i would say that is accurate to a point. It isnt exactly a straight line comparison, as there comes a speed where it takes much more than 15hp to pick up 1mph. It might only need 15hp at 70mph to gain 1mph, but might need 50hp to get that same 1mph at 115mph.

Absolutely true!, It applies to 1/4 mile drags to. The faster you go, the more hp it takes to gain that extra mph. General rule of thumb (on the water) is that it's about 1 mph gain per 15 hp....to a certain point. Weight also plays a big factor in that calculation also.

Hi there,
I've done six years and 150-200 hours on the motor you're talking about after it had already run 200+ from new. Weiand 177 at 5 lbs of boost. Motor has run flawlessly. Boat went from 66mph to 75mph (20' Cigarette, Bravo). Fully willing to admit that I've been lucky, but it's done the hours.
Good luck,
Y