We want to add inches to our 401 because inches add power. Our 370-inch engine makes about 465 hp on pump gas or about 1.25 hp per cubic inch. In theory, the same combination of parts on a 412-inch engine will make 517 hp. Another theory says that for each 10 hp you get 0.10 seconds at the drag strip. Therefore, 52 hp is equal to a half second at the drags. But there’s more. A larger engine will move more air so the cam, intake, heads, and carb can be larger as well, making the percentage of power gained even better.