How to get rid of interior resonance?
 

I have 3" mandrel bent exhaust with x-pipe, and 2.5" dynomax ultraflow mufflers. It had 2.5" mandrel tailpipes. I thought the straight through design of the ultraflow mufflers with not have the interior resonance that it does have. It resonated pretty good at about 1500-2000 rpm. Is there any way to make it not do that?

I had the same problem with the full 2.5" system on my 455 equipped GP and had to add resonators into the tailpipes. I used long straight-thru tubular "cherry bomb" type muffs with 2.5" cores. I raced the car before and after the mod and didn't see any difference in performance.

Les

exhaust too big for velocity, laminar flow problem.

Yep thats gotta be it!

I don't think that's it engineer. I had a 400-425 horsepower 400 with the exact system, and it had exactly the same drone. Now I have a 600 horse 461. Same same.

It is just a characteristic of the exhaust sytem. I hate to add more mufflers, not for performance reasons, I just don't want to crowd things up anymore under the car.

Any other way? Anybody know if Magnaflow mufflers have that drone?

I don't know that this would help you, but it's one way to alter the acoustics of a system without adding components. Replace some section of the tailpipes with bendable tubing. Not flex-tubing, but the convoluted bendable type. I used it for over-the-axle tailpipe sections on a Ranchero, and it made a big difference in the sound.
By the way, it's barely bendable- you darn near need a pipe bender.

Or, add mass to the system. Most late-model vehicles have some type of bracket or lead-filled weight clamped to the exhaust, or bolted to a flange. Yes, you're adding weight. True, you're putting more stuff under the car. But- it will cut down on the resonance (or, push it into a much more liveable RPM range)...

I had heard that before about putting a weight on the exhaust or something. Where do you put it? On the mufflers? I may try that if I could figure out a way to trail and error it until I get it the best.

Think of the exhaust system as a large tuning fork and you wish to change the frequency. The resonators that I added probably altered the "tune" with their mass as opposed to muffling the exhaust, since you can throw a hardball straight thru them :eek: .

Les

I have turndown tips in the back too. I wonder if I put a 24" section of the corrugated stuff on each side behind the rear end, if that would make it resonate less. That would rule.

I guess I could tuck a pair of resonators up in there too. I have my tailpipes tucked up in that cavity between the quater panel and the frame rail. from the side of the car, you can't see that I have tailpipes.

Wheelspin, did that make your car alot quieter? I don't really want to change the sound, just stop the resonance. What about the dynomax sonic turbo mufflers? resonance?

Gearbanger,

The addition of the two resonators (2.5" cores), located in the tailpipes on each side of the fuel tank, totally eliminated the resonance. The GP ran 14.45/ 96 mph @ an adjusted 6,000 ft. weighing 4450lbs. WITH the resonators installed.

Les

I doubt that anyone can answer that. Even factories use a lot of trial-and-error when designing exhaust systems. Convoluted tubing is an acoustics-altering component, but you'd need to try it.
I think that adding resonators behind the axle has the best chance of success.

Cool, I'll probably try one or the other sometime soon.

Thanks!

Any other way? Anybody know if Magnaflow mufflers have that drone?
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Mine don't.With X-pipe,Great sound, I think they are the best money can buy at this time. Flowmasters are now "old school" technology.IMo

I have Magnaflows [ stainless steel ] & they don't drone. Having worked on many cars for decades, different brands & body types, I think it is just about impossible to predict what the exhaust system will sound like, & whether resonance will be present. Just changing an intake manifold from a dual plane to a single plane can change the exhaust sound, and cause 'drone' that wasn't there prieviously. It's a trial & error deal.

Magnaflow's are a great product.

I have the same problem with my 73 Grand Am. It has a 400 motor, ram air manifolds and a 2.5" mandrel bent exhaust using Walker Dyno Max Hemi style mufflers (the ones that Jim Hand has tested). The drone between 1600 and 2100 RPM (under load) is almost deafening! At any other RPM the exhaust is nearly silent though.

I can't decide if I will change mufflers, add resonators or try Car Chemistry Exhaust Inserts. It seems that when I searched this forum before that a couple of guys tried the inserts and were happy with the results. I called the company and was told that they will help to eliminate the resonance. I am leaning towards the inserts, placing them just downstream of the head pipe.

Here is a link to Car Chemistry's web site.

http://www.carchemistry.com/ccinserts.html

Pittsburg64........ I am assuming you mean turned down tail pipe. Yes, I have them. My exhaust also has a tinny sound to it, especially right off idle under load.

I forgot to mention that I have an X-pipe (crossover) ahead of the mufflers. How about your system? Do you have any droning/resonance in your exhaust?

Looking at the inserts on the Carchemistry site, it seems all they do is convert a section of your exhaust pipes into baffle type mufflers. You control the muffler's backpressure by the # of discs added. The tests they showed comparing 2 & 3 disc inserts shows the 3 disc losing hp, which probably indicates more discs increase restriction. The fact that the comparison between open pipes & the inserts showed a power increase with the inserts could be because the open pipes were sized too big for the engine & the inserts merely corrected the sizing problem. I would like to see a comparison where the different OD open pipes were FIRST used to optimise hp, & THEN add the inserts. They may reduce hp then.

I just put in a new exhaust for my car. 3,5" headpipes 3" Ultraflows, 3" tailpipes, 2,5" Ultraflow Bullets before the bumper. Wow what a difference with the old system (3" headpipes 2,5 Ulttraflows, 2,5 tailpipes), much more quiet, it almost sounds stock, which it is far from, 7.0 sec in the 1/8th first time out ever.
The bullets make all the difference, just look at the high end Euro cars with 600 plus HP, the all have multiple mufflers in place, still make good HP and are whisper quiet.