Matt@TYGA wrote:On my race 28 we used to run an "A" cylinder with "D" piston for fast tracks (0.047~0.053mm) and a "B" piston for short tracks (0.039~0.045mm). The reason was that at fast tracks the engine could be held flat out for longer and the bigger clearance piston allowed for this with less chance of nipping up. The tighter piston on short tracks was at peak rpm for only a short time so wasn't a problem.