[SavageSS]

I'm looking to turn down the factory startup aggression on my '16 2SS with ARH full (w/cats) and stock NPP. On the Camaro 6th gen facebook forums someone suggested in HP Tuners changing Engine -> General -> Catalyst -> (Min ECT from 493 to 10 degrees). I checked with Pray who originally tuned the car with a previous owned and confirmed, but I wanted to post this here to benefit others and get some more info as to exactly what this setting does before making any changes.

(Note: the ARH headers to NPP is awesome, loud when you want it to be, Stealth mode is reasonably quiet but the factory built in aggressive startup across all modes which is a bit too much even in stealth mode when leaving the house at 6am with 2 little kids sleeping)

See attached screen shot. It's described as: [ECM] 2027 - Catalyst Warmup Max ECT. Why is the min set to 493 F and max set to 109 F from the factory?

Thanks!

[cmitchell17]

The MIN is set to 493F because it looks like someone set it there in order to disable the catalyst warmup. 493 is just the maximum interger value you can put in that table and you will never reach that value so catalyst warmup will never be enabled.

Catalyst warmup is just where it retards timing and injection event in order to try to burn more fuel outside of the engine and in the exhaust thereby creating more heat into the exhaust to warm up the catalytic converters, cats don't work real good until they are hot, so it cuts down on emissions, especially at cold start when they are high.

[cmitchell17]

I think the real reason its so loud at startup is the way the NPP actuators are controlled at startup, unfortunately we don't have anyway to control these, unless hp tuners or gives us access to tune the module that controls these valves.

You can put it in stealth mode before you start it, or either put it in snow/ice mode before starting and it helps a little.

[SavageSS]

Originally Posted by cmitchell17

I think the real reason its so loud at startup is the way the NPP actuators are controlled at startup, unfortunately we don't have anyway to control these, unless hp tuners or gives us access to tune the module that controls these valves.

You can put it in stealth mode before you start it, or either put it in snow/ice mode before starting and it helps a little.

If you set the mode to stealth or snow / ice the valves are closed fully. That gives us plenty of control.. On my 16 with ignition on (hold start for ten seconds) the exhaust valves will adjust to the selected mode in engine sound management.
Agreed is would be nice to give fill control to hp tuners but I'm actually pretty happy with the setup.

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[SavageSS]

Originally Posted by cmitchell17

The MIN is set to 493F because it looks like someone set it there in order to disable the catalyst warmup. 493 is just the maximum interger value you can put in that table and you will never reach that value so catalyst warmup will never be enabled.

Catalyst warmup is just where it retards timing and injection event in order to try to burn more fuel outside of the engine and in the exhaust thereby creating more heat into the exhaust to warm up the catalytic converters, cats don't work real good until they are hot, so it cuts down on emissions, especially at cold start when they are high.

Great explanation.. What are the factory values? That also explains why the exhaust smell is oddly strong. I have high flow cats but without a warmup cycle this would create even more stink. Thanks!

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[Silver2ssA8]

I like how agressive exhaust sounds at start up, it’s my weekend car so I’m not waking up any neighbors. In fact, I wish it would stay as loud as it is on cold start up. It seems to get quiet after 30 seconds or so

[SavageSS]

Originally Posted by cmitchell17

The MIN is set to 493F because it looks like someone set it there in order to disable the catalyst warmup. 493 is just the maximum interger value you can put in that table and you will never reach that value so catalyst warmup will never be enabled.

Catalyst warmup is just where it retards timing and injection event in order to try to burn more fuel outside of the engine and in the exhaust thereby creating more heat into the exhaust to warm up the catalytic converters, cats don't work real good until they are hot, so it cuts down on emissions, especially at cold start when they are high.

So if I understand this.. My car has catalyst warmup disabled which means normal amounts of fuel and timing during cold start. If I restore factory settings which enable catalyst warmup for cold start, how would that quiet startup?

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[GroundhogSS]

Originally Posted by cmitchell17

I think the real reason its so loud at startup is the way the NPP actuators are controlled at startup, unfortunately we don't have anyway to control these, unless hp tuners or gives us access to tune the module that controls these valves.

