reducing back rap

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Darren

Darren

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Hey guys I got my 2 1/2" exhaust system finished with MagnaFlow muffler. The car is a 68 383 cuda 4 speed stock exhaust manifolds. I took her out for a ride and ran through the gears and I get lots of back rap and poping when letting off the throttle. So I added a H pipe lastnight it helped but still there. Before I research other mufflers is their anything thing I can do to eliminate the back rap. Thanks
 
I ran the stainless oval magnaflows (14" body) with straight 2 1/2" dual exhaust and just found them way to "blatty" and "rappy" loud when you shoved it and the revs got up above 3500 or so and the same if you revved up above that range then let of the pedal (as if letting off to shift) .... ended up sawing them off and buying dynomax super turbos which are better. I was looking for a sound comparable to the old $25 thrush turbo 400's of the day
 
I have been hearing lots of good comments about the dynomax ultraflow mufflers. Do the only come in 14" case
 
I like everything about the MagnaFlow minus the sound when you let go of throttle at high rpm in low gear. Like a popping sound. Like a dam Harley. Lol
 
lil red said:
"blatty" and "rappy" y
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Loud mufflers + long tail pipes.

Only way I know of is quieter mufflers, shorter tail pipes, or put mufflers closer to rear (impossible I know)

OR......

ad just about ANY resonator at the end of the tail pipe no matter how "ineffective" to take the "edge" off.

"We" discovered this in about 1967. Friend of mine had a 57 Chev with loud blown out "whistlee" glass packs. Found some junk resonators. INSTANT!!! mellow.
 
67Dart273 said:
Loud mufflers + long tail pipes.

Only way I know of is quieter mufflers, shorter tail pipes, or put mufflers closer to rear (impossible I know)

OR......

ad just about ANY resonator at the end of the tail pipe no matter how "ineffective" to take the "edge" off.

"We" discovered this in about 1967. Friend of mine had a 57 Chev with loud blown out "whistlee" glass packs. Found some junk resonators. INSTANT!!! mellow.
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good info....I remember running the magnaflows just under the cab with no tailpipes while going to the garage and it was loud but no "rap" ...then totally different with the stacks hooked up, same loudness but different when you poured on it
 
Fix the timing.
Fix the carburetion.
The throttle blades have to close, to leave a little square hole of transfer port under the throttle blades. Or very near to square. And no vacuum leaks, and no exhaust flange leaks, none. If the exhaust pulls fresh air into it, a rich mixture in there will re-ignite and burn, making a lot of heat and often,noise. Ie pops.
 
AJ/FormS said:
Fix the timing.
Fix the carburetion.
The throttle blades have to close, to leave a little square hole of transfer port under the throttle blades. Or very near to square. And no vacuum leaks, and no exhaust flange leaks, none. If the exhaust pulls fresh air into it, a rich mixture in there will re-ignite and burn, making a lot of heat and often,noise. Ie pops.
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Thanks good info.... will check out a few of those.
 
Still have the Sonic Turbo mufflers on my car that I put on in 1988. They are connected to 2 1/2 inch pipes with a b pipe. They have a nice deep sound with no popping the throttle is released.
 
AJ/FormS said:
Fix the timing.
Fix the carburetion.
The throttle blades have to close, to leave a little square hole of transfer port under the throttle blades. Or very near to square. And no vacuum leaks, and no exhaust flange leaks, none. If the exhaust pulls fresh air into it, a rich mixture in there will re-ignite and burn, making a lot of heat and often,noise. Ie pops.
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I like the way you think AJ. :D
 
AJ/FormS said:
Fix the timing.
Fix the carburetion.
The throttle blades have to close, to leave a little square hole of transfer port under the throttle blades. Or very near to square. And no vacuum leaks, and no exhaust flange leaks, none. If the exhaust pulls fresh air into it, a rich mixture in there will re-ignite and burn, making a lot of heat and often,noise. Ie pops.
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Where does the dashpot on the carb come into effect. It is a 4 speed car. Is the purpose of the dashpot to delay the closing of the throttle blades when suddenly releasing throttle to prevent engine stalling?
 
You got it.
Now if you have one, get rid of it. Its actually a pollution control device, to clean up the exhaust. No sbm I have ever owned needed it as a anti-stall device, period. And by delaying the closing, it sometimes also causes the vacuum advance to stay energized too long. This can make the car behave oddly when coming to a stop.It also delays engine-braking so your head dont hit the windshield or some sucha thing. Which sucks when you're trying to do bunny hops and scare your passengers. Kids love that! My wife hates it! Yeah I know; grow up AJ. I used to hear that a lot.lol
 
When my PCV hose blew off during a trip, I was getting this popping racket when I let off the accelerator. You might look into the suggestions above regarding a lean-out condition before changing out the mufflers.
 
Just a little back-cackle. Although you may have some tune and mechanical issues aggravating the problem, A good pair of quieter mufflers and/or resonators should cure the problem. tmm
 
Spend money on good mufflers. End of story.
 
toolmanmike said:
Just a little back-cackle. Although you may have some tune and mechanical issues aggravating the problem, A good pair of quieter mufflers and/or resonators should cure the problem. tmm
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RustyRatRod said:
Spend money on good mufflers. End of story.
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You can try different mufflers all day, but if you have a leak letting fresh air into your exhaust system mufflers are not going to stop the popping in the pipes.
Only make it quieter, but if that's ok then fine.

Now the story can end. :D
 
TrailBeast said:
You can try different mufflers all day, but if you have a leak letting fresh air into your exhaust system mufflers are not going to stop the popping in the pipes.
Only make it quieter, but if that's ok then fine.

Now the story can end. :D
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Then fix that junk.
 
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