AXIS89

Hey guys. I’ve owned my C7 for about a month now and I’ve noticed sometimes the exhaust is quieter than usual and I was curious if anyone else had noticed the same thing. I can notice a decreased volume and throatiness that doesn’t seem to go away until I restart the car later. Sometimes even the throttle response feels decreased. I tried searching and found one other thread but aside from some discussion on possible contamination on the mass airflow sensor it was a bit of a dead end.

laserdude2215

When my exhaust is quieter than usual, I just step on it hard and all is good again.

CocoVette

Usually cold starts are louder, as it warms up, less pleasure

JerryU

IF you have NPP the butterflies in the outer pipes, that essentially bypass the muffler:
Are open when you start the car. Lasts for a short time, then they close.
They then open at various rpms depending on Drive Mode setting:
In Track they open at about ~1700 rpm
In Touring they open at about ~2500 rpm

You can set them so that are always in Track Mode regardless of Drive Mode (where I have mine set.

You can also pull the right fuse so they never close and live wit a drone on the highway!

dvilin

NPP read all about it.

Zjoe6

Your Track rpm point is spot on. I personally would leave it as is and not pull the fuse. I actually like how it quiets down when I’m cruising along at 70+ mph. The drone gets to my ears.

etaylor14

the npp when set to sport mode will be open in 1st to 5th gear and will close in 6th 7th and 8th. If you get on it a little they will open up again until you ease off the throttle. Listen for them to open and close.

Vetteman Jack

Yeah, if you have the NPP exhaust on your car, the change in volume is most likely due to the opening and closing of the butterfly valves in the exhaust. It sure sounds good when the valves are open.

roadbike56

There is no doubt that the valves on my 2014 have changed over time. It definitely stays open a little longer and opens up a little easier than when I first bought it. Of course, I'm not complaining

Rebel Yell

As any Service is apt to say "They'll do that". Completely normal. You can pull the fuse to the system, and the exhaust will stay open all of the time. Right off hand I can't remember the fuse number........I'm gettin' old don'tcha know.

AXIS89

I suppose I should have clarified that I do have NPP and am pretty much always in sport mode. I don’t think it’s related to the opening and closing of the valves, unless they are only partially opening sometimes. The changes in sound I am noticing still apply after everything is up to temp and despite the same driving style there are notable differences in volume and tone/throatiness. For example, downshifting with the rev matching on usually sounds fairly load and throaty. Whereas it is much quieter and subdued when I’m noticing the quieter exhaust despite shifting at the same RPMs. The biggest part that seems odd is how different the gas pedal feels. The other night I felt like I wasn’t even pressing the gas until I pressed a decent bit more than usual.

Rebel Yell

With mine (A8) set in sport mode the valves will be open from take off until around 1500-1700 rpm cruising speed, and the valves seem to stay closed until I come to a complete stop again. Does that sound anything like you're having?

bearphoto

You might be referring to the sound difference when the car goes into V4 mode versus V8 mode. Assuming you have an "automatic" trans just drive the car in M (manual) mode and use the paddle shifters, then your car will never go into V4 mode. If your car is an M7 trans it will never go into V4 unless you set the car for "eco" ! Who would buy a corvette and drive it around in V4 mode is beyond me but....to each their own.

Fuse 42 in the fuse box under the hood will keep those rear exhaust pipe valves open all the time.

Zjoe6

The fuse number changes depending on your year so check the manual.