i have run out of fuel at the track & refilled w/ VP Racing C12. it's a risky proposition since it's leaded fuel; this can foul oxygen sensors. without a doubt the car ran much better than on pump gas. i think that's because a lot of times, 93 octane at gas stations sits for awhile before it sees our tanks. octane turns into heptane (regular gas) over time, so the true octane rating of the fuel we purchase at gas station is somewhat less than 93 by the time we get it.
still, though, i don't think the computers in our car will try to optimize spark advance for anything beyond 91 octane (california fairy juice). a re-program of the ECU can widen the parameters to allow tuning to race fuel. companies like Revo will let you re-program on the fly for this. FYI, the difference is significant.
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