Although the aluminum M/T heads on my blown-alky hemi are cast with coolant passages, I've always run with no coolant. Tractor pulling doesn't have the duration of land speed, but depending on the track, we could be at full power for about 20 seconds. I've safely made 3 runs in about a 10 minute period when necessary (full-pull near end of the class, then a couple of pull-off runs). The hemi I''m building for the lakester will definitely have coolant, but I don't foresee much demand on the cooling system. For mile events I might even get away without circulating the coolant.