[tecboy]

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?

[BruceWayne1LE]

There are no front NPP valves?? Before you turn your car off set the exhaust mode to stealth or tour.

[NA18CamaroSS]

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.

[WhiteMale]

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.

[LiqTenExp]

Originally Posted by tecboy

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?

The front valves are associated with AFM (4 vs 8 cyl). If you have the NPP option there are valves near the suitcase muffler that closes/open based on settings that skip around the muffled section of muffler. Part of start up involves catalyst warmup that will make it sound louder till it completes (when ECT >=109°F). If you leave it in stealth mode before you shutdown or power up car (5 second hold) and select stealth mode it will help cut down on the noise.

[tecboy]

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...

[Spaceme1117]

Originally Posted by tecboy

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...

Pull the NPP exhaust fuse in the under hood fuse block. Will be in loudest mode all the time.

[tecboy]

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

[lt4camaro]

Originally Posted by tecboy

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?

Pull the fuse for the NPP valves. The front valves are for AFM, you have no control over those. Also, the loud start is the computer allowing a rich mixture to ignite the Catalytic converters quicker to control warm up emissions, thats why the idle speed drops and the engine tone changes in 30 seconds.

[srcstc]

There's no way to make it that loud all the time unless you go catless.


Sent from my iPhone using Tapatalk

[dannbla]

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.

[WraithRider]

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.

[BDPhoto519]

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.