound deadener on the floor and who does not , i believe this may play a role in the drone / interior resonance .I have the peel/stick foil faced & have 40 series Flowmasters on a 461 roller Kaufman headed tri-power 64 GTO , no drone @ all tailpipes exit behind tires @ the side .

Forgot to add that I also gutted my interior, added peel n stick to all floor sheet metal and up the rear sides including behind the rear seat and under the package tray.

I also hung a very heavy piece of jute type insulation behind the rear seat back.

All that work did not seem to make any noticable difference to the exhaust drone inside the car.

[FrankieT/A]

Gotcha Brad, being in the exhaust business does make you proficient with a torch regardless of location, we used to call it the "Hot Wrench". LOL My Ex is from Stoneboro, PA. about an hour south of you. I always loved that country for riding (Harley) and driving. Shame I have no reason to go there anymore. I used to spend a lot of time there. Married 18 years.

[rexs73gto]

In one of my last posts now if your taking a poll about insulation or not, I have the peel & stick type also & still have the drone problem with the X-pipe to. I'm going to try to get the tail pipes on next week & see if that helps. But from all the posts here I'm not sure it's going to make any difference at all. If it doesn't I'm going back to a qiute style muffler to absorb all the sound to see if that helps. By the quite type I mean the type that you get at the local parts store for a stock replacement type muffler. I have to get rid of that drone inside the car. Like I said before I've had the car since new (73GTO) & have never had this noise. I've had header, exhaust manifolds, & always had duel exhaust, but never had it until I put on an X-pipe. I just makes me wonder as I asked before is it the X-pipe.?????

[Sirrotica]

I think it may be a great help if someone from the tech staff from PYPES, or perhaps C. Cass himself would chime in here with some remedies to some of these problems facing members here on this discussion. They have a possibility to sell some parts here if they have some answers to the questions being asked and I'm sure they'd be happy to sell some of their inventory.


Anyone from PYPES want to join this discussion and maybe add some more practical information here?

[ericwy]

Originally Posted by rexs73gto

In one of my last posts now if your taking a poll about insulation or not, I have the peel & stick type also & still have the drone problem with the X-pipe to. I'm going to try to get the tail pipes on next week & see if that helps. But from all the posts here I'm not sure it's going to make any difference at all. If it doesn't I'm going back to a qiute style muffler to absorb all the sound to see if that helps. By the quite type I mean the type that you get at the local parts store for a stock replacement type muffler. I have to get rid of that drone inside the car. Like I said before I've had the car since new (73GTO) & have never had this noise. I've had header, exhaust manifolds, & always had duel exhaust, but never had it until I put on an X-pipe. I just makes me wonder as I asked before is it the X-pipe.?????

I don't have any sound deadening material in my TA. Just carpet and its jute padding.
I think the bigger pipes also are more likely to have drone.

I got rid of the drone by isolating the exhaust from the body, dampening its natural harmonics and putting alot of obstacles in the way with several transitions from smaller to larger and larger to smaller pipes :
1. 1-5/8" header tubes,
2. 3"collector,
3. reduced to 2.5",
4. back up to 4" through the Cats,
5. reduced again to 2.5" and through the X-pipe and to mufflers
6. 2.5" Dynomax STs,
7. reduced again to 2.25" OEM Walker tailpipes
8. Exit Chrome splitters below the quarter before the bumper

Not as quiet as my wife's minivan and not optimal for performance, but I can drive it all day, and now I hear every rattle and squeak that was being drowned out.
It actually drove me nuts for the first few weeks until I was able to ID each little rattle or sqeak.

[rexs73gto]

I'm not sure that anyone from pypes will anwser because that if it is the problem would be putting the blame on them & others like them , so there going to stay out of it. If it was a problem that was created by the use of one of there products could you think how much it would cost them to fix all the cars out here with the drone. Plus this is just us now & there has to be alot of other cars out there that are having the same concerns. I think what will happen is someone will come out with a real fix & that will cost us more then to fix which will make them a lot more money. The reason I say this is the new cars that have the same size big exhaust like the new charger & camaro have huge exhaust & they don't have this drone problem WHY NOT??????? They run cross over pipes & 3 " exhaust & even true duel exhaust now. Why no drone.??? there big hp & big inch with no drone..??? WHY????? Plus there very quite.

[Jack Gifford]

What strikes me about the "drone" situation is how often (very!) the car manufacturers need to resort to an additional muffler (so-called resonator) to accomplish the desired in-car quietness.

[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.

