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Re: 93 octane
Yeah, it does have a small effect, but the quality of the fuel has a MUCH greater effect than altitude does. To keep things simple, I said to ignore it because you can't just assume that higher altitude means you can use lower octane and get away with it.
With higher altitude, there is lower O2 density in the air, which makes the fuel less likely to react and be oxidized (combust). This means that fuel at sea level will be a little more resistant to reaction at altitude, therefore, it will act like a little higher octane fuel in that regard. SO, the timing can accordingly be tuned a little more aggressively. HOWEVER, because there is less O2 in the air, less fuel must be used to maintain a proper AFR. This is more of a factor in the performance of the car than the octane of the fuel is. That is why I said what I did.
Case in point, a tune written for 94 at sea level has to have the ignition retarded by about 5 degrees and also needs about 12% fuel pulled in order to keep knock and timing correction at a reasonable level. This is mainly because of the difference in fuel quality (and the damn ethanol we get here in our 94), and even the high altitude can't compensate for that.
Yeah, it does have a small effect, but the quality of the fuel has a MUCH greater effect than altitude does. To keep things simple, I said to ignore it because you can't just assume that higher altitude means you can use lower octane and get away with it.
With higher altitude, there is lower O2 density in the air, which makes the fuel less likely to react and be oxidized (combust). This means that fuel at sea level will be a little more resistant to reaction at altitude, therefore, it will act like a little higher octane fuel in that regard. SO, the timing can accordingly be tuned a little more aggressively. HOWEVER, because there is less O2 in the air, less fuel must be used to maintain a proper AFR. This is more of a factor in the performance of the car than the octane of the fuel is. That is why I said what I did.
Case in point, a tune written for 94 at sea level has to have the ignition retarded by about 5 degrees and also needs about 12% fuel pulled in order to keep knock and timing correction at a reasonable level. This is mainly because of the difference in fuel quality (and the damn ethanol we get here in our 94), and even the high altitude can't compensate for that.
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