I just had a brand new custom exhaust made for the Comet. The shop did a beautiful job, but I'm getting a deafening drone at highway speeds. The exhaust is all 2" stainless, and has one pipe coming off the stock I6 manifold, then splitting next to the transmission and running duals all the way to the rear. The mufflers are Smithy's 26" gl***packs, mounted about under the rear footwells, and they put slash cut megaphone tips on it. I've cut the tips off (didn't like the look anyway) and it had only the tiniest effect on the noise. The drone happens under any significant throttle and on the highway, it is the sort of drone that doesn't seem to be coming from one particular place but instead feels like it's vibrating your head. I've gotten all sorts of advice from changing out the mufflers, to goign with a single muffler, to moving them to the ends of the pipes (stock muffler location was at the far end next to the gas tank). Any advice you guys can offer would help. I'm looking for advice before I go back, so I have a better idea what modifications to have them make to the system. Photos:
umm, thats not stainless! Its aluminized steel. But beyond that there will be someone who will chime in here in a second who is an expert on the subject, but I think you are fighting a resonant frequency. I'm not qualified to explain it! I just had exhaust run under my falcon, and was worried about the same issue. The last time I put an exhaust under one of these it was real buzzy and droan like. This time I ran a single pipe all the way back, and had them split right after the muffler, which was located under the rear seat. And then they split out into separate tailpipes. I love the way it sounds!
Nice detail work under the car! Very tasteful. Frankly, You're gonna get some drone- it is a by product of the giant tuning fork You've created. You won't be able to completely remove it, but You can move it up or down the powerband. Alot of guys here running straightmotors run true duals. the "trick" is to run straight pipe on 1 side and a muffler on the other. Might give that a try. Gives the exhaust a nice "slap and tickle" when rapped out.
Definitely resonance. The path of least resistance it seems to me is to change the mufflers, since it looks like they're clamped on. There's my $.02.
I had the same thing with a single exhaust Flowmaster setup on the Mustang. At multiples of 1500 rpm the exhaust sounded like someone blowing across the top of a large jug. Made my brain itch. Really annoying. I switched to true duals and the noise went away. One easier way to fix a problem like that is to add a resonator. You can do that by putting them either in the tips or adding one ahead of the Y-pipe. A small tubular gl***pack often works pretty well and you'll see them on a lot of OEM systems for the very same reason. Another possibility is to add a resonance chamber. A closed end pipe T-eed into the system can tune the resonance, much like tuning a wind instrument. By doing this you can alter the sound of the system and BMW uses the principle to tune their exhaust note. But I don't know of a good way to easily predict how much of an effect such a chamber might have. Maybe someone could chime in.
I would try different mufflers. I have basically the same set up on my falcon with dynomax turbos for mufflers. They use to dump just before the rear end but now exit thru bellflowers. Has a great sound (alot of people think the car has a 289 in it) I dont have any kind of droning etc.
I take it this wasn't doing this before (the new exhaust) but it was running / driving? Looks like 409 stainless on my monitor (***inated, with the streaks).
I fought the same thing on both my Ranchero and Comet Wagon. Both had true split headers on the 200 six, ****** on one, Clifford on the other. The Ranchero was a daily driver so I went to a single muffler - drone gone! The Comet looked pretty much like yours and different tips, mufflers, placement etc made little or no difference - it always droned. Now it's droning in New Zealand!
Some sixes do set up an amazing exhaust vibe. A 220 International is all but impossible to drive with no muffler, it creates actual pain! Ears, chest, gut, the whole works.
im surprised an exhaust shop wouldnt realize that the exhaust sytem set up this way would produce this type of effect
I have the same problem with a dodge pickup with 318 it has a short single custom exhaust that exits in front of the rear wheel. I think it has a flowmaster on it. it droans about 65-75 on the interstate but is good below it. So i don't know if the pipe length will do anything for it or not.
that was my first thought as well when i saw the pics. maybe improbcat could try clamping a bar from one pipe to the other in front of the fuel tank as a test to see if that helps the problem.
It didn't drone before this went in, but what was under there before was a single-pipe system that was a cobbled together mess. When that rotted out I had this put in. LUX BLUE/ray: if the clamped bar helps, should I have them put in an H-pipe kinda setup that links the two pipes in front of the gas tank? Von Rigg Fink: I got the impression they mostly do V-8 cars, so they might not have realized what this would do with an inline. Thanks for all the suggests/ideas guys!
Other thoughts: On some OEM vehicles they use different size muffs on each side. That tends to counteract the resonance. Another easy test would be to plug or restrict one side to see if that might make a difference. If it does, you could pretty easily slip a baffle into one side or the other.