If the right and the left sides are different the sine waves don't amplify as they are not the same frequency, so Pontiac engineer in their wisdom made the mufflers different lengths and sizes so the sound waves didn't mirror each other. It also seems that X pipes make this phenomenon worse, just switching one muffler may cancel out the drone.

Another fix was to build a pipe that looks like an H pipe and install it behind the X connecting both pipes together. The pipe is not open in the middle though it has a barrier wall inside the pipe and is not in the middle, it is about 1/4-1/3 of the way from one end causing unequal length chambers for each pipe also causing the waves to be at a different frequency. It seems v6s are even worse than V8s are and this is how some of the HP V6 guys fix the drone and it also works for V8s. They call it a center resonator chamber and it looks fairly easy to build and install.

http://www.allfordmustangs.com/forum...s-p1010351.jpg

http://www.allfordmustangs.com/forum...s-p1010356.jpg

Some other info was the J pipe, resonators, a glass pack towards the end of the system tailpipe area, the weights that ford uses welded on the pipes at different points and different length arms and possible different size weights. The main theme here is to make the system not mirror the other side so the waves change. It evidently can be accomplished in a variety of ways. I hope this may be of some help in enlightening about what causes this problem.

After thinking about this center resonator chamber if I were to build one I would also maybe vary the pipe diameters as well as the wall in the middle to make them as much different as possible, the shorter side 1 3/4 pipe and 2 1/4 on the long side.

[Sirrotica]

I also found a formula to calculate a resonator pipe chamber that would be added to a pipe on a single exhaust system that has drone, or one side of a dual system.

Frequency = [(drone rpm) x (#of cylinders)] / 120

= [ 2000rpm x 8 cyl ] / 120

= 134 Hz

Resonator Frequency = [ (Speed of Sound @ 150 deg F) / (Length of Resonator) ] / 4

Set the Engine Frequency = Resonator Frequency and solve for the Length of Resonator.


I assumed exhaust temps of 150 deg F for Speed of Sound = 1210 ft/s
When you do you will get ~2.25 ft

So you will "T" a 2.25 ft (24.25") long off each over axle pipe.

It seems some turbo diesels with single exhaust also experience the drone too along with some inline engines in certain makes of cars.

[ta man]

Originally Posted by rexs73gto

I'm not sure that anyone from pypes will anwser because that if it is the problem would be putting the blame on them & others like them , so there going to stay out of it. If it was a problem that was created by the use of one of there products could you think how much it would cost them to fix all the cars out here with the drone. Plus this is just us now & there has to be alot of other cars out there that are having the same concerns. I think what will happen is someone will come out with a real fix & that will cost us more then to fix which will make them a lot more money. The reason I say this is the new cars that have the same size big exhaust like the new charger & camaro have huge exhaust & they don't have this drone problem WHY NOT??????? They run cross over pipes & 3 " exhaust & even true duel exhaust now. Why no drone.??? there big hp & big inch with no drone..??? WHY????? Plus there very quite.

My car is over 500hp three inch exhaust,Pypes X crossover,2.5 Dynomax Ultraflow Mufflers,2.5 tailpipes with exhaust tips that exit just rear of the bumper.It is a 1980 Trans Am A/C car with the full insulation and dampening..no drone actually pretty quiet going down the highway.

[wrenchmen]

Good info there Sirrotica. I would have tried that H style pipe behind my X-pipe before I replaced the Spin Techs....would be a very easy mod.

I loved the sound with the Spin Techs and had many compliments from random people,
some very excitiedly yelling out as they drove by how awesome my car sounded!

The drone was just too much. RARE (Ram Air Restorations) where I purchased the whole system, told me those mufflers should have no drone. At first I thought maybe
I installed them backwards, as the inlet and outlets were not marked, But I removed a pipe and looked inside, verifying they were correct. I should also add that the salesman at RARE was willing to exchange the mufflers, but I didnt follow through on that, as I had welded on swivel type connections to them.

The X-pipe RARE sells appears to be different from other X-pipes, they claim it is from NASCAR engineering and is a superior design....maybe this adds to the drone effect?...I dunno.

Almost forgot to mention that in my drone free quest, I purchased a pair of Hedman Hot Tips,
small 9" resonator chrome tips...litlle glass pack exhaust tips.
like here...http://www.jegs.com/p/Hedman/Hedman-...69187/10002/-1
Bolted them on and guess what...absolutley no drone. BUT my car now sounded like crap! They really drastically altered the sound. For a while I would just bolt them on when we were taking a long drive, but that got old real quick and also in a short time, the chrome peeled.

