Fuel engines run 4.5 to 4.625 stroke depending on the tuner - the longer stroke allows for more burn time and spark lead from what I have been told. Since they are limited to 500" the bore can vary slightly also by tuner but I would think the small bore would give more strength to the liner - RPM wise the fuel cars were approaching 10,000 RPM until they started limiting RPM by pulling the timing back at 8100 RPM to bring down speeds - but I would guess they are topping out close to 9000 RPM now