The Stovebolt Site Forums The Shop Area The HiPo Shop new exhaust question

Rebuilt the 350 in my '57 3/4 ton and had new exhaust done. The guy sold me on a pair of "Chrysler Hemi" mufflers. They are big and he said they would be quiet but not too restrictive. Dual with a crossover pipe and ended them just in front of the rear end (hydraulics for the dump bed make it a little challenging). They have a funny tinny sound out the tail but in the cab they seem to have developed a low frequency hum that resonates so bad, it's like a really bad toothache. Wondering if it's the mufflers or the fact that I didn't run the pipes all the way back? (He did say I can come back if I don't like them.)Any exhaust experts out there?

I run a set of flowmasters and dump mine just ahead of the rear axle. No wierd or annoying noises here.

Here's a sample -

http://smg.photobucket.com/albums/v228/Avette4me/video/?action=view&current=20091127173140.flv

http://smg.photobucket.com/albums/v228/Avette4me/video/?action=view&current=20091127173255.flv

Have mine the same as avetteforme and no problems with sound. i do have my cab floor insulated very well. ron

Cab is insulated with Dynamat, padding and carpet. Must be those weird mufflers.

Harmonic resonating? Might try to insulate the cab.

Put a set of mid-70's Cadillac mufflers on it. They're 2 1/2" diameter, inlet and outlet, and one muffler is sized to flow up to a 500 cubic inch engine. A set of duals with those pipes and mufflers will handle a 350 at any RPM you want to run with flow to spare. They're quiet, too!
Jerry

Change the mounting points on the mufflers, or add some.

You might need rubber hangers. Most muffler shops hook the system up with metal brackets directly or use plastic bushings.

With them exiting under the bed, you have turned the bed into a sounding board. The exhaust needs to exit past the rear axle out the side, or past the bumper to not resonate under the bed.

As for making a really quiet system, tie the two sides together into a 3" resonator, then use a 3" in, and dual 2.5" outlet muffler if you want dual exhaust tips, or a 3" in / 3" out if you want a single exhaust system.

Yes. Those last three posts resonate. I think you are going to be right about the hangers and the bed acting as a sounding board. It didn't do that before with short mufflers that exited out from the frame behind the cab. And they used rubber strap hangers instead of the more solid ones employed now. Once again, I should have talked to you guys BEFORE I pulled the trigger...doh!

Mine do that too with Dynomax Superturbo mufflers. They're quieter at idle but boom really bad at any kind of driving speed. My solution will be to switch to Flowmaster 50 series mufflers and insulate the heck out of the cab.

Went back and had him put on quiet mufflers like I asked for in the first place. Helped alot but I'm guessing that until I move the pipes aft of the rear end it's always going to resonate inside the cab at idle. I'm getting used to it. But then again, you can get used to hanging if you hang long enough...

Did you turn them down or do they run straight?