As you can see, I did a helluva lot of stuff to try and eliminate the drone AND keep a decent strong sounding exhaust note. I am happy with the DynoMax VT for now.
Another added benefit is they seem to not reject as much heat onto the rear floor and into my car as the SpinTechs did. The SpinTechs rejected a ton of heat, and I would think that means they didnt flow as much as the DynoMax VT's do.

[Sirrotica]

There are tons of people on the net complaining about Spintech mufflers, and if you look they are just as many complaining about every other HP muffler made. As I said in an earlier post this isn't a new phenomenon it's a problem Pontiac engineers knew about long ago and used non mirrored exhaust systems along with resonators, resonator chamber tailpipes etc.

I believe there are more people modifying their exhaust and there are tons more aftermarket parts available now than when I first started messing with cars. There were headers on a few street cars, glasspaks, and straight thru mufflers. There were no 3 inch systems, no X pipes, H pipes weren't known well then either. If you put glasspaks on your car you knew it was going to be loud and obnoxious and you expected it. In the mid 70s Turbo mufflers became the big deal and were for along time there were glasspaks or turbo mufflers. Turbo mufflers were the first ones I ever used that gave me a drone on my 75 T/A and while it was fine in town, on the interstate it sucked to drive 40 miles in it.

The more people stray from the engineered factory systems the more problems they seem to run into. There is more thought into the factory engineered systems than we realized

[ERIC AULL]

For consideration....on boats that have twin engines, when both engines are synchronized to the same RPM....one can hear a slow pulsing drone.....gotta be due to similar/same sound waves like Sirrotica says....makes sense to me. Hence, a difference in length,size, etc on each side of a dual exhaust, SHOULD "break the drone up"....

[drtracer58]

Does anyone involved use oval Exhaust ?? I am assuming it doesn't make a difference ???

[wheelspin]

Like others here, I experienced major cabin resonance after installing a home fabbed 2.5" mandrel bent exhaust system (pre-Pypes era) behind the Doug's headers in my GP listed below. I tried 3 different higher flow muffler pairs, all longer case designs, with no significant change in a drone that heavily buzzed the GP metal dash and console to the point that I stopped driving it . I rechecked the exhaust mounts thinking that one had come loose causing metal to metal contact, but everything was in good order. Than I remembered mounting a lot of aftermarket motorcycle exhaust systems and how the pipes were similar to a tuning fork when it came to finding a 'happy spot' that provided a buzz free motor. Sometimes it required loosening the head pipes while tightening the rear hanger, or vice-versa.

Following the factory's lead, I added two bullet type muffs (think Cherry Bombs) installed in the tailpipes on each side of the fuel tank thinking that additional weight in the lengthy GP exhaust system should change the harmonics. VICTORY! To verify my finding I reinstalled my favorite Goerlich muffs as recommended by Jim Hand and the cabin remained buzz-free more in keeping with the GP's personal luxury mission . My take; the bullet muffs extra weight in the tailpipes eliminated the cabin resonance not the extra muffling.

[PontGuy]

I probably had a ton of drone on all the cars I built during my early years, but they were so loud that I couldn't hear it!

69 Lemans vert now, same as the OP. Its even factory red like VAB5's, as if color could make a difference. But then again we are throwing everything on the table.

The original system with a nicely-cammed 350 engine was factory logs, custom bent pipe (can't remember either 2" or 2-1/4"), welded from end-to-end with no X or H, Flowmaster mufflers, and tailpipes straight out the back with no tips. It droned so bad from 2000-2500 RPM that it would rattle my teeth. Took it back to the shop after the first week and had straight thru resonators installed in the main pipes. The exhaust was quieter, but it still droned to the point of irritation at exactly the same RPM range.

New system with mildly built 455 engine is 2-1/2" RARE manifolds, Pypes 2-1/2" system with X and 17449 20" Dynomax mufflers, and tailpipes straight out the back with no tips. Just a bit of a drone (non-issue) from above idle to around 2000 RPM. Started with band clamps everywhere, then had the whole system welded up. No difference except the leaks are gone.

The new system is much quieter (as hoped for and expected), but I found it interesting that the drone RPM is different. Does engine size make a difference with respect to drone?

[Sirrotica]

Harmonics of sine waves is what causes it, as has already been said the sides should not mirror each other in length size and muffler. There's plenty written about exhaust drone on the web as to not go through the whole thing here. Engine size probably does have something to do with it as a larger engine is sending more gas through the system.

It can be tuned out if you follow the suggestions and you'll have to do some reading on your own to get all the things that can effect it or get rid of it. No two systems cars or engine are exactly alike so one size does not fit all, just going to have to read up on it and pick the one that you think will work in your instance.