there are two cats; one per header

in most exhaust layouts, the catalic converters are where a lot of back-pressure builds up due to the setup, hfcs free up that pressure and allow for a briskier throttle response, though often at the expense of some high-end power (loss of back-pressure in high rpms tends to lose hp, tho i'm not sure if thats the case with the Z)

High-flow cats give the most gains of all the bolt-ons.

It's not the case:

Run Details

Generally, without raming more air in, a less restrictive exhaust will often lose some low end power while picking up some high end power -- this is because optimal cylinder filling tends to happen higher in the rev range, at which point, smaller diameter piping or cats may be somewhat of a restriction.

However, at low speed, when there is less cylinder filling, those "restrictions" are closer to approximating optimal exhaust flow under those running conditions.

So... in short, extra exhaust flow is only helpful when/if you are sucking in enough air to take advantge of it.

In real life, you end up with some sort of compromise, and then tune around that.

yea sry for not being clear, thats what i was trying to get at.

from my experience on the G, most exhausts actually sacrificed some top end for more mid-range power. After I installed my fujitsubo legalis-r, i noticed there was a 2-3 hp drop at redline, but mid-range power was improved. I only had a z-tube and k&n drop in on that car to help with air intake

TP's, stock resonators, and muffler delete...let you know next week, but stock Nismo is weak...even with TP's...

you could notice a 2-3hp drop with your butt dyno? wow! sensitive equipment.

I wonder how it got that sensitive?! LOL!! :bowrofl: :bowrofl: :wtf2: Been drinking a few cold one's I couldn't resist!

I know the nismo isnt much louder than stock, but does the tone of the sound change inside the car? i like the stock sound a lot, but i love the sound of the nismo much more. If i got a nismo exhaust would the tone change be noticeable inside at all?

IMO, no, not really. A tad deeper and volume, but really not noticeable...that's why I took my rear section off... :D

I dunno mine is sounding pretty beast inside right now, very deep tone at mid to low rpms...im kinda liking it, just with it were a bit louder and more responsive. So so HFC's with my stock setup wont be too loud, and wont throw any codes? Thats my main concern holding me back...

I have the nismo exhuast with Berks HFC's now. It did not change the sound that much. It is just a little louder, but not a night and day difference by any means. I have never had any codes (CEL) or any problems. I highly recommend the hfc's. I just ordered longtube headers so my cats will be for sale as soon as they come in. $300.00 and they have less than 1,000 miles on them. :tup:

Hold them for me, I'll buy them when you get your headers on! Also, how much of a power difference did you feel with the HFC's?

With TP's at least, you will feel more of high mid to high range pull...

Thats cool, long as i can get a lil more deep throaty sound and enough power to feel a slight difference ill be happy. Im sure HFC's will provide slightly noticable increase throttle response as well. So the Berks HFC's are direct bolt on replacement?