exhaust drone fix

[don duick]

i have a 70 charger with a 440 and 727.  headers, 2.5 dual exhaust with h - pipe and straight through mufflers,  had an unbearable exhaust drone that bad to the point where I could no longer drive the car. Every time  after a drive, my ears were ringing. I tried 2.25 baffled mufflers  with 2.25 tailpipes still had drone and lost a lot of power. went back to what I had.  I discovered on a ford f100 forum "closed pipe resonators" I was sceptical but in desperation gave them a try and holy F@#% do these things work. about 90% of drone gone. Feels like a totally different car. I read that these  resonators do not make the exhaust  quieter just change the tone. In my case they also made the exhaust a whole lot quieter also. I now can hear the radio and talk to the passengers. A closed pipe resonator is just a piece of exhaust pipe that has to be 28 inches long and capped at one end preferably the same diameter as your exhaust pipe [ I used 2 inch as it was easier]  there is a formula that determines the 28 inch length but we wont go into that, trust me this lenght works. the article I read stated that it is important that it not be any shorter as it will not work as well. hears how to install it. If using a 2 inch pipe, cut a 2 inch hole anywhere in your tailpipe where you can fit this under your car. this 28 inch pipe is welded on to your tailpipe at 90 degrees don't forget to cap off the end. I put mine on top of the  tailpipe where it goes over the diff and they run parallel to the diff and cross over each other. this is why I used 2 inch pipe as 2.5 pipe may not fit. To weld them to your tailpipe first weld a short piece that is flared then slide in the rest of the pipe and hold it on with a clamp. If you cannot fit a straight pipe, to your tailpipe, then  start it off at 90 degrees then you can install a bent pipe to fit your car they must be mandrel bends, The theory behind this is simple. sound moves in waves at a certain wave length where the harmonics  in the exhaust match the harmonics of your motor  at a particular rpm usually between 1500 and 2000 rpm you get the drone. the closed pipe resonator breaks the sound wave alters the frequency of the sound wave and cancels the drone. as the sound waves pass through the tailpipe the waves travel down the resonator hit the end and bounce back into the path of the next wave and alters its frequency. This was discovered about a hundred years ago by sound engineers in the making of musical wind instruments. 

[Bob T]

Hmm, interesting, and yes sounds like a tested and proven fix, good.
I remember experimenting with different length intake tubes and homemade manifolds for a set of Weber 45's after talking to an old guy about wave length / harmonics / interaction , learnt what worked and what killed it stone dead after a certain rev level...

  Welcome, by the way too, we all love the pictures, maybe you could put up a few of your 70 when you get a chance.

Bob

[myk]

Exhaust drone?  Are you running Flowmasters?

[don duick]

 no mercury, don't know anything about  mufflers just got whatever was available at the local exhaust shop had no idea which ones to get and did not want to risk spending lots of money trying out different ones. do you know of a particular brand that flows well without drone? I also tried 3 inch dynomax vt got them cheap, ok at low speed but when I floored it they were way too loud  tried walker 2.25 mufflers but lost a lot of power and they also had drone

[myk]

I would've recommended something from Dynomax but looks like that didn't work out for you.  I dunno man; one of the caveats of driving these cars is they aren't subtle about anything...