rfox is right.To put it in plain talk a bigger motor has a bigger cylinder bore and usually bigger valves.A cam that causes a 283 to breathe deep,due to lift,duration and valve opening and closing points,won't fill the 454 equally or the same volumetric efficiency won't be met due to the larger motor's bore & valve size.Of course there are many variables to deal with when talking about optimum cam timing for any given motor but it's all about what the cam will do to 'effeciently' fill the chambers.