Heres' some numbers for you. The 305 has a bore of 4.25 x 3.58 stroke. The 351 has 4.56 x 3.58. The 401 is 4.87 x 3.58 the 478 is 5.125 x 3.86. These engines are about indestructable. Coffee can sized pistons on the last two almost. Not fuel efficient unless some headwork is done and proper gearing. The 305 and 351 with hwy gears are too bad on fuel and pull real well. If you put on an atomizer or a hydro unit it will help you get about 4 mpg more. I hope this will help you out. Henry