04-13-2021, 01:27 PM | #1 |
Drives: 2016 Camaro 2SS Join Date: Sep 2015
Location: Cincinnati Ohio
Posts: 455
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NPP Front Valves
I tried search but it seems broke...Question...when i start car cold...the NPP exhaust level is very loud (rear valves open running in track mode). After about a minute it quiets down. I would assume that is front valves(near cats) closing? IS there a way to stop that from happening so exhaust is as loud when warm as it is during a cold start?
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04-13-2021, 01:42 PM | #2 |
Drives: 2018 Camaro SS 1LE M6 Join Date: Oct 2018
Location: Northern California
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There are no front NPP valves?? Before you turn your car off set the exhaust mode to stealth or tour.
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04-13-2021, 01:55 PM | #3 |
Drives: 2018 Chevrolet Camaro 2SS 1LE 6M Join Date: Jul 2019
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When you first start the car, the valves are open-even in TOUR mode. They close after a couple of seconds and you will notice the exhaust note change. There are no front NPP valves.
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04-13-2021, 02:08 PM | #4 |
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There's no front valves the change in sound is RPM and extra fuel to warm up the cats, it does that in 30-60 seconds and why you see the RPM come down and the sound change.
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04-13-2021, 02:21 PM | #5 | |
Drives: 2017 ZL1 Join Date: Jan 2017
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Quote:
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04-13-2021, 03:21 PM | #6 |
Drives: 2016 Camaro 2SS Join Date: Sep 2015
Location: Cincinnati Ohio
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I want it loud like it is at startup...trying to figure out if there is a way to keep it loud vs getting quieter after so many seconds..my npp settings are always either track or sport..something is causing the exhaust note to get quiet after cat warmup..i always thought it had to do with front afm valve open/closing...
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04-13-2021, 03:25 PM | #7 | |
Drives: 2017 Camaro SS, 2011 Corvette GS Join Date: Feb 2019
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04-13-2021, 03:32 PM | #8 |
Drives: 2016 Camaro 2SS Join Date: Sep 2015
Location: Cincinnati Ohio
Posts: 455
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the npp valves are always open the way i have the settings...if it had something to do with npp valves closed at startup...the exhaust would get louder after warmup....not quieter after so many seconds at cold startup....the extra loudness of the exhaust is only when car is started cold...when its warm the exhaust level is always the same at start...as previous poster mentioned...it has something to do with cat warmup...i always thought it was front afm valves open more to let cats warm up faster...just trying to determine if there is a way to capture and keep exhaust level the same loudness as it is at cold startup...all the time...i dont want it quiet..i want it louder
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04-13-2021, 03:48 PM | #9 | |
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04-13-2021, 05:37 PM | #10 |
Drives: 2016 Camaro 2SS Join Date: Nov 2016
Location: North Jersey
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There's no way to make it that loud all the time unless you go catless.
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04-17-2021, 02:17 PM | #11 |
Drives: 2021 Camaro 2SS 1LE manual Shadow G Join Date: Oct 2020
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Like some have mentioned, pull the F51 fuse. This will keep the valves open no matter what, if you don't care about needing to run in tour mode. If you always run in sport or track then it's a non issue. Even in track the valves still close at certain speeds. Next would be chopping off the secondary cats. Try that, if you still want louder, then it's axel back or catback exhaust terriotory.
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04-17-2021, 02:24 PM | #12 |
Drives: 2021 Camaro LT1 Join Date: Apr 2021
Location: South Carolina
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Even with the NPP valves locked kept open, the AFM valves will still close whenever it goes into V4 mode. I think it can be turned off with a tune. I actually notice the transition into V4 mode more when I have the NPP valves open all the time.
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04-17-2021, 03:29 PM | #13 |
Drives: 2018 Camaro 2SS A8 Join Date: Dec 2019
Location: Windsor, Ontario, Canada
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With HP Tuners you can disable the front AFM valves and program the rear NPP valves to do whatever you want in any mode, also you can disable the cat warmup mode and you will still get that loud startup flare at first. There's even a rumble mode on startup you can disable or enable in each mode but it seems to have little to no effect.
I have TSP 2" LT's and no cats with the front AFM valves disabled and wide open 24/7. It is borderline abnoxious loud starting the car with the NPP valves wide open, but it sounds buzzy and shit with them closed on startup. So its really your choice, but you need HP Tuners to have an real control over the options.
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