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July 18, 2006
Mufflers
Installing the NASCAR take-off boom tube side exhaust (previous exhaust was the SLP 3" catback with a single 3" in dual 2.5" out straight through exhaust, they claim is good for 650hp), the Z28tt sounds great at the track. It is a bit loud, and I'd like to keep my neighbor happy, so now I'm on the quest for a decent pair of mufflers. Searching the net, here are some opinions I've found at:
www.gnttype.org
www.turbomustangs.com,
Muffler shootout - http://racetruck.tripod.com/muffler.html
http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm
Another muffler test - http://www.v6z24.com/howto/mufflerchoice
Part of the noise could also be the open wastegate dump pipes - I may have to look into bringing them into the downpipes as soon as I up the size from the small 2.5" dual downpipes currently on the Z28tt.
I called Dynomax, and according to them, the bullet race mufflers lower the dB by 2-4, while the Ultraflow Welded and Ultraflow SS lower it from 10-12 on the short ones and 12-17dB on the 20" long mufflers. Since muffling depends on the length, dual 3" exhaust with their own mufflers will be quieter than a single 4" exhaust. I followed up by browsing through their catalog. Their 3" in/out Ultra Flow Welded Universal Mufflers all flow 1800 cfm @ 20.3" of water for the straight through (center-center or left-left inlet-outlet) mufflers, which they estimate is good for 818 loss-free horsepower. Changing to a center-left knocks it down to 1300cfm/591hp and a left-right gets it to 1100/500. Their 3-1/2" center muffler is good for 2200 cfm/1000 hp, but I wonder how well it muffles. These are all 4-1/2" x 9-3/4" oval mufflers.
Spoke to Magnaflow, and the tech recommended their 12469 5x8" ovalized 3" dual x-pipe muffler, that's 18" long, which has a roughly 6" cross section in the middle of the x-pipe (http://www.magnaflow.com/02product/shopexd.asp?zone=main&id=476). I wasn't able to get any flow numbers or estimates of how well it quiets things down. They also have 4x9" oval mufflers for more ground clearance, and a 5x11" (pn 12599) dual in/out oval as well.
After reading dozens of threads this morning, speaking to tech support, and thinking things over, it seems like the choices are narrowed down to the Dynomax Ultra Flow, Magnaflow Universal, or Hooker Max Flow. Time to measure under the car to see what needs to fit.
Bullet type mufflers - flow great, but barely muffle
Borla XS - quiet from the tests, but no 3" or larger...
Flowmaster - Terrible flow
Hooker Aerochamber - quietest, higher backpressure
Dynomax Ultraflow - straight through, decent quieting
DNA - Direct Natural Airflow - Race muffler - loud, flows great
Magnaflow - great flowing, quiet, very low backpressure (http://www.turbomustangs.com/smf/index.php?topic=63459)
Hooker Max Flo - quiet at idle, loud at WOT.
Posted by Z28tt at July 18, 2006 1:56 PM