Ear vibrating resonance

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Robj

Robj

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I've been looking at new mufflers and it's very difficult to know how it will sound in the car. Smittysduster started another thread on mufflers and like he says all the websites seem to say something different and listening to a set of mufflers on youtube doesn't help me.

Idle is not too loud and sounds great and even listening to the car drive by at varying speeds, it's not too loud at all.

Where I have a problem is driving inside the car from about 40 mph to just over 50 in third gear. The resonance at that rpm range can be almost unbearable to the ears if you just cruise at that speed or are climbing a slight hill. Above 50 mph it mellows right down and you barely hear the exhaust at all. At 70 it's a beautiful purr in the background with normal conversation entirely possible.

318- Hooker headers- 2.5 pipes- narrow H pipe- 14" turbo mufflers- pipes up and over the axle with stock type turn-downs.

Some sites seem to indicate that a 3 chambered muffler would be the ticket and others seem to say a turbo should be fine. I'm not sure if I need longer turbo mufflers, chambered mufflers, resonators in the pipes up on either side of the gas tank or what.

Like I said the volume isn't the problem it's that resonance that gets in my head.
 
There is a resonance between the two mufflers in a specific rpm range. I had the same problem with a 2.5" cat back Super Turbo muffler system that I installed on my 1990 Mustang GT. It resonated at 1700 rpm which is cruise rpm in 5th at around 70 mph. Turned out with the stock system one muffler was a little longer than the other to prevent the resonance.

Installing a small resonator in front of one of the mufflers should move the resonance frequency as well as reduce it. The question is to what rpm it will it move it and by how much? That I do not know.
 
Could also try changing the H-pipe's location, 5 to 10" closer or further from the collectors. I throw that out here, recognizing that could be a royal pain/expensive experiment for some and easy and cheap for others.

With a program like Pipemax, you can estimate where the best and worst locations are for power and torque. I'm sure there is a relationship with how it sounds, but pipemx doesn't address sound. My guess is that selecting the best for power might shift the resonance to the upper rpm range.
 
I had an eerily similar drone/resonance in a past car of mine. Talked to the Flowmaster guy at SEMA that year and he said that my head-pipe to tail pipe lengths ratio was wrong and for me to try clamping a heavy hunk of something to the tail pipe at it's 1/2way point. I cut off a hunk of lead and hose clamped it on. The resonance went away. Apparently the weight makes the pipe, acoustically, two pipes, that in my placement, were each 1/2 as long as original.

FWIW 302/5.0's are NOTORIOUS for resonance in that 1700-1800 rpm range.
 
buck351 said:
I had the same problem with drone. Tried different mufflers even the dynomax VT which is suppose to get rid of drone. It reduced it but it was still there just at a lower level. I finally eliminated it with branch resonators. Here's the thread on my drone journey. http://www.forabodiesonly.com/mopar/showthread.php?t=202506
Click to expand...
I'll switch to the other thread for discussion so that it all stays together for others.
 
ntsqd said:
I had an eerily similar drone/resonance in a past car of mine. Talked to the Flowmaster guy at SEMA that year and he said that my head-pipe to tail pipe lengths ratio was wrong and for me to try clamping a heavy hunk of something to the tail pipe at it's 1/2way point. I cut off a hunk of lead and hose clamped it on. The resonance went away. Apparently the weight makes the pipe, acoustically, two pipes, that in my placement, were each 1/2 as long as original.

FWIW 302/5.0's are NOTORIOUS for resonance in that 1700-1800 rpm range.
Click to expand...

Was that to just one of the pipes or to both pipes?
 
The system (on a Ford 302 btw) was a pair of 2.00's merged to a single 3" with a single Flowmaster just in front of the rear axle. The head pipe length was really short compared the tail pipe length, so the chunk of lead went on the tail pipe just behind the rear axle.
 
Everything has a resonance point. Slap down some sound deadening material from lowes and call it a day.
 
PoisonDart74 said:
Everything has a resonance point. Slap down some sound deadening material from lowes and call it a day.
Click to expand...
Why not try killing it at the source instead of adding more weight?
Robj said:
Hey Buck- Looks like I'm in your neighborhood as far as the hertz go. About 125Hz. Would you mind sharing your pipe length and saving me the math??? Heh heh...

View attachment 1714713038
Click to expand...

Vibes analysis phone app? An MSME friend of mine used one to diagnose why his rear drive-shafts fail so fast.
 
ntsqd said:
Why not try killing it at the source instead of adding more weight?
Click to expand...

Some of the fanciest cars in the world use tuned traps in the exhaust. No, don't ask me to post examples. I've seen 'em. I'm to dammed old and mean to go search em out again.
 
They also use weights at various places both on the drive-train and on the exhaust. It worked for me, took maybe an hour total.
 
That sound deadened is feather light, inexpensive too. Only need 30% of panel done.
 
I tried strapping some steel weight to the tail pipes and it didn't make any differance. The branch resonators did. They were more work but it worked.
 
It matters where you put the weight on, not just that you did.
 
Bzzzzzzzzzzzzzzzzzzzzzzzzmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm.
 
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