There are some circles that show increased power can improve gas mileage … if and only if the driver continues to drive the same as before without taking advantage of the additional power. For instance, a Jeep Wrangler with an upgraded engine will be able to handle itself under road conditions without as much energy as before. This all goes for naught, of course, because people with Wranglers will use that extra power to climb a bigger hill. Same with sports cars – the increased power just makes the driver burn that much more going faster, etc.

It really all depends on where that power came from. Improvements to the engine? Better combustion timing, fuel / air ratios, etc? That can mean more fuel economy. More cylinders to burn more? Well … yeah, that just fucks everything up for more VROOM VROOM. More horsepower means bigger spinners.