Is there any mod that can be done to start car with the valves closed? - Page 4

StateOfMind415 · 01-02-2017, 01:04 AM

Quote:

Originally Posted by G Fo12ce

Thanks guys. Now that's I've had a few mornings to play with it I agree. The menu stays up and it just takes a second to set it back to the auto mode. It's too bad you can't have a shortcut on the home screen that toggles these. That would be cool.

The shortcut would be to use the 'Mode' switch in front of the e-brake and set it to Ice/Snow mode (after holding push start for 5 seconds without turning on the car). This is the only mode that is tied to stealth mode. All other modes have a loud start up "bark". Once the car settles down, change it back to whatever mode you prefer and drive away.

franksredhot · 01-02-2017, 08:18 AM

As an owner of a non-NPP car, I don't believe the loud "blatt" sound has anything to do with the valves on your NPP. My car starts the same way, extremely loud and then quiets down after a few seconds. I think this has to do with the engine settings to start cold and warm up the cats quickly. My non-NPP car is so quiet during normal driving but still has the loud start like your NPP.

Megahurtz · 01-02-2017, 09:31 AM

Quote:

Originally Posted by franksredhot

As an owner of a non-NPP car, I don't believe the loud "blatt" sound has anything to do with the valves on your NPP. My car starts the same way, extremely loud and then quiets down after a few seconds. I think this has to do with the engine settings to start cold and warm up the cats quickly. My non-NPP car is so quiet during normal driving but still has the loud start like your NPP.

The way the engine starts is the same, but with NPP you can mitigate some of the sound by the valves. So yes, with NPP equipped cars, the valves do make a difference. With NPP the initial start is much louder than non NPP cars. I own a NPP car and test drove a non NPP car before I purchased. There is a significant difference in start up sound.

franksredhot · 01-02-2017, 10:46 AM

Does any one know what the difference is in the start when it is warm? My car will only make the loud sound for the first start in morning and the rest of the starts that day will be much quieter. I wonder if the AFM valve comes into play.

Megahurtz · 01-02-2017, 12:41 PM

Quote:

Originally Posted by franksredhot

Does any one know what the difference is in the start when it is warm? My car will only make the loud sound for the first start in morning and the rest of the starts that day will be much quieter. I wonder if the AFM valve comes into play.

Yes it's in the tune. One of the main things is timing/fueling/rpm based on coolant temps. The ECU is also trying to get the Cats warmed up as fast as possible for emission laws. This is a lot of the loudness after the initial flare up.

You will notice after you have driven the car and go to the store or something that does not allow the car to sit for many hours, the startup flare will be a bit milder and it will not be nearly as loud for the first 15 seconds after starting.

DetCam · 01-03-2017, 06:50 AM

External temperature plays a huge role. All summer long my car starts quiet... but when it gets cold out (below freezing) the start up "blat" get's louder. The colder it is, the louder the start (Michigan Winter, cold means 20 F, or even -10 F). So there is definitely something going on with an initial fuel dump or something in order to wake the beast on a cold morning. Setting the Engine Sound Management to "Stealth" in the center console definitely makes a difference... but when it's freezing cold out, you will still get a "blat" on startup (just not as much). I find it works best to have driven the car for a little while in full stealth mode before parking it. It's almost like it takes a little time to settle in completely.

(Also: I'm thinking if the system is designed to breath a little better on startup and release some pressure, I'm not sure how comfortable I'd feel bypassing the system and trying to force things closed. That initial "cough" on a really cold day helps clear it's throat, I'm not sure I'd want to stifle that cough entirely).

EFI Tuning · 01-03-2017, 07:17 AM

There is no pressure to release on startup. Keeping the valves closed wouldn't hurt anything. It would be the equivalent of not having NPP.

G Fo12ce · 01-03-2017, 12:09 PM

Quote:

Originally Posted by StateOfMind415

The shortcut would be to use the 'Mode' switch in front of the e-brake and set it to Ice/Snow mode (after holding push start for 5 seconds without turning on the car). This is the only mode that is tied to stealth mode. All other modes have a loud start up "bark". Once the car settles down, change it back to whatever mode you prefer and drive away.

I didn't know snow/ice was set to stealth on the NPP. Interesting, I'll give this a try tomorrow. Thanks.

StateOfMind415 · 01-03-2017, 06:14 PM

Quote:

Originally Posted by G Fo12ce

I didn't know snow/ice was set to stealth on the NPP. Interesting, I'll give this a try tomorrow. Thanks.

Page 231 in your manual =D

http://www.chevrolet.com/content/dam...ers-manual.pdf

G Fo12ce · 01-04-2017, 06:28 PM

Quote:

Originally Posted by StateOfMind415

Page 231 in your manual =D

http://www.chevrolet.com/content/dam...ers-manual.pdf

I'll take your word for it. I did it this morning and it worked liked you described. Thanks for doing the reading for me lol

01-02-2017, 08:18 AM	#44
franksredhot Drives: 2016 Red Hot Camaro 1SS A8 Join Date: Jun 2016 Location: Queens, NY Posts: 114	As an owner of a non-NPP car, I don't believe the loud "blatt" sound has anything to do with the valves on your NPP. My car starts the same way, extremely loud and then quiets down after a few seconds. I think this has to do with the engine settings to start cold and warm up the cats quickly. My non-NPP car is so quiet during normal driving but still has the loud start like your NPP.

01-02-2017, 10:46 AM	#46
franksredhot Drives: 2016 Red Hot Camaro 1SS A8 Join Date: Jun 2016 Location: Queens, NY Posts: 114	Does any one know what the difference is in the start when it is warm? My car will only make the loud sound for the first start in morning and the rest of the starts that day will be much quieter. I wonder if the AFM valve comes into play.

01-03-2017, 06:50 AM	#48
DetCam Drives: 2016 1SS (12/10/2016) Join Date: Jul 2015 Location: Troy MI Posts: 169	External temperature plays a huge role. All summer long my car starts quiet... but when it gets cold out (below freezing) the start up "blat" get's louder. The colder it is, the louder the start (Michigan Winter, cold means 20 F, or even -10 F). So there is definitely something going on with an initial fuel dump or something in order to wake the beast on a cold morning. Setting the Engine Sound Management to "Stealth" in the center console definitely makes a difference... but when it's freezing cold out, you will still get a "blat" on startup (just not as much). I find it works best to have driven the car for a little while in full stealth mode before parking it. It's almost like it takes a little time to settle in completely. (Also: I'm thinking if the system is designed to breath a little better on startup and release some pressure, I'm not sure how comfortable I'd feel bypassing the system and trying to force things closed. That initial "cough" on a really cold day helps clear it's throat, I'm not sure I'd want to stifle that cough entirely).

01-03-2017, 07:17 AM	#49
EFI Tuning Drives: 2016 Camaro SS Join Date: Oct 2016 Location: Mount Dora, FL Posts: 792	There is no pressure to release on startup. Keeping the valves closed wouldn't hurt anything. It would be the equivalent of not having NPP.

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