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      06-06-2014, 12:38 AM   #1
StickMon
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Varying exhaust note

OK, quiz me this:
I have stock headers, RE midpipes, stock X-pipe, and RE cans.
My exhaust note runs in 2 distinct modes, about 50/50 lately.
1) Lots of low growl, no rasp, but when I give it hard throttle I get this fairly loud hiss/buzz. Checked for leaks, checked for midpipes hitting the trans brace, even "de-buzzed" the heat shield on the rear reinforcement plate. No change.
2) Same growl, no hiss/buzz, but anything over 1/2 throttle results in this glorious intoxicating rasp. The good kind, like an F-Type.
And the blip shifts: explosive. It's like bacon, for your ears.

I think it might be temp related. Maybe the baffles in the X-pipe resonator or cans changing shape/tension.
It sorta correlates with what should raise the pipe temp.
More likely to get rasp mode when stuck in traffic at 4k rpm in first gear.
More likely to get buzz mode first thing in the morning or after long cruise at 80 mph in 6th.
But there have been enough exceptions to make me question that.

Data collection continues ...
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      06-07-2014, 07:48 PM   #2
pokeybritches
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Temperature plays a large role in the way the car sounds. When I first fire mine up, it's louder, has a deep drone, and there's more rasp (the bad kind). After it's warm, the car sounds perfect.
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      06-07-2014, 11:24 PM   #3
Finnegan
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You've covered all the bases. Hmmm. I'd guess something with the RE Mid-Pipe. I have Rogue cans, and no buzz. I'm not an acoustical engineer, but I had an idea that heat affects resonance frequency. And I looked up up, and my suspicion seems to be correct.

So either heating or cooling will change resonance. As you and Pokey noted, there's a correlation between heat causing activities and the sound. There's a calculator for the effects if anyone is interested.

You could try playing with modifying the resonance a bit....
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      06-08-2014, 12:21 AM   #4
StickMon
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Yea, I think it's the midpipes.
I was doing an oil change and general underneath inspection yesterday, and if you tap the midpipes, they ring like bells.
The wall material is very thin.
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