Analysis of F1 engine performance in 2009 | James Allen on F1 - The official website
Most teams reached the conclusion, based on acoustic analysis and GPS, that the spread of engine power from the best to the worst engines was less than 2.5% this year. This means that, if the Mercedes is believed to have had 755hp, the least powerful engine was 18hp down, which is worth just under 3/10ths of a second per lap.