Ed
76 with exhaust harmonics (I think?)
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Joined: Aug 2010
Posts: 57
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From: Denton TX
76 with exhaust harmonics (I think?)
I bought a 76 a couple months ago and I am still "getting to know her". The first few times I took it out on the road, I noticed mean vibration that sounded like it was coming from the right rear wheel well. It only occurs from idle up to about 25 or 30 mph. I read a lot of posts on here and then did some more investigating. After a few more trips and then just starting/reving it in the garage a couple times, I discovered it has nothing to do with driving.
From about 700 to 900 RPM it sounds deafening but then smooths out nice at higher RPM. I think there is harmonic vibration in the exhaust? I have heard of this in twin prop aircraft, is it possible in a car? It has a flowmaster exhaust with the original exhaust manifolds. I am thinking about putting on headers to help reduce a little noise and maybe some heat. A friend with a 71 said he connected both sides of the exhaust with a tube across the middle of the car, but I don't see anything like that listed on the parts sites. I guess it is just a strait tube welded between each side. Anybody have advice or info? Thanks in advance.
From about 700 to 900 RPM it sounds deafening but then smooths out nice at higher RPM. I think there is harmonic vibration in the exhaust? I have heard of this in twin prop aircraft, is it possible in a car? It has a flowmaster exhaust with the original exhaust manifolds. I am thinking about putting on headers to help reduce a little noise and maybe some heat. A friend with a 71 said he connected both sides of the exhaust with a tube across the middle of the car, but I don't see anything like that listed on the parts sites. I guess it is just a strait tube welded between each side. Anybody have advice or info? Thanks in advance.
Burning Brakes
Joined: Dec 2007
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In my experience, larger diameter exhaust pipes increase exhaust note and contributes to 'drone' and do not contribute to noticible performance increase as a daily driver. I am considering removing the 2-1/2" system that was installed on my car before I bought it and going down to 2". OR: install the factory mufflers on my 2-1/2" system. NOt sure my gently modded 350 pumps enough air to properly fill up 2-1/2" pipes.
Race Director
Joined: Jul 2001
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Harmonics in a multi engine aircraft are due to slight mis-matches in engine speed, obviously not the same as a single engined car. Your noise is not unusual for cars with flowmaster mufflers, an X or Y pipe might help but the overall exhaust level might still be too loud.
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Joined: Aug 2010
Posts: 57
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From: Denton TX
Good to know.....anybody else add 2.5 headers and have the drone get worse? Or cured it with an X pipe?
Don't get me wrong, the car sounds great above 25 or 30 MPH....but sitting at a light or rolling in slow traffic it's painful. I bet it's not too bad sitting in a car next to me at the stop light, but there is a sweet spot in the middle of the cabin that resonates.
Don't get me wrong, the car sounds great above 25 or 30 MPH....but sitting at a light or rolling in slow traffic it's painful. I bet it's not too bad sitting in a car next to me at the stop light, but there is a sweet spot in the middle of the cabin that resonates.
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