Strange vibration/firewall noise on deceleration with SPD catted downpipes

[pelotonracer2]

I recently had SPD catted downpipes installed. Coasting or deceleration it "sounds" like there is something rubbing or touching the firewall and there is a spongy feel to the steering wheel when I press the acceleration pedal. I'm wondering if maybe they didn't tighten something up OR there's a loose or broken motor mount. Anyone else have this issue after SPD downpipe installation? When engine is revving, the exhaust system (mid pipes) are moving around a lot, but the installer can't see anywhere where it would be touching. Any help or advice would be greatly appreciated. I don't think I can just live with it this way as the rattling, vibration noise is unaceptable.

EDIT: Nevermind, admins please delete

 

[TMac]

You are simply getting increased vibration from the install. As far as your "installer can't see anywhere where it would be touching"- it doesn't have to be touching. The very fact that they are vibrating will generate sound. Ever see a tuning fork?

That vibration is affecting the firewall like a drum, and probably transferring that energy into the steering wheel, because obviously downpipes have nothing to do with a "spongy feel" in the steering wheel.

What type of isolation (flexpipe) is used after the downpipes? Do you have different midpipes? Did the installer use some sort of flexible hangers on the midpipes?

 

[pelotonracer2]

You are simply getting increased vibration from the install. As far as your "installer can't see anywhere where it would be touching"- it doesn't have to be touching. The very fact that they are vibrating will generate sound. Ever see a tuning fork?

That vibration is affecting the firewall like a drum, and probably transferring that energy into the steering wheel, because obviously downpipes have nothing to do with a "spongy feel" in the steering wheel.

What type of isolation (flexpipe) is used after the downpipes? Do you have different midpipes? Did the installer use some sort of flexible hangers on the midpipes?

I'm using the factory accordian crap

I ordered 2.5" Lethal Performance mid pipes with the weave style flex joints. I hope this tones it down. I have a custom 2.5" exhaust system.

I am aware of the factory flex pipe issue. I thought about getting better, firmer hanger grommets. The factory ones are very soft.

The steering wheel issue only occurs coming off idle upon throttle tip in, like leaving a stop light.

 

[TMac]

It comes down to frequency and resonance which I can't even begin to calculate.

I ordered 2.5" Lethal Performance mid pipes with the weave style flex joints. I hope this tones it down. I have a custom 2.5" exhaust system.

The flex joints are probably a good start for dampening.

I am aware of the factory flex pipe issue. I thought about getting better, firmer hanger grommets. The factory ones are very soft.

Not sure about that- a harder grommet/hanger will tend to raise the frequency which may be a good thing at least as far as the firewall is concerned. I'd leave that as the last thing to experiment with.

The steering wheel issue only occurs coming off idle upon throttle tip in, like leaving a stop light.

Once again, a resonance issue off the firewall- it'll magnify certain frequencies based on the proximity and large surface area. I'm assuming it is at lower RPMs which probably has more to do with your custom exhaust than anything else. The stock downpipes have more dampening built in to the surrounds, so you might have to live with a bit more vibration.

 

[pelotonracer2]

Just an update:

Bought 2.5" midpipes with weave style joints and had the muffler shop add two new hangers and no more vibration. Sure sounds good though.