[.041 Safety Wire]

AOA,

I noticed in one of your earlier threads you stated that higher octane ratings tranlated into more horsepower, please explain this statement. I thought higher octane ratings just reduced the chances of PING and untimately the possibility of detonation of the fuel air mixture.

Short answer increasing the octane raises the level at which a engine will ping, thus higher octane enables you to run at higher manafold pressuses before the engine pings, thus more power. Put another way if you tried to increase the manafold pressure on lower octane fule, it would start pinging sooner and thus less power. A ping in a low compression engine like our cars today results in an anoying sound.. where as with these high performace engines the ping sound can be and typcailly is followed by the sound of the engine comming apart

So I guess when the AAC started using the higher octane fuels they had to install high compression pistons and retime the powerplant and tune the supercharger controls to take advantage of the higher octane fuel. Because if the engines were not tweaked the higher octane rating could result in a lower power output since it is slower burning than the lower octanes and only is effective when the compression ratio is increased and timing changed. Manifold pressure is controlled by the throttle plate and if the manufacturer recommmends a miximum boost of lets say 65" Hg for three minutes then no matter what the octane rating of the fuel you should only pull the 65".

Here is an explanation found on line that is pretty accurate.

Many high-performance engines are designed to operate with a high maximum compression, and thus demand high-octane premium gasoline. A common misconception is that power output or fuel mileage can be improved by burning higher octane fuel than a particular engine was designed for. The power output of an engine depends in part on the energy density of its fuel, but similar fuels with different octane ratings have similar density. Since switching to a higher octane fuel does not add any more hydrocarbon content or oxygen, the engine cannot produce more power.

BTW PING and detonation are two different things PING will not necessarily destroy a powerplant whereas detonation will, think of PING as having the ignition timing too far advanced so the mixture ignites before the maximum compression is reached where as detonation is an uncontrolled explosion of the fuel/air mixture rather than a controlled burn. As this controlled burn starts at two different areas in the combustion chamber the flame fronts should meet as the piston arrives at TDC with maximum pressure occuring at some point after TDC.

A good read for gasheads: http://www.jcmmachine.com/PDF%20files/J ... %20ch3.pdf