For comparisons sake, a 2003 WRX generates approximately 155 wheel hp when tested under similar conditions. Assuming the WRX’s horsepower is rated properly by Subaru, we run into a little problem. If the 227HP WRX puts 155 horsepower to the ground, why does the 271HP EVO only put down 180 wheel horsepower? Shouldn’t it be closer to 200 wheel hp considering the factory horsepower rating. Eager to find the answer to our questioned, we turned our attention to the fuel we used for our testing. Operating out of the lovely state of California, the highest octane fuel available is 91 octane. To see how the EVO would react to the higher octane fuel available in most of states, we concocted some 93 octane fuel by mixing our 91 octane fuel with an appropriate amount of 100 race gas. The results were astonishing: A substantial 8-10 wheel hp gain after an ECU rest and several learning runs.