Not sure, but I think it is a 6.5 HP motor ... with a restrictor plate. I'm guessing upwards of 20 - 25 mph at most (but really, I'm clueless). Slow enough, I felt at ease shooting from the edge of the track (with the proprietors permission). When they would spin out, they could only make it about halfway up the bank.
Yes, panning was definitely part of the equation. The lighting was pretty low, and I was shooting 1/100, f/2, ISO 3200 (i.e. no flash, for obvious reasons) ... and still had to lift it quite a bit in post. 1/100 still blurs the entire car, if I don't pan along with it very well ... I got quite a few of those, too.
