Originally Posted by paul386
There are so many things at play here that it would be super difficult to actually determine what is causing the power change. In the United States of course, we all have to subsidize the farmers and burn low energy / high pollution / high price ethanol.
The test, here in the UK, was switching fuel only. Can't see what else is coming into play except the fuel itself, and the ECU adapting to the knock rate. OK, the fuel additive package could be different, as it often is across brands, but the HP change is from switching fuel and octane rating. All fuels would have been to the same British Standard.
One of our tuning companies (Thorney MotorSport) also ran some extensive dyno tests on different fuels. A tuned BMW M3 CSL showed a 40HP gain running on RON 99, compared to the standard RON 95 fuel. Other less tuned engines (with knock control) also showed consistent improvements in HP, as the octane rating was increased.