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  #16 (permalink)  
Old 05-04-2009, 03:34 PM
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Quote:
Originally Posted by h0trod389
im running a 389 in my 68 tempest, super comp headers, stainless 3" exhaust with delta 40's and a x pipe.

when im cruzing, and let off the accelerator, it will idle down and will emit a low but distinct "boom".

when i smash the throttle, she runs like a bat outta hell.

sometimes when cruzing on the freeway it will make other people look.

i tried to solve this problem by isolating plug wires, changing timing and even rejetting my carb...

nothing worked, it has a pretty radical cam in it ( 290 dur @ 050, with .525 lift 112 centers).

since it didnt hurt peformance, ive learned to live with it.
I wonder if in your case that could be an (after fire).. unburned fuel collecting and igniting in the muffler?

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  #17 (permalink)  
Old 05-04-2009, 03:39 PM
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my "booms" are constant when cruising just off idle
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  #18 (permalink)  
Old 05-04-2009, 05:04 PM
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Quote:
Originally Posted by weirdbeard
I wonder if in your case that could be an (after fire).. unburned fuel collecting and igniting in the muffler?
could be. but like i said, it didnt hurt anything so i never went any further.
only happens while cruizin without throttle. and at 700-1000 rpms.
anything above that, she growls.
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Old 05-05-2009, 07:38 AM
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mine does the same thing... but its not a sonic boom... i have 350 with headers to about 2-3 feet of pipe to purple hornies. i cant hear myself think. but thats what i wanted.
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Old 05-05-2009, 02:12 PM
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its like a random muffled boom other than the exhaust sound. it is coming from the mufflers though.
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  #21 (permalink)  
Old 05-05-2009, 08:22 PM
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Sounds like fuel lighting off in the mufflers

Shane
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  #22 (permalink)  
Old 05-05-2009, 08:57 PM
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Exhaust backfires can be caused by several things, but I would check exhaust valves first. They might be sticking open/not sealing well. I would also check the timing chain. Usually they start making a lot of noise before they affect the valve timing too much, but if there is a lot of slack it can cause backfiring. Excessively rich mixtures can make backfiring, but you would probably notice black smoke.
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Old 05-06-2009, 04:03 AM
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i am running a gear drive. i dont think it is a backfire. doesnt sound like an explosion at all.
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Old 03-17-2010, 10:20 AM
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any other ideas?
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Old 03-17-2010, 10:30 AM
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as already stated its probably your exhaust system. Its the most likely culprit based on what you've stated. Start there.
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Old 03-17-2010, 10:34 AM
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Resonance is wierd knew a guy once with a mid 70s chevy truck and at a certain rpm you couldn't even hear yourself talk let alone anything else
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