CAMARO6 - View Single Post - Is Stealth Mode Available in the LT1 Trim with NPP?

cmitchell17 · 12-01-2020, 08:11 PM

Even with "stealth" mode on (valves closed 100%) it is still pretty loud in my opinion on startup, enough so I could see some do-gooder neighbors still getting mad. The loudness is made worse on a cold start since it retards the injection and spark timing and increases RPM and throttle on cold starts to help warm up the cats. The retarded timing (in my opinion) makes the exhaust louder as well.

I can't believe GM let the Camaro with the NPP out of the factory as loud as it is during startup, but that is what it took to meet cold start emissions I guess and there's probably no immediate noise level requirement.

I've never heard a non-NPP in person but I would imagine it is a lot more quiet, especially during the initial startup rev up. Also I believe the stock tuning opens the valves during startup for the supposed "cool rumble effect". Although I can't remember it might close during startup if you force stealth mode, which you would have to force it through the menu, since I think it defaults back to tour mode (where the stock tuning sets the NPP valves fully open on startup) (like 6sigma said above).

HP Tuners can set the startup rumble and customize the opening on all the modes however you want it though.

12-01-2020, 08:11 PM	#8
cmitchell17 Drives: 17 2SS, 8L90, Cam, Heads, E85 Join Date: Dec 2016 Location: US Posts: 1,213	Even with "stealth" mode on (valves closed 100%) it is still pretty loud in my opinion on startup, enough so I could see some do-gooder neighbors still getting mad. The loudness is made worse on a cold start since it retards the injection and spark timing and increases RPM and throttle on cold starts to help warm up the cats. The retarded timing (in my opinion) makes the exhaust louder as well. I can't believe GM let the Camaro with the NPP out of the factory as loud as it is during startup, but that is what it took to meet cold start emissions I guess and there's probably no immediate noise level requirement. I've never heard a non-NPP in person but I would imagine it is a lot more quiet, especially during the initial startup rev up. Also I believe the stock tuning opens the valves during startup for the supposed "cool rumble effect". Although I can't remember it might close during startup if you force stealth mode, which you would have to force it through the menu, since I think it defaults back to tour mode (where the stock tuning sets the NPP valves fully open on startup) (like 6sigma said above). HP Tuners can set the startup rumble and customize the opening on all the modes however you want it though.