High flow cats

[Billsgx]

Are high flow cats worth the price for what you get? I see Stillen's are $493.00.
Also, I see it says on their site "offroad use only". I already have theStillen cat back installed.
Should I just check with my local shop to see if they are legal and state inspectable?

[joe603]

If you have an emissions test, they are "illegal" and may fail...but a spot inspection should be fine, since you still have a CAT.

[arrow23]

I installed the Stillen High Flow Cats on my 2008 G37S Coupe back in June.
I installed them myself. The passenger side was not too bad, but one of the bolts on the drivers side is very hard to get to, as the steering shaft is in the way.
I am very happy with the fit, sound, and could feel the added HP.
I now have the ARK Grip Cat Back Exhaust on and love the set up.
I think the Stillen HFC's are definitely worth it.

[Billsgx]

I'm just worried about state inspection time.
How much louder are they?
Any ballpark idea of the power gain?
Probably not unless dynoed I'm assuming.

[arrow23]

According to Stillen's Dyno charts on their web site, they add about 15 HP.
I would think you definitely would have to get a tune to achieve this kind of gain.
As far as noise, they are really not much noisier, especially during normal driving.
When you floor it, then they are a bit louder.

[audtatious]

Hi-Flows are usually "49-state compliant" in that all states are fine with them except CA. They do conform to Fed Emissions use.

You should validate with your state laws.