A 410 inch engine at 7500 rpm would need a 14x4 air filter. A 500 inch engine at 7500 rpm needs a 14x5 filter. I've used 14x5 and 14x6 filters on the dyno with 500 inches and a 1250 Dominator and there is no restriction. But it is hard to fit that large of a filter under a hood unless you use an extra tall 6 pack style.