You can put it in stealth mode before you start it, or either put it in snow/ice mode before starting and it helps a little.

Perhaps with a couple of diodes and a switch, you could supply power to the dampers to close them before startup. Just remember to turn that circuit off or it will always be quiet.

[SavageSS]

Originally Posted by GroundhogSS

Perhaps with a couple of diodes and a switch, you could supply power to the dampers to close them before startup. Just remember to turn that circuit off or it will always be quiet.

No need for that. You can adjust exhaust valves with the car in ignition mode on a 2016. Not sure about other years. Even in stealth mode, startup is too loud. I'm asking how to quiet down the intensity of startup. The setting I referenced above seems to be related, however it appears catalyst warmup is already disabled in my tune

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[JFM-jr]

Originally Posted by SavageSS

I'm looking to turn down the factory startup aggression on my '16 2SS with ARH full (w/cats) and stock NPP. On the Camaro 6th gen facebook forums someone suggested in HP Tuners changing Engine -> General -> Catalyst -> (Min ECT from 493 to 10 degrees). I checked with Pray who originally tuned the car with a previous owned and confirmed, but I wanted to post this here to benefit others and get some more info as to exactly what this setting does before making any changes.

(Note: the ARH headers to NPP is awesome, loud when you want it to be, Stealth mode is reasonably quiet but the factory built in aggressive startup across all modes which is a bit too much even in stealth mode when leaving the house at 6am with 2 little kids sleeping)

See attached screen shot. It's described as: [ECM] 2027 - Catalyst Warmup Max ECT. Why is the min set to 493 F and max set to 109 F from the factory
I
Thanks!

I believe it is actually set at 10° from the factory and the change that disables the cat warmup is the change to the 493° figure. I have done this (and it actually may have been me that responded to you on Facebook) and it works great. I originally got this information from Parish on here. The car is still loud and high strung on the factory settings on an ice cold start with the valves closed. Once you alter these settings the car will start as if it is fully warmed up even if it's overnight cold. I actually enjoy the calm quiet cold starts. To each his own when I want it loud I open the NPP valves.

[cmitchell17]

Originally Posted by SavageSS

So if I understand this.. My car has catalyst warmup disabled which means normal amounts of fuel and timing during cold start. If I restore factory settings which enable catalyst warmup for cold start, how would that quiet startup?

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Disabling catalyst warmup shouldn't make it quitter, it should make it louder for longer since it raises idle. I think it may cut down on the injector noise as well, but that may be due to a split shot injection event.

[MR-02]

Cat overtemp protection switch is recommended left alone. What do you make of this info posted from a tuner in another forum , it says "Turning that switch off will destroy your cats" see last post below ..below..
Quote:

Originally Posted by gippy87
Its an option in HPTuners I believe called Catalyst or something. Disable this by setting the parameters so the car will never meet them and it will no longer make this sound at start up. It is very annoying and I hate being asked why the car sounds like that on cold starts..

Tuner Response was : This would not be the correct advice for someone who has cats, turning this switch off destroy the cats because you would have no Cat Overtemp protection.

There are better ways to do this.

Ted.

[JFM-jr]

I'm no tuner but catalyst warmup and cat over temp are 2 totally different parameters in HP Tuners. I think the settings referred to in this thread are emissions related and simply raise EGT's to jump start the cats into their effective operating temperature faster on cold starts where emissions can be higher until the motor is at operating temp. I have aftermarket cats tho and do this at my own risk. Cat over temp is for high RPM,heavy load conditions and the car reacts by dumping fuel into the motor to keep the cats from being damaged. Guys will see this at WOT in higher gears

[JFM-jr]

Originally Posted by cmitchell17

Disabling catalyst warmup shouldn't make it quitter, it should make it louder for longer since it raises idle. I think it may cut down on the injector noise as well, but that may be due to a split shot injection event.

Mine is disabled and it is unquestionably, undoubtedly quieter on cold starts there no comparison.