Then put two 3.8's in, you'll be fine. You must be the Kurt Busch of Micro racing.
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I really can't tell you which one is faster, just a comparison to what I've bought and tried. Right now my fastest motor is the NOS. But, the 3.8 is supposed to be the fastest on the market and if you have the juice to pump it, then that's what I'd get. Put it to you this way. If there was a difference, I can't see it being by that much. Don't forget the 3.8's are easier to come by too.