RX7 Muffler

L

Lynn77

New member
I will be attending a driver school this spring with a 1987 RX7 that has a Dynomax Ultra Flow muffler that I believe will not pass the 103dba sound requirement. Can I have suggestions on what will help reduce the sound or are there recommended mufflers that will offer performance but not exceed the noise requiremnent.
 
Put a bent tip on the end of the muffler and turn it AWAY from where the sound measuring equipment is located. This is worth a few db.

Drive well.
 
I have the same setup on my car with the full ISC Racing header, etc. The above suggestion is exactly right. Bent tip, down and away from the sound station. I register 99dB at both NHIS and Lime Rock.

AB

------------------
Andy Bettencourt
06 ITS RX-7
FlatOut Motorsports
New England Region #188967
www.flatout-motorsports.com
200_06_checkered.jpg
 
I check at 100dB most places with a straight through Dynomax and a straight tip. I'd guess a Flowmaster with it's baffling would have to be quieter. Add a bolt on turn down that you can rotate away from the sound check station at different tracks and you should be fine.

------------------
Chris Ludwig
08 ITS RX7 CenDiv
 
I'm not sure if this really works but it is thought provoking. Have any of you heard of this trick... I have headers in to a straight pipe with an Ultra Flow on the end (sans the downturn tip). The previous owner drilled opposing holes in the end of the muffler tip and ran a pretty heavy gauge wire thru, crimped at both ends to keep it in place. He swears that most of the loud IT7 cars in central Florida do this to save about 2db's.
 
Funny thing I never heard about that. It hit 98 dba every time out without that trick. I run a racing beat header, 2 2" pipes all the way back into a 3" collector and thru a dynomax with a straight tip on it. No problems and no over sound control. Just make sure your mounting bracket on your muffler will the exhaust pipe to grow in length. A solid mount at the muffler will put undo stress on the header and cause it to crack.

Now if someone knows about this wire trick in the muffler and it helps make more power, let me know.

Mike
 
Now Scott you can't keep going around telling all these old dog's new tricks. The way the wire in the exhaust is supposed to work is that for every wire(cut down coat hanger) you drop 1dB, so if you're close you can usually get away with a couple to drop the dB's without inhibiting exhaust flow.

Mike, i bet you wish you had known about that with your "daytona" exhaust a while back.

And for credibility, i got the trick from an old IMSA guy who happened to take my crew chief job.

Chris
 
Chris, it worked at Daytona just fine. Just because you could hear me from the pits while I was in Nascar 3 doesn't mean anything. I turned it away from sound control and it only registered 100. At Sebring I turned it the wrong (towards sound control) and I hit 109. all I could say to the Steward was "opps"
 
Ok I'll bite. What's the acoustic theory behind the coathanger wire trick?

Does it have to be in tension or just rattling around? If you put in 2 or more is that parallel or cross-pattern?

We need to be down several db this season so I'll try anything.
 
You must log in or register to reply here.
Back
Top