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I had my car on a friend's lift to day and he noticed what appears to be an adjustable exhaust. I have had the car over two years and despite regular cleaning of the tips I had not noticed the solenoids. They appear to vacuum operated and the dampers are wide open, which I assume gives the loudest exhaust note. I can find find no obvious method of adjustment. Does anyone have any idea how these are supposed to work and where would be the likely location of a switch? I can find no name name on the exhaust system. I know this was a factory option on some cars but I have no clue as to whether these are factory or after market.
They look OEM, not aftemarket. I have the same system. If not modified and working properly, they operate without user intervention. You have to drive quite aggresively for those valves to open to gain an extra 6HP. Otherwise they remain closed when driving around under normal driving conditions.
They look like factory NPP option mufflers to me. The butterfly valves are vacuum operated and need vacuum to close. Engine off = no vacuum so they should be open. If it’s the OEM system then:
Below 30% throttle and 3,500 rpm the valves are closed. Above 30% throttle and 3,500 rpm the valves will open. Between 30% throttle and 80% throttle and above 3,500 rpm the valves are open. Above 80% throttle and above 2,800 rpm the valves are open.
Look for the option code NPP on the label on the side of the glovebox. If that’s there, then you can expect the above behaviour. If it’s not there, then the mufflers have been retrofitted and one of a variety of self built or aftermarket solutions may be in play to manually operate the valves. There’s also a Mild2Wild control unit which you can easily install that either keeps the valves open all the time, or defaults to OEM operation. Or you can just pull the EXHMDL fuse, and they’ll stay open all the time.
Yep… You’ve got what looks like a stock NPP system. Pull the far lower right fuse in the passenger foot well. It will sound amazing. I pulled mine and haven’t looked back since.
I must admit though, I am rather surprised that you had a C6 for 2 years and knew not of the dual-mode exhaust options functions. You should hang around here more often…
Last edited by RobertCorvette; Jul 2, 2024 at 06:40 PM.
Jeez, open up the glove box and read the RPO codes. If NPP is on there it came from the factory, if it's not it was added later.
Done.
Oops, sorry fats, didn't mean to steal yer thunder.
I just pulled my fuse and keep it loud. Did purchase this foot switch Mild 2 Wild Foot to quiet it when I want to but I have not made time to install it.
My goal is to get headers and tune in next 6 months. Thinking I want that switch then when pulling into neighborhood. Right now the loud is not annoying in anyway.
I knew it was an option, I just didn't think this car had it since its a 1LT. It's my 4th Corvette. I just keep them nice and drive them, not obsess over them. Thanks for all the replies. Good information.
NPP was a stand alone option on base cars from 2008 up and GS from 2010 up. It wasn’t included in any packages. On my 4LT GS, for example, it was ordered separately. If you have that option on a 1LT car, the original owner made a wise choice.
Nice color. I’ve heard of owners putting split collars on the actuator shafts so that the butterflies can’t be pulled completely closed. I’ve thought I might try that at some point, even though I mostly drive using the M2W unit set to off (valves open). I have to say with the valves closed, it doesn’t sound like a Corvette at all. Way too quiet. My Caddy was louder.
They look like factory NPP option mufflers to me. The butterfly valves are vacuum operated and need vacuum to close. Engine off = no vacuum so they should be open. If it’s the OEM system then:
Below 30% throttle and 3,500 rpm the valves are closed. Above 30% throttle and 3,500 rpm the valves will open. Between 30% throttle and 80% throttle and above 3,500 rpm the valves are open. Above 80% throttle and above 2,800 rpm the valves are open.
Look for the option code NPP on the label on the side of the glovebox. If that’s there, then you can expect the above behaviour. If it’s not there, then the mufflers have been retrofitted and one of a variety of self built or aftermarket solutions may be in play to manually operate the valves. There’s also a Mild2Wild control unit which you can easily install that either keeps the valves open all the time, or defaults to OEM operation. Or you can just pull the EXHMDL fuse, and they’ll stay open all the time.
Thanks for the incredibly detailed information. The car sounds great under acceleration. Apparently that's why. I just never really thought about a low end trim level having that option. I can't stand sooty exhaust tips so I'm always cleaning them. I just never noticed the actuators. I just though it was part of the exhaust clamps. So much for my observation skills. I also always thought the NPP exhaust had manual activation and assumed there was a switch somewhere. Thanks for broadening my understanding. That's why I'm a lifetime member of this forum.
Thanks for the incredibly detailed information. The car sounds great under acceleration. Apparently that's why. I just never really thought about a low end trim level having that option. I can't stand sooty exhaust tips so I'm always cleaning them. I just never noticed the actuators. I just though it was part of the exhaust clamps. So much for my observation skills. I also always thought the NPP exhaust had manual activation and assumed there was a switch somewhere. Thanks for broadening my understanding. That's why I'm a lifetime member of this forum.
You can do that very easily with a mild to wild switch. I had the one that mounted in the dead pedal so if you wanted it on or off at will you just hit it with your left foot. Like the old time hi beam switch in the old days. Post number 4 in the thread. https://www.corvetteforum.com/forums...tall-help.html
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NPP Exhaust
