The 25/27 (and the 747 cc 30 hp, for that matter, as well as the 28 efi) are small block engines, but with a decent sized displacement (725 cc--the only consistent difference in parts between 25 and 27 hp models is the camshaft). They have the same size block (different bores) as all the Commands (624 cc 18-20 hp engines, and the 674 cc 22-23 hp engines). I believe all the strokes are the same (except the 30). Kohler's "big block" engines are 34-40 hp and 999 cc. The kawasaki FX series 31 (and current 27) are both larger displacement engines (852 cc); the 34 and 37 are 999 cc. Their 19-25 hp engines are all 675 cc (the difference being the carb, although some 25's have oil coolers).