I have an hks downpipe, stock cat, and 30th anniv hi-power cat-back. It is noticeably louder than stock. One the freeway in 5th gear and 2500 rpm, it's like stock. At 3500, it's noticeably louder than stock. City driving about 2 steps louder than stock.

You can go here to get an idea of how the exhausts compare to each other.
http://www.norcalevo.net/forums/modu...view_album.php

 

The Apex N1 is a bit on the quiet side for an aftermarket exhaust, and it also happens to be one of the worst performing ones as well. Id say performance and noise level are roughly correlated.

A month back, Dave Buschur took a look at the N1, and noticed that the restrictor tapers all the way down to 2", which is worst than the stock exhaust. This may be the reason why it isn't that loud, but also why it doesn't perform particularly well.

 

no one has mentioned the RMR exhaust. Certified to CA 95db sound limit. (that's pretty quite)

 

The Milltek on my VW was the quietest system available. My car always made as much or more that other systems. Its not the sound but the design of the "box". There are many ways to do a muffler and a resonator, some flow better than others. One that tapers or chokes the flow is a bad design.

The milltek's resonator was very peculiar by having slots instead of baffles/holes to attenuate sound and was the key to the quietness and the high flow of the system.

 

I used to have RMR turbo-back and thought it was quiet but after hearing the AVO turbo-back I decided to switch since my kids keep complaining about the noise of the RMR system.
Anyway, they stopped that after I got the AVO so it should give you an idea. The AVO is very quiet like stock and only loud at WOT after about 4500 RPM with a very good performance loud. Sometimes, I wish it can be a little louder but I'm very happy with it. The only catch is it's on the expensive side at around $1250. Hope this help.

 

Nobody has mentioned the Vishnu Standard Turbo-back. It is nicely quiet (quieter than Vishnu Signature Series), and it is turbo back and comes with performance cat. It is sort of expensive, but it comes with the cat and you wont need to purchase a separate down pipe, so its not really any more $$ in the long run.

CPT Evo

 

I've heard that the Thermal R&D is very quiet. It is a full stainless, 3" exhaust with an oval muffler(similiar to stock design). I believe that exhaust system also tapers at the cat.

 

I have Thermal R&D and the sound is just like stock. Its a little louder but I have a Downpipe, and a Highflow cat. Thats the exhaust I would go with if you want good quality and performance.

 

The Fujitsubo is REAL quiet, I almost thought it was STOCK.

 

I have driven a car with the Vishnu standard and did not even notice it had a exhaust on it. It is very quite. Maybe a tiny bit louder then stock.

Also fit and finsh is awsome.

 

Can anybody post somesound clips?

 

I should be getting my Fujitsubo RM01A by the end of the week. Hope it's as quiet as I think it is. I sold my TurboXS catback after 2 hours of use because it was way too loud for me. Sounded great though.

 

wow look at the Fujitsubo RM01 exhaust.... so many sharp bends.... thats why its quiet but ur making less power

 

look for a jasma approved system. these have noise restrictions imposed for use in japan...blitz realise TT system is a good one

 

AMS exhaust is quiet when cruising. A little louder at idle and when you get on it but overall it is a quiet exhaust.