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Originally Posted by H3PAC
I would assume that the expert engineers at GM would have already programmed the vehicle to perform optimally - i.e. the best combination of power/fuel efficiency/emissions, etc. I see programming devices advertised for sale to the conusmer and I wonder, why would an amateur playing around with these settings be able to do a better job than an entire professional team? Please don't misunderstand me - I don't mean to be disrespectful, I'm just trying to understand what the goal of reprogramming is. Can anyone please clareify this?
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First of all I really like GM, and I never bought anything other than a GM vehicle.
I some cases I agree with your thoughts. However, the amount of testing on the C6 Corvette&Z06 was way more extensive than the H3. So the tuning of the Corvete is much closer to optimal than the H3's, in my opinion. I feel GM has limited money/resources which limits development. Also, GM has to design to some extreme conditions such as temperature, fuel grades, etc which dictate the amount of conservatism in the tuning. For example, I think there is a TSB for the I5 for rough idle requiring a PCM reflash. So there is one example of where the experts didn't take everything into account the first time. OK, so everyone makes mistakes.
For example, if you have good quality gas and you don't operate in extreme temperatures, you can re-optimize you programming to your environment. Ask any tuner what the optimum A/F ratio is for best power and you'll get something like 12.8 - 13.1:1. However, GM has a 11.3 commanded A/F ratio for wide open throtle (WOT) for max power. Why? 11.3 is more conservative and provides more margin in case of problems. However, if you have a custom tune you can get the optimal A/F for more power. The same can be said for the timing or torque managment.
It's not that GM doesn't know how to optimise performance (look at the C5R), but is forced to for manufacturing tolerances, warranty issues, etc.
So a custom tune is one made for your vehicle - kinda like a custom suit.