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Old 06-13-2006, 07:09 PM
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Interior resonance problems?

I have a 40 Ford with a dual exhaust system using spin tech mufflers. I am not sure if I have a resonance problem or a muffler reverberation problem. When I get to around 50 miles per hour, the interior cabin noise increases dramatically. If I speed up to around 60, the cabin quiets down again, but between 50-60 the noise is disturbing. I do not have any interior in the car right now, only insulation. However, even without upholstery, the car runs quiet under 50 and over 60. Could this be a exhaust leak causing this? What is the difference between resonance and reverberation? The exhaust system is 2.25". Any help on how to tackle this problem would be appreciated.

George

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Old 06-13-2006, 07:19 PM
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what size motor does it have
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Old 06-13-2006, 07:40 PM
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Its very common for performance exhausts to drone. Almost every one does it. Its just a place where undampened frequencies create a standing wave pattern inside the cabin like a subwoofer.

There are several ways to help. First of all, make the exhaust as long as possible; over the axle all the way to the back is quieter than just dumping in front of the axle. Don't use turndown tips, just let them exit straight or at a slight downward angle. Exhaust pulses can create standing waves between the floorpan and ground if they're pointed too far down.

Install some race bullet mufflers in addition to the spintechs. Use them like resonators and put them as far back as you can. That leaves the least amount of unbaffled tubing to generate resonances.

Your exhaust is exactly like a trumpet. You have something providing the vibes (the engine) and then the length and diameter of the tubing have large effects on what noise comes out the back. There are tons of other ways to help out drone, but a resonator is by far the most effective.
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Old 06-13-2006, 09:29 PM
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Try adding an H pipe, cheap and easy and it should help a lot.
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Old 06-13-2006, 09:38 PM
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i will go against the grain a bit and recommend peel and seal..it is a aluminum faced material used in roffing and if you stick some of this stuff in the doors and inside the body it quiets things down alot..changes and dampens the resonance.

Sam
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Old 06-13-2006, 09:40 PM
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Interior resonance problem

Quote:
Originally Posted by chevelless454
what size motor does it have
Chevelless, it is a 327.
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Old 06-13-2006, 09:44 PM
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Interior resonance problem

Quote:
Originally Posted by curtis73
Its very common for performance exhausts to drone. Almost every one does it. Its just a place where undampened frequencies create a standing wave pattern inside the cabin like a subwoofer.

There are several ways to help. First of all, make the exhaust as long as possible; over the axle all the way to the back is quieter than just dumping in front of the axle. Don't use turndown tips, just let them exit straight or at a slight downward angle. Exhaust pulses can create standing waves between the floorpan and ground if they're pointed too far down.

Install some race bullet mufflers in addition to the spintechs. Use them like resonators and put them as far back as you can. That leaves the least amount of unbaffled tubing to generate resonances.

Your exhaust is exactly like a trumpet. You have something providing the vibes (the engine) and then the length and diameter of the tubing have large effects on what noise comes out the back. There are tons of other ways to help out drone, but a resonator is by far the most effective.
Curtis, where could I locate race bullet mufflers? Does a place like Summit racing carry these? How far should the bullet mufflers or resonators be installed after the spintechs, or does it matter?
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