which one is best aftermarket exhaust?

FPenvy

test pipes really are the way to go for sound and better yet power.

most HP gains are with either test pipes/headers or long tube headers.

to get to my sound you need to be ok with being very loud and having in cabin drone. there's ways to dial it down with resonators and some dynamat in the car/trunk area. personally I enjoy it as loud and just nonsense volume that it is lol.

to solve your problem with not wanting test pipes your best bet would be to either start with AAM short tails and see if that gets you anywhere where you want to be.

although that'll be loud may not be the volume you want exactly.

kinda hard to pull off since not many CBE's come with a no muffler option nor do many short tails match up to anything but the stock exhaust.

soooo you're in a tough spot if you want big volume and stock cats.

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324whp/258wtq AAM Tuned |F.I. NonRes CF CBE/NonRes TestPipes #373|UpRev Tuner|Akuma Motorsports Intakes|Z1 34 Row Oil Cooler