Originally Posted by
rd415
I've been thinking about this octane business and extra performance - technically the car is tuned to the octane and therefore a higher octane will only produce a lower power output. Modern computer electronics "self learn" from the sensor inputs, but even then it doesn't happen instantly.
There are plenty of bonifide cases to prove the point - one was the Bathurst 12 hour and an EVO driven by one Eric Bana. It is pretty well documented that he was very slow in practice, erasing the memory fom the computer and going out again and thrashing the EVO put his times up near the front. There are plenty of other recorded cases to prove this.
If you look at the actual technicality of the fuel the octane is it's anti-knock value which is actually the time period it takes the fuel to burn. The knock is caused by the fuel prematurely burning by either compression or a mechanical fault. The timing in an engine is set up so that maximum pressure occurs in the cylinder around 18 degrees after top dead centre. The fast the rpm the sooner the burning has to commence. If you use your common sense you can clearly see that a higher octane fuel burns much faster so therefore the ignition requires to be advanced considerably to finish burning at 18 degrees ATDC. Even modern computers take time to learn this advance, they won't do it instantly because the computer has to read every sensor to ensure correctness. This includes things like turning the Air Conditioning off & on, steering from full lock to lock, brakes, WOT (wide open throttle) sppeed ane temp sensors etc. All the inputs have to be correct to alter advance curve, let alone altering the amount of advance.
The answer and conclusion is that higher octane fuel WILL NOT increase performance without other modifications, the fact is that in most cases it actually reduces performance as the fuel doesn't finish burning until after the piston has gone on power stroke and therefore lowers the combustion pressure and power output.
Sorry for being a bit long-winded but I have tried to explain the mechanics of the fuel burn - I just hope it is easy enough to understand.
Footnote:-
1. Detonation is caused by the fuel igniting under temperature and compression, two flame fronts collide (one from heat and other from normal spark ignition - usual result is a hole in the piston (instant)
2. Pre-ignition is caused by something other than the spark plug igniting the fuel - pinking (commonly called pinging) - usual result of continued pinging is a hole in piston, but this time the piston melts, unlike detonation which pops a clean hole through piston.