OZ38 wrote:I think you have high lighted to me a fault I was seeing when helping a friend out pit crewing his Methanol Mechanical fuel injected Camaro drag car.Charlescrown wrote: Comparing alcohol fuel to petrol might not be a good thing. Some tuners have made the mistake of tuning up to detonation and with alcohol you will hammer the guts out of the bearings due to the rod/crank angle obtained without detonation.
I noticed the way they would set their spark timing was lock in at something like 34-38 degrees BTDC on the crank trigger device. Then they would set the fuel injection pill (return line jet) based on the EGT they got at the end of a run, fatter (rich) or thinner (lean) they would refer to it as. After seeing the engine fail one time with a ARP big end bolt letting go shortly after a rebuild by recognised race engine builder. I started to wonder if the point of peak pressure was happening a little to close to TDC. Tuning of these engines didn't seem to have the benefits of engine management that could control knock. Or so it seemed by the way these guys were playing with them & winding then locking spark advance so far forward at the high idle.
Thing is alcohol is great at resisting knock, but sure is susceptible to pre ignition.
Not to confuse with eachother. Knock is pockets of charge spontaneously combusting usually in a fast explosive burn due to enough heat energy in the charge to make it react spontaniously Heat = Heat, pressure = heat. Pre ignition is the whole charge lighting off just like spark plug would but set off way before actual spark and normally set of by hot spots like glowing electrode or carbon, its quite an explosive burn too. This is what happens when an engine runs on when no ignition is present. Eg Lada engines lol
Knock is damaging, pre igntion is usually catastrophic breaking rods, cranks and pistons.
I have read that alcohol fuel, its a good idea to run couple of numbers cooler plugs to prevent pre ignition on alcohol.