Inside the stock axle back before the muffler, we cut it open to find out.
11-09-2013, 12:49 PM
#1
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Inside the stock axle back before the muffler, we cut it open to find out.
Here is a picture from the outside of the exhaust, of the valves before the muffler.
This appears to be a valve that when closed, makes the entire exhaust have to breathe through a 1/2 inch hole. This is supposedly used to quiet down the exhaust when the AFM kicks in. To each his own, but I don't want something like this inside the exhaust system of my corvette, and when we build our high performance exhaust system for the C7, it will no longer utilize this function. The actuators can be removed by 3 screws and stay plugged in and mounted out of the way so there will not be a check engine light, or they can be fully removed and you will have to get the check engine light disabled (if there is one, we haven't tested it yet, we will know soon).
This appears to be a valve that when closed, makes the entire exhaust have to breathe through a 1/2 inch hole. This is supposedly used to quiet down the exhaust when the AFM kicks in. To each his own, but I don't want something like this inside the exhaust system of my corvette, and when we build our high performance exhaust system for the C7, it will no longer utilize this function. The actuators can be removed by 3 screws and stay plugged in and mounted out of the way so there will not be a check engine light, or they can be fully removed and you will have to get the check engine light disabled (if there is one, we haven't tested it yet, we will know soon).
11-09-2013, 06:44 PM
#2
Thanks for posting...sure am glad I did not spend a grand on that gimmick.
11-09-2013, 07:14 PM
#4
Team Owner
Like Mike said, that is the valve for 4 cylinder mode so it doesn't drone or sound bad in v4 mode. The dual mode exhaust is different and back in the mufflers.
11-09-2013, 07:18 PM
#5
Le Mans Master
It's only restrictive in 4 cylinder mode anyways making it a nonissue.
11-09-2013, 08:16 PM
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This is on the dual mode exhaust as well in the same spot. The valve even at open position does still cause a slight restriction. The fact that we don't know what its doing all the time makes me want to get rid of it anyway.
11-10-2013, 01:01 AM
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What harm could it possibly cause the engine under part load operation?
Put a Kiel probe/pitot tube in the exhaust with the valve in (open position) and with the valve ground out. I'd be surprised if you saw a difference of more than one kPa, which is .145 psi.
Last edited by arghx7; 11-10-2013 at 01:03 AM.
11-10-2013, 05:24 AM
#10
Safety Car
i'd be more worried about the back pressure and possible CEL in v4 mode more than i would the exhaust note. i'm sure it will be tuned out down the road with a full exhaust setup.
11-10-2013, 05:25 AM
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I'd keep that valve on the car to ensure the 4 cylinder mode works as intended.
11-10-2013, 05:53 AM
#12
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I was thinking about getting an after-market exhaust. But after reading about the complexity & engineering hours spent by GM to tune it correctly I decided to go with the factory upgraded exhaust.
11-14-2013, 10:33 AM
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If the C7 is anything like the new trucks, that valve helps to keep the car from sounding like a fart in a bathtub when in 4cyl mode. We had a customer put a cat back on his new Silverado and it sounds like a ricer when it switches to 4 cyl.
11-14-2013, 11:44 PM
#19
Le Mans Master
Is it possible that the 4 cylinder valve can be set up, whereas the valve retracts outside of the exhaust pipe, in a manner so that it is not a restriction on the flow of exhaust.
11-15-2013, 06:18 AM
#20
Mike- when you were probing underneath, do you know or did you notice if there is another actuator harness plug (but not used/unplugged) for non-NPP present in your car? It would be found or located somewhere aft of the muffler. I'm wondering if GM has the plug present on all C7's and obviously it's used if the car has NPP but simply not plugged-in for cars w/o NPP option.