None whatsoever, the stock exhaust really keeps the tone in check, makes the exhaust sound amazing, you'll have to hear it in person to get a good idea of the sound, but I get comments all the time about how good it sounds, people think I have a full aftermarket exhaust on it.

My only issue with the Berks are the hissing sound on the down rev. I am not sure if Stillen does this or not, but the reason I went with berks was for the gains. If I could choose again , I probably would have done F.I. resonated cats.

HFC's are definitely a good addition to the car. You'll see great gains without any obnoxiously loud/raspy exhaust noise. If you go with a full intake and exhaust system as well, you'll see outstanding gains. Shoot me a PM and I'll hook you up with a good price for AAM HFC's.

thanks, i wish i could hear it in person!

I just got back from having the Invidia Gemini and Berk HFC's installed. I would say it's not loud at all. I'm old and was worried about it being too obnoxious, but it really isn't. it seems loudest on the downshift blips. my previous car was a Lotus Elise with Forcedfed header, sport cat, Arqray muffler, and Fujita CAI. that was FAR louder than this car.

Boy them lotus's are very loud ! After that you could prolly tolerate anything.

How does the exhaust sound at idle and gentle acceleration? Sounds like at half to full throttle it's much better.

Quieter? Don't get HFC's.

i dont notice the sound change during regular driving but at start up and past 4000 rpm the sound change is obvious. when the car is cold the rasp is a little loud but once it warms up it sounds amazing. but the car feels way better under acceleration

If im at WOT i dont mind the loudness, its the everyday driving below 4K RPM that concerns me. I dont want to have rattles and drones... thats all
I just ordered a Berks HFC and Stillen G3 and CBE. I guess i`ll find out next week.
I guess the Fast. Int. CBE with 18" resonators and their Long Headers would have been perfect but louder...

anyone have a sound clip of a stock 370Z with hfc's?

i have the stillen G3 and berk HFC and there is no droan the engine has a very deep done with a lot of purpose if that makes sense. once it hits 4500 rpm it opens up

I have Berks waiting for me at the shop. It will be paired up with Nismo CBE. I have not heard any Berks with the stock exhaust. From what I remember the sound for Berks HFC is:

HFC w/stock exhaust = 4
HFC w/Nismo = 6
HFC w/Berk CBE = 8

Minicobra1' first post explains it all. Good write up. HFC's are the best bang for the buck!

Sound clip here:
http://www.the370z.com/intake-exhaus...on-x-pipe.html

I have had the Berk HFCs for six months and really like the mid-range growl under acceleration. You can feel the power increase and from what I have read the gains range from 15-20 hp (without a CBE). When you are cruising there really isn't much difference compared to stock. I do not hear any hiss at all from them. I added the Invidia Gemini's and really didn't like the increased volume and the low frequency sound (to me it sounded artificial). And it does drone at around 2000 rpms especially in 6th. Removed them and sold them to Bluestyle55 who really likes them but doesn't have the HFcs on yet.

Unfortunately I think this down-rev hiss is a characteristic of our engine. I noticed it subtly when my car was stock. It became more noticeable when I put the Stillen CBE on with stock cats. Now I've added HFCs and it's even more pronounced. The gains and overall sound enhancement are well worth the mods, but the hiss is unfortunate. I'll live with it.