Like all the members of the J-6 Whirlwind family, the R-540 had larger cylinders than the R-790. The piston stroke of 5.5 in (14.0 cm) was unchanged, but the cylinder bore was expanded to 5.0 in (12.7 cm) from the R-790's bore of 4.5 in (11.4 cm). While the R-790 was naturally aspirated, the R-540, like the other J-6 engines, had a gear-driven supercharger to boost its power output.