What about replacing the Y-pipe with a front muffler? That would work as a chamber, might help out some.
The easiest way to solve this is to run a single muffler before the split. That is- move the "Y" towards the rear axle (one cut), and fill the void created with a single Smithy's muffler. Since the existing dual mufflers are bolted, and the exhaust route(s) look pretty parallel, it would only involve a single cut in front and then two splices were the mufflers are now.......
Traditionally, 2 inch. I use 2 1/2. (simply because that's the size Bends I keep in stock. ) Before we get into the great "that's too big" debate, realize that even the nicest split manifold isn't going to flow super huge numbers, anyway.
I bet you have one of those pipe hangers grounding metal to metal instead of on the isolation rubber. Maybe only when the engine is torqued over on it's mounts at the RPM you hear it Seen that cause drumming droneng sounds before
LUX BLUE/ray: if the clamped bar helps, should I have them put in an H-pipe kinda setup that links the two pipes in front of the gas tank? I doubt a balance pipe would do a bunch in this application other than make it difficult to access the gas tank. -the exhaust not is balanced because it is singular up to the split. What you need to do is take some out of 1 leg of the fork- either by removing/changing a muffler, or increasing the backpressure to 1 muffler with a baffle, or a reversion cup. Whatthahell is a reversion cup? Check this out. Next time you make it to Your local grocery store, hit up the cookware isle. You are looking for a custard form. (basically, a little stainless steel bullet with a flat bottom.) it ought to run you around 35 cents. Take it home, and cut the flat bottom out of it. The hole should be around 1 1/2 inches in diameter. if the cup is too large to fit inside the pipe, cut a slit down the side squish it together. the key here is the hole in the bottom. it has to stay in the 1 1/2- 1 3/4 range. Remove the front of 1 muffler. slide the bullet into the pipe with the "pointy end" facing TOWARD the muffler. (sometimes, You can get it into the muffler if you talk to it sweet and buy it dinner first.) slide the muff back into place and clamp it down. what this does is 2 parts. #1- it effectivly reduces exhaust pressure to that muffler. This will change the tone of that muffler. #2- It keeps the exhaust pulse from making it back "up" the pipe, helping to reduce droning. ( it sometimes makes the motor run a bit better, too.) Good luck! Lux
I like Lux Blue's idea, but you could also try moving one of the mufflers forward or back about a foot. Problem is it might just change the rpm where it drones, and would be trial and error.
how many miles are on the system? i would check all the hangers, make sure they arent solid, they are all isolated by rubber. look into, either one flex joint i nfront of the Y or one on each side after the Y. i dont really like that Y pipe, it could be doing funky things to the sound, but i wouldnt guarantee its the culprit. mufflers do change thier tone after a few heat cycles and as they get some miles on them. id drive it for a while before changing anything.
Fifty or less, I can't drive it far with the drone like it is. I'm going to try putting a baffle in one pipe, and/or LUX's reversion cup and see what that does. If it doesn't make a significant improvement I'll probably end up getting it re-configured fro one muffler and splitting after the muffler.
it will definitely change with more miles and more heat put through the mufflers. i cant imagine it not being driveable, i used to have 3" 2 chamber flowmasters with no tailpipes or even turndowns on my dart and i didnt think there could possibly be any more resonance than that. the hairs in your ears would constantly tingle and vibrate. i used to like it. the i built a new system with some dyno max ultraflows afte ra few years and i got tired of it, first 1 1/2 hr ride i went on, it had terrible resonance. i was pissed after the money spent and the time involved, mainly to get rid of the f-master drone. after a few long rides there is hardly any.
ive used a pair of purple horney gl*** packs on a v-8 two differant times and had a terrible drone,are these known for that?once on someone elses car and once on mine.cjc
Try adding weight to the system. Clamp weight to the system and move it back and forth. I would start right around your y pipe. Alot of times a resonance will come from a vibration through the system especially with 409 ss. 409 is more brittle and harder than a 304 or aluminized. Moving and adding weight to certian spots may cure this. Inline sixes are notorious for this. Ford has used weights on the exhaust for years. Those rear hangers are put on wrong. Your exhaust should be allowed to move back and forth. Those are going to put your system in a bind. You may be allright though. 409 won't grow quite as much as mild steel.
Like Mustang Six said, factories often use(d) multiple mufflers on exhaust pipes to damp resonances. In the days before cats were added to exhaust systems, it was pretty common to see one or two small resonators in addition to very large primary mufflers in each pipe of an exhaust system. XKEs used split manifolds and dual exhausts. They had a muffler and resonator on each pipe and they always sounded great. Try replacing your tail pipes (where they're flared out already) with ones that have little resonator mufflers in them. You might find that does the trick and nothing else in needed.
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