geraldschumann

Without NPP is the confguration the same as the loud setting with NPP? I have measured the sound difference with NPP. The quiet setting is 3dB quieter than sport setting with NPP which makes the sport setting twice as loud, aproximately. My measurements were consistent with the sound meter being in the same spot for both NPP settings.

Also side question. Is the exhaust config change with NPP only the back two valves or are there different changes upstream in the exhaust system?

What is the Stealth setting? Only the aft two balves?

These questions may have been asked and answered before but with time and changes by GM it is all subject to change.

Many thanks and regards.

eboggs_jkvl

NPP has 2 valves that the stock system does not have. When the valves open, the exhaust travels a different path and it is louder. Supposedly, you get 5 HP with it.

Up until the 17', there are 2 valves upstream of the NPP. These valves are activated when the car goes to 4 cylinders. Something about stopping the car from sounding like a 4-banger. They've removed the upstream valves on the newer models. It might be only on the Z06 but that's what I read. I think the M7 might lose the upstream valves too.

Elmer

Rebel Yell

If I understand correctly you're asking what the standard exhaust sounds like. If so, the exhaust on mine is a bit louder than the Borla Touring I had on my C6. So, not very loud at all.

Larry/car

The standard version has three inch pipes that are sectioned two on each side open at all times. The NPP has four horns equally spaced in the surround opening, only two pipes are open in the quite mode (in use those open pipes get dirty/sooty and the system looks odd after a few miles). The standard system is ok with me, it has an attitude under power, I like the sectioned look of the pipes better and you save about $1,200 including the added tax.