[BarryJB]

Originally Posted by Jaskas

I have been looking a quiter solution for my 3.6 as well... I have only the cat with tips. I love the sound, but wife and local track authorities dont.
Have you measured the sound level? Or have you compared the sound between the cat only, and with the silencers.
Your solution looks great but im afraid the noise level is still too high.

I hope to post a drive-by video clip this weekend (yeh, said that before and didn't get around to it, do have some stuff to edit down now), it does sound great, maybe it will give you some idea of the difference to how yours sounds. Got some more 2.25 pipe bits & bobs last week so may try to dummy up the longer tailpipes in a drivable configuration, get some more readings and driving time. It's really at idle that the low frequency pounding sound is worst and is what sets off the occasional alarm at just low barely open throttle rpm in town; it really seems the longer tailpipes are effective at reducing that and the droning effect mentioned before. We'll see!

It's definitely a work in progress - I'll check noise with a better meter, a Harbor Freight multimeter gave over 102dB at idle with the short stubs as in photo before I added the extra 6 inches, and a tad less after, but there was no definitive info on the type of measurement this was in meter booklet; but it is definitely WAY quieter than with just the cats (and no tips at all!) before we did this. For now my tests are mainly lots of driving around with windows open to assay DFF (drone fatigue factor) and note how often I set off the shock chirps on parked cars.

FWIW, CA DMV noise level spec for street use is not enforced (no funding or something like that) but is I believe 95dBA at 20 inches measured in an open non-reflective space (e.g., big field) at 3krpm.

I got down to high 90's and way less droning-type noises at idle and above just by Heath Robinson addition of more 2.25-in tailpipe (making about 20 inches each side) so if the dummy-up above works I'll have my guy make it real and see how that goes for a while - next will try the shortie Flowmaster HP-2's. Resonator tips may also make some small difference, if I can find any suitably shaped, short and matt-blackable.

No-one seems to like Supertrapps on these engines - a guy in Europe YouTubed a 3.6 cats-with-tips conversion with and without them - not impressive - BAA and as mentioned in above posts, they sap power well before they cut down noise enough. Some say the Car Chemistry style inserts (2.25 and up) work well in the tips for sound, others have tried the cone insert style there instead but homemade seems to be needed for 2.25 pipe as they're made to fit 2.5 and up. Latter reported as free-flowing, 1-2dB effect when used as intended in collector area... former reported to be overly restrictive... so it goes

Many say 1995 993 stock headers/cat combo is quite good; for me it's worth putting out some more time & $ to see if something can be done that retains the free-flowing advantages of that but keeps it livable and legal enough to use every day. Intend to get dyno before-&-after muffler/tailpipe install dyno numbers, once there's something seems worthy of such, and hoping results will avoid needing to proceed to any Plan B.