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Good info here. I want to make a few changes to a 1990 C2 with Fabspeed RSR header/muffler package. I don't like the way the Fabspeed muffler sounds. Very American muscle-esque, Flowmaster/Magnaflow. I'd prefer something a bit more tuned if that makes sense. Was thinking about using a 997 center muffler like the below. Would be interested to hear any thoughts or suggestions and TIA.
I’ve installed a gt3 muffler to a 3.8l with race headers and cats. Vacuum valves are also installed and working correctly. I’m getting no difference in the sound level between quiet and free flow exhaust paths. Reading about 80db at idle at the tail pipe.
I’d like to get the exhaust noise down in the quiet flow setting. Any advice? I don’t think side mufflers will fit (964 engine in a G body).
I’ve installed a gt3 muffler to a 3.8l with race headers and cats. Vacuum valves are also installed and working correctly. I’m getting no difference in the sound level between quiet and free flow exhaust paths. Reading about 80db at idle at the tail pipe.
I’d like to get the exhaust noise down in the quiet flow setting. Any advice? I don’t think side mufflers will fit (964 engine in a G body).
On my GT3 the valves are on the side mufflers, not the center. So if you don't have side mufflers, I don't think there is a quiet or loud path on the center muffler. That's why when people replace the center muffler on a GT3 with a Sharkwerks delete, etc, the valves still work because the side mufflers are still present.
If you have no side mufflers, no valves, and a GT 3 center muffler the sound is loud if you go from the header directly to the lower inlet of the muffler. Top would be blocked off.
Quiet mode inlet is on top, bottom blocked off.
Very noticeable difference in noise between the two configurations.You need to drive and test, not just listening to idle.
With vacuum valves, same effect depending on valve position.
Fuel mixture very different between loud and quiet modes, which can be dealt with aftermarket ECU, like Motec M1
On my GT3 the valves are on the side mufflers, not the center. So if you don't have side mufflers, I don't think there is a quiet or loud path on the center muffler. That's why when people replace the center muffler on a GT3 with a Sharkwerks delete, etc, the valves still work because the side mufflers are still present.
pipes w/ valves to connect to the GT3 muffler directly to headers are available from Fabspeed and Soul, probably others as well
Thanks, its all connected and valves are working but there is no difference in noise level between top path and bottom path on the center muffler. I’m guessing, as others have said, noise suppression is mainly in the side mufflers which I’m not running.
There is a difference in the path taken via the GT3 rear muffler.
LOUD via the red route is basically straight through.
Quiet via the blue route is a longer path to lessen the noise.
AJD48, are you sure the valves are working properly because for what it’s worth my 964 is connected via the Loud path only with BBE heat exchangers mated directly to the muffler. It’s loud, 112 dB at idle.
Plus also has drone between 2400-2800 ish.
That’s helpful. Thanks. I spoke with MK Exhaust. I think they diagnosed the problem in about 30 seconds - very knowledgeable in this esoteric topic of GT3 exhausts on older 911s. For the quiet path, the exhaust tube must mate INSIDE the muffler with the quiet exhaust path. In my set up, the quiet path tube was just bolted on to the outside of the muffler body but did not extend inside to mate with the inner muffler tube. This resulted in the exhaust gas leaking into the loud path when it entered the muffler. I’ll modify the set up and report back. Hope this helps others looking to do this mod.
01-07-2018, 10:58 PM
