[ParisTNDude]

Originally Posted by DGthe3

Alternatively, it could be that the 455 that they've been advertising is with the performance exhaust & it might be 450 (or so) without.

But really, does it actually matter? If there is any gains, its going to be roughly 5 hp. Thats not going to do anything to appreciably change the performance of the SS. It might make people feel better to quote a higher hp number ... but a 1% difference isn't going to have any real effect on how quick the car is.

The LS3 engines in C6 Corvettes were rated at 430 HP and increased to 436 HP with the addition of the NPP exhaust.

Most of us spend a lot of money on axle back exhaust systems where the manufacturer claims as much as a 15 HP increase, but I doubt anyone could prove that with a dyno comparison of before and after. However, if you're a drag racer and .001 improvement in your ETs wins a race, you might appreciate 6 HP.

I'm confident the new engine is much more efficient than the LS3 and the HP increase with NPP may not be measurable. I added the remote actuated switch on my Grand Sport for the NPP since, when open and at steady speeds, it does have a minor drone to the exhaust sound. It doesn't bother me, but my wife wouldn't like it so I can close the valve when I want to.