And dal, I just read your thread and see you did the same thing--you wanted about +7 psi so you picked the bigger pulley to take the air pressure into account. Nice review thread. Do they use a MAP sensor to tune? If so I would guess your tuner could have just guessed rich on the higher (low altitude) manifold pressure ranges and you would be good to go.
The interesting thing to me about the altitude issue is that, while it slows the cars down at low speeds, at high speed power to drag starts to dominate instead of power to weight. Since drag is also reduced by the altitude--a little more than power actually--the car gets some of its speed back.
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