Black91Z28

hey,
I have hooker headers, no cat, 3" piping, and a flowmaster 80 on my car. For some reason when i get to a certain RPM's it sounds like a redneck truck but then stops again....and sounds great thereafter.....does anyone know what causes this cackle? is it because i have no cat? do i need a glasspack or something? any help is appreciated!

thanks

Bristol

I have the same basic set up but with Edelbrock headers and I get the crackle your talking about only on deceleration. I think its cause of the loss in back pressure cause with my cat the noise doesnt occur

Black91Z28

ya, its like I accelerate normal and it doesnt do it, but when I give it about 1/2 throttle or more, it cackles for about 2 seconds, then goes back to sounding good again, and I cant understand it because a ton of people (including some of my friends) have the same setup i.e headers, 3" exhaust, no cat and muffler, and I dont hear it in theirs nor do they complain about it....I must be nutso or something

Fast-Formula

I had the same noise on a 84 TA I use to own,same headers,exhaust,muffler and it turned out being the tin heat shield that runs under the rear of the car between the back of the gas tank and the body right above the muffler.at certain rpm's it would
vibrate and make the same noise you described.Just something you can check out.
Thanks Bill

Black91Z28

I checked out the heat shield and all the bolts are tight, what did you do to yours formula?? or did you just leave it alone....I dont know if its just the wrong amount of backpressure, but its got me baffled and I, nor any of my friends, can figure it out.....

marek85

You might wanna check the heat sheilds above the axel where the pipe goes over it. My Camaro rattles there and its really bad. it does the same thing that you describes.

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Rob
1985 Camaro
305 4bbl
IROC Rims
1970 Chevelle SS
396 factory Bore 402
All Numbers Match.

Black91Z28

I dont think thats the problem, I checked those two things and the bolts on them are tight.

Rumblin91

It's the muffler...all flowmasters that I've heard cackle. I have a 40 series and it cackles bad.

firechicken_3

its not that the screws/bolts are loose, its physics, everything has a "resonant frequency", when that frequency is obtained, it causes the item to vibrate, in this case, when you hit a certain rpm with a certain loud, it is hitting the resonant frequency of the heat shields,

well what do you know i remembered something from physics, but i could still be wrong, just my thought

Fast-Formula

firechicken is correct.I don't know if you could attach any sound deddening material
to the heat shield or if it would last melt, fall off etc.

Black91Z28

Thanks for the input guys! For some reason, it sounds better now after almost a week of driving it. Is there a break in period on flowmaster mufflers? I heard something like that

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1991 z28
350 Tpi
Hooker headers, flowmaster 80, custom ram-air

marek85

Now that you mension that I beleve that there is a 3000 mile break-in period

------------------
Rob
1985 Camaro
305 4bbl
IROC Rims
1970 Chevelle SS
396 factory Bore 402
All Numbers Match.