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Originally Posted by Dean
OK, and with good old pvnrt, we have less, hotter air... Even at 15.3 it is still less hotter air.
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Less boost at a given altitude and temperature is always less air, just a bit cooler. More boost gives you more power at all altitudes until you hit the point of uncontrollable knock.
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Originally Posted by Dean
Now with less air(CFMs), shouldn't the intercooler be more efficient(or maybe that is a bad word) More able to reduce the temperature of that given volume assuming sufficient cooling of teh intercooler itself?
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Yes and no. Lower boost makes it easier for the air to flow through the IC, but the lack of air molecules flowing over the outside of the IC makes the cooling efficiency worse. Double whammy from the altitude when you're trying to compaensate for the atmospheric pressure.
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Originally Posted by Dean
But with less air, slightly hotter or not, we have less pressure at or before combustion/detonation, so thus, less octane required... Or so was my understanding.
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Yeah pretty much. See, "high" boost pressures require more timing advance than "low" boost pressures, because the flame front moves faster the higher the cylinder pressure is (more molecules bumping into each other more often at higher speeds = faster checmical reactions). Because the flame moves slower at lower boost making less power, MBT is not as high numerically. Reduced ignition advance allows for a lower octane gasoline. that's why I would think it would be pretty easy and safe to make an 89 octane commuting/economy map for use up here. Run like 13 psi and keep your AFRs around 11.5-12:1 and you should be able to run 89 all day long, even at full throttle.