fdracer

why does advancing timing make more power considering the intake charge hasn't been fully compressed. if tdc is where full compression takes place wouldn't having ignition just a few degress btdc make the most power? wouldn't advancing timing beyond this effectively lower cr? sorry if this is a stupid question.

Gearhead

iTrader: (1)

Advancing the timing causes the "fire" to start sooner. Firing sooner increases the pressure in the combustion chamber sooner causing higher pressures right after TDC. This higher pressure makes more torque. There is a limit, however, to how much advance you can run. If it's too early, the increasing pressure of the "fire" added to the increasing pressure of the compression stroke will cause an explosion (detonation). The fire caused by the spark plug is a gradual (in relative terms) increase in pressure due to flame propegation (sp?) and other factors. It is considered a controlled fire. Detonation, on the other hand, is spontaneous combustion of the intake charge that is more of an explosion with rapid increase in pressure. If too early it will actually try to rotate the assembly in the other direction. Good bye apex seals.
Don.

fdracer

i know that, what i'm asking though is why it would cause higher combustion pressures if you ignite sooner. it seems that advancing timing indefinitely creates more and more hp. the only determining factor as to when to set timing is to advance timing to the limit of detonation. but, shouldn't there be a point where advancing timing actually makes you lose power? the sooner you fire btdc the less the intake has had time to compress. the earlier you ignite it in it's compression stroke the more you've lowered the engine's dynamic cr.