I have made the observation after hearing several vehicles myself and after reading MANY posts on this website, that virtually ALL the sound issues people are having with gas flow mods can all be linked to aftermarket cats. It seems that as long as you keep the stock cats, you can add almost anything else in terms of intake, plenum, headers, cat-back, and the sound will be acceptable. Switch out the cats, however, and even a simple cat-back can make the car too loud and/or unpleasant sounding. Anyone else care to comment on this?

 

I have RT cats and just ordered the APS exhaust. It's supposedly a very quiet exhaust as far as aftermarket exhausts are concerned. Hopefully it will be here before Saturday so I can have it installed. The salesman said he had it in stock (the shop is in Illinois) and that it will ship out today. I'll let you know then.

 

This is not true. I am running a Greddy EVO2 exhaust with Labree Resonated test pipes and the exhaust sound is ABSOLUTELY BEAUTIFUL. Not too loud by anymeans and just a very slight rasp, that is only there a fraction of the time. The exhaust sounds better than any clip I have heard on the boards and at highway speed has no droning and is barely noticeable untill you go to pass and it comes alive.

 

Glad to hear you have a combo that works well. I guess what I really meant was that *if* the sound is unacceptable, using stock cats will be more likely to solve the problem than changing anything else.

 

^^yep....I found this out the hard way I'm taking my testpipes off next week when me exhaust comes in...

I've searched the archives and read EVERY cat thread....I'd say about 80% of Z owners are NOT hapy with the sound their aftermarket cats/TP's make..(thats not including people who say the're happy, but are in denial )

IMO- just leave the cats stock if ur staying N/A...F/I seems to quiet the cats down alot tho..

 

You're right. I will get some clips of my exhaust when the weather warms up.

 

Yup, agreed. I've just done some extensive testing with two different exhausts (stock and Nismo) both with stock and high flow cats. Huge differences in sound. I'll do a separate post detailing my findings, but basically you are correct. High flow cats on most exhausts increases the volume dramatically over the stock cats. I can only imagine that test pipes (without resonators) would be even louder, although I never used test pipes.

 

Care to elaborate on F/I making for a more quiet exhaust sound? Thanks.

 

The turbos muffle the exhaust

 

Not necessarily FI, but specifically turbos. Since a lot of the exhaust energy goes into spinning the turbine, there is less energy post-turbo to create sound. This effect is not seen with superchargers.

 

Thanks for clearing that up, guys. Makes sense for turbos to reduce the exhaust noise a bit. I was just watching the 2 Z videos at aps's website, and even with test pipes the car didn't seem too loud. Sort of hard to tell with the dyno noise, but still...