Speed and horsepower don’t make very good bedfellows. While it’s true more power will increase speed, the trade-off is grossly disproportionate. Forget the math—it takes an exponential amount of power to improve cruise enough to notice. Ask Lyle Shelton, owner of Rare Bear, the Unlimited Class racing F8F Bearcat that’s won the Reno event a half-dozen times. Shelton runs a Wright R3350 engine pumped up to an estimated 4,000 hp in place of the standard P&W R2800, rated for 2,100 hp. Shelton learned early on that, despite the huge horsepower increase, his fighter would need major aerodynamic improvements to become a consistent winner.
Unfortunately, adding power puts you into a vicious cycle. More power means higher fuel burn, which usually means increased fuel capacity and less payload, so you need to increase gross to maintain payload. Higher gross means less speed, so you need to increase power again, which means higher fuel burn…you get the idea.