Eliminating Exhaust Resonance?

[Jelly]

When I got my ‘ol truck, it simply didn’t have an exhaust system on it…the two pipes joined together aft of the engine (if in drivers seat, left side exhaust pipe crosses over and connects to the right side pipe to form one 2.5” pipe) and that was it...no converter, muffler, etc...pretty darn LOUD!

Anyways, so I wouldn’t go deaf, I simply got a pipe from the local muffler shop, a cheap muffler from a parts store, a little turn down pipe, and some cheap hanging material. The exhaust, although this is a ½ pickup, is set-up like any medium duty truck…simply exists underbody right in front of the rear axle.

Anyways, the sound is muffled down a GREAT deal now, but when you let off the throttle (my truck has a 5-spd. stick), you get a bunch of resonance in the cab that is very annoying!

How does one go about eliminating this resonance?

[ July 12, 2004, 02:14 AM: Message edited by: Jelly ]

 

[rpn453]

Maybe you need a resonator. They're kind of like a second muffler, and I believe they get rid of those low frequencies that come into the interior. They're a straight-flow item and I don't think they hurt exhaust flow at all. My dad took a cat off a Sunbird a few years back and the muffler shop guy recommended he put a resonator (at about $40 cdn) in its place, since the cat also reduces exhaust noise. He decided to try running without it, but went back the next day for it! Since then, we've always put resonators in place of the cat when doing exhaust work.

 

[Steve S]

Get a good muffler and an over the axle pipe .

 

[rpn453]

quote:

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Originally posted by Steve S:
Get a good muffler and an over the axle pipe .

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I guess that would be the first thing to do.

I must have missed that part of the post the first read through.

 

[TheTanSedan]

You don't necessarily need a resonator. Ford is not the only manufacturer in searches I have done who once recommended clamping weights to the tailpipe past the axle hangers. I'd try some angle iron there, and just ahead of the rear axle; moving them around to get the problem solved.

Also, do you have rubber-isolated hangers? Many cheap installations I have seen have but a small donut screwed onto the frame where a piece of strap is used to hold the pipe. Not ideal, as there is next-to-no isolation.

NAPA has a good selection, I'd look for ones that have both frame-mounted rubber along with a piece or two suspending the pipe.

Take a look at a few late model cars, exhaust and muffler manufacturer catalogs first.

No reason to increase the backpressure if it isn't needed.

On the other hand, this company seems to have a good rep for resonators that will last:

http://www.stainlessworks.net/Mufflers.htm

(I realize that a "cheap" system is what is needed oftentimes to get started, but I've heard and read good things about these behind "loud" mufflers where the driver wanted some peace on long trips).

I've long thought that a pair of these, behind the chambered mufflers of your choice [mine would be HOOKER AeroChamber], would be ideal. Last about indefinitely with a mandrel-bent system of aluminized steel.