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Topic Review (Newest First)
03-17-2010 10:34 AM
BBCMudbogger 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
03-17-2010 10:30 AM
ap72 as already stated its probably your exhaust system. Its the most likely culprit based on what you've stated. Start there.
03-17-2010 10:20 AM
brian400ex any other ideas?
05-06-2009 04:03 AM
brian400ex i am running a gear drive. i dont think it is a backfire. doesnt sound like an explosion at all.
05-05-2009 08:57 PM
curtis73 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.
05-05-2009 08:22 PM
Chevrolet4x4s Sounds like fuel lighting off in the mufflers

Shane
05-05-2009 02:12 PM
brian400ex its like a random muffled boom other than the exhaust sound. it is coming from the mufflers though.
05-05-2009 07:38 AM
83SILVRADO 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.
05-04-2009 05:04 PM
h0trod389
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.
05-04-2009 03:39 PM
brian400ex my "booms" are constant when cruising just off idle
05-04-2009 03:34 PM
weirdbeard
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?
05-04-2009 12:02 PM
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.
05-04-2009 10:29 AM
brian400ex any other ideas? you hear the usual exhaust tone and then you hear a lil "pop" mixed in there. sounds like sonic booms. kind of muffled. not a high pitch sound.
04-27-2009 11:01 PM
curtis73 You're describing what is typically referred to as exhaust drone. It is very common with 40-series. Depending on how your exhaust is configured, there is always risk of drone, but you can mostly eliminate it with quieter/better designed mufflers.

The drone comes from the exhaust creating sounds that resonate inside the cabin much like subs resonate best at a certain frequency in their box's volume.

The phenomenon is known as a "standing wave" where the length of the frequency bounces back on itself in a mirror image. You can duplicate the same thing in the shower by singing. Start sliding up in pitch and you'll get to a frequency that makes it sound like the shower walls just collapsed on your ears.
04-27-2009 06:05 PM
Torque454 ONE of the 350s (notice i said one, meaning there were several engines in it at one point) i had in my old 72 pickup started doing that after it got hot on a highway trip once. The next time i took it out on the highway it blew up. Not sure what the sounds were caused by but it was related to it getting hot. It never ran right again after that. I hope this isnt the case for you but its possible. I suspect it was a valve problem.
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