Man, I must be getting OLD. Wife and I took the first real ride in my 39 Plymouth late this afternoon, after it stopped raining. Man, that was cool. Put about 50 miles on it. For those of you that don't know, it has a 3.9 V6 out of a Dodge Dakota. I'm running the V6 exhaust mainfolds with the emmision tubes blocked off. The driver side manifold has 3" spacers kicking it out away from the motor. There are new exhaust gaskets on both sides of the extension blocks. Out of the manifolds the exhaust (both sides) makes a fairly sharp 90 degree turn outward (I had to go outside of the frame with the exhaust). After the kick out they have about a 10" radious curve down and back. Up to this point the pipes are 2" with cut and welded factory turns (slightly small diameter on the tight turns, like the factory would have done.) At the point where the pipes level out they are 2" conduit, which measures 2 1/4 ID.(?) At the mufflers they have a step down to a 2" OD pipe and the mufflers are Thrush Turbo performance mufflers with 2" id inlet amd outlets. The Thrush mufflers are about 12" long, and there is nothing after the mufflers. The pipes and mufflers are under the running boards and the exit end of the mufflers are just in front of the rear wheels. I love the way it sounds at an idle, and it sounds great at wide open throttle. At cruising speed there is an irritating drone. Loud enough you can't talk. Really bugs my wife. After 30 years together, I need to modify the car's exhaust, cause I'm keeping her. I would like to keep the mufflers if I can, but I have to change the pitch or quite it down or eliminate the drone completely. Questions: Would a down turn at the end of the muffler eliminate or reduce the drone? Do I need to add full length tail pipes? Smaller head pipes? "X" pipe? What do ya think?Gene
First off, look for anywhere the pipe system might be touching the frame or floor and don't have any mount brackets going to the floor because they turn the whole car into a drum with you inside. All the mounts should be the "rubber bagel" or reinforced strap type. Had a friend who was touring with a musician who's wife had mufflers put on her 351 Mustang years ago and he called me and asked if I'd look at it becasue it was way noiser than before the mufflers were put on it. I drove it about ten feet and stopped and looked underneath. The nukeyoular scientists at the muffler shop had welded one end of a steel strap to the rear of the flow master and the other end of the solid steel strap to the middle of the floor under the rear seat!
Hmmmmmmm. Other then where they attach to the heads, the only brackets holding the entire exhaust stytem are steel brackets bolted to the running board brackets and held onto the mufflers with hose clamps. The pipes have plenty of clearance everywhere, I really dislike rattles.Can I get away with a strip of rubber between the muffler bracket and where it is bolted to the running board bracket? How thick of rubber would I need?Gene
If it's a solid bracket, that's probably a large amount of the noise. The insulation part of the tailpipe brackets you get at your auto supply store look like they were just a strip cut out of the sidewall of a non-steel belted tire. Sorta like the links on my "traditional" back door mat. Just go over to Auto Zone and look at a few different ones. Maybe you can use one as is or modify it for your purpose.
The bracket holding my mufflers up is a T shaped with a little dog ear at the bottom of the vertical part of the T. The top flanges of the T are bolted to the running board mount and the muffler is hose clamped to the dog ear. The whole vertical section is about 2 1/2" high. If I cut a chunk out of the sidewall out of a junk tire and punch a couple of holes in it, then slip it between the top of the T and the running board and bolt the whole mess back togeather will that help me or am I going to have to suspend the muffler from the rubber?Gene
Suspend the muffler from the rubber. Cut out the direct solid metal to metal to frame connection. Look under a "civilian car" Toyota, Honda BMW whatever and see how they are done. Some have an "L" or two welded or clamped to the pipe or muffler that just floats in a rubber donut. If you don't want a store bought bracket, put your McGuiver cap on.
If you don't want a store bought bracket, put your McGuiver cap on. [/quote] My McGuiver cap ain't worth a damn. Ha ha. I had it on when I came up with what I have. LOL.Guess I'll have to see what I can come up with. I only have 2 1/2" between the running board and the top of the muffler outlet pipe. Pretty well elimitated any hangers I ever had used before. Gene
On my El Camino I rotated the clamp part on the single rivet that holds it to the strap 90º so that the strap attaches at the side of the pipe, mounting it a couple inches higher than it would otherwise.
If you haven't already, invest heavily in Dyna-mat or some other sound deadener. If you still have a problem, move the mufflers back behind the rear axle. Getting the outlets away from the passenger compartment will help the most. If you've ever thought of redesigning the exhaust system, look carefully at the layout of a later model 'vette. It's one of the most efficient around and sounds great with almost any muffler.
Gene, What you need are the exhaust hangers for a 1975 Chevy Malibu. Check out the pictures: The two holes on the bottom connect to your exhaust system via a standard muffler clamp. Next these two guys go together and connect to the chassis. The tab that's now mounted to your exhaust system slides thru the rubber part.
run the exhaust out to the rear of the car , ending your exhaust under a running board is part of the problem
All very good suggestions. I have also seen sway bar end link bushings or shock absorber (dampeners for yall out side the USA and Texas) bushings (even used ones) work well for isolating noise thru exhaust hangers. Some cars develop a harmonic resonation at certain speeds. This can be a low, booming noise that happens when certain frequencies overlap. (In a car, this will happen at a certain speed, then go away as your speed increases... say it's loud between 30-40 mph, but almost silent by the time you're going 50 mph or so.) Making sure the exhaust exits out from under the car will help this a lot. If it's still unbearable, then look at putting in a crossover pipe.
Thanks guys, lots of good sugestions. I'm going to try some different hangers first, if that doesn't do the job, I probably will rethink the entire exhaust. This was a quicky so I could do a little driving. Not really in love with this setup, but hoping to at least be bareable through the summer. Gene
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