2013 Denali TM, Add-Ons, Speed Limit and Altitude

[wamf16]

I have loaded the Diablo Tune on my Denal 6.2L and have a few questions:

1. Do I need to get a custom tune to account for my Airaid Jr and Borla exhaust, or will your tune and truck ECM account for those?

2. I assume the truck comes with the TM on? If so, what turned it off...the Diablo Tune or the Trans Firm Shift Tune? Is TM off completely off or a reduced percent? With TM on the high RPM shifts still felt harsh? Low RPM shifts are nice and crisp either way. This truck is a daily driver so I don't want to wear out my tranny! What do you suggest here?

3. Does speed limiter off limit my top speed to redline?

4. I am at 4000 feet. I assume 91 Octane is good enough for the Diablo Tune up here?

Thanks for your time...Jim

[Grumpy_Aero_Guy]

I have loaded the Diablo Tune on my Denal 6.2L and have a few questions:

4. I am at 4000 feet. I assume 91 Octane is good enough for the Diablo Tune up here?

Thanks for your time...Jim

I may be able to shed a little light on this one. The question regarding 91 octane vs. altitude is somewhat a "wrong question". Please don't take this the wrong way---i'll try to explain.

The octane rating of a fuel simply indicates its "resistance to detonation". Higher octane, more resistance to detonation. An Internal combustion engine wants the fuel to detonate exactly when it should, not before. "Before" = ping, or knock = potential damage if bad.

High compression ratio engines "coax" the mixture to want to detonate sooner through compression heating on the compression stroke, hence one needs MORE resistance to detonation with compression ratio, all other things being equal. That's why racing fuels are "high octane" fuels. They have no more energy per unit mass of fuel. they just allow you to compress the mixture much more while resisting detonation. Then, you have more MEP, and hence more HP.

Now, pre-detonation, or knock, is a finction of many things, including spark timing, load, and, importantly, air fuel ratio. Lean mixtures and rich mixtures resist detonation more than perfect (stoichiometric) mixtures, generally stated.

In fact, a knock sensor pulls timing out if incipient pre-detonation is detected. Knock is NOT a strong function of altitude in modern engines---BECAUSE, the mass air sensor along with other inlet air measurments can tell the pooter to a high degree of accuracy what the incoming mass of air is to the engine, regardless of the altitude (within reasonable limits of altitude). Hence, the pooter can provide exact air fuel ratio based on that mass calculation. Hence, you are back to parity on the "is 91 octane good enough for me at this altitude" question.

the question transforms itself to "is this 91 octane fuel good enough to resist detonation long enough before spark ref where my timing is set". it really isn't a function of altitude, per se, anymore. I hope this is clear. If it is good enough at sea level, it should be good enough at altitude.

Back in the day, carb jets had to be swapped at altitude to spray less fuel, due to less air density, all other things being equal. In the world of pooters, no longer an issue.

Hope this lecture helps.