The hp numbers for the 318 are inflated, my 318 marine 4 barrel with a bigger cam is only 225 hp. My cousin thought the same, until we raced. The 318 got the jump, but my 273 passed him like he was standing still. Horse Power is in the heads, all things being equal. Cubic inch dictates what rpm it takes to get that horsepower. Engines have an rpm limit they can safely run. The only difference in price building a 273 and a 318 is pistons. What is the big deal? At least you can get decent 318 pistons now.