SlowLane wrote: idle curiousity).
'idle curiosity' nice one !!
SlowLane wrote: idle curiousity).
That is not it.SlowLane wrote: Here's my hypothesis: when the timing is set to 7.5 degrees BTDC, the combustion impulse is stronger than when it is set to 5 degrees ATDC. The engine is more "eager" at the more advanced timing, and so requires more restraint (via the restriction imposed by the idle speed screw) to stay down at the prescribed idle speed. Since the volume being moved by the air pump is (more or less) equal for the two ignition settings, the increased restriction at the more advanced setting results in a higher vacuum.
Okay, I'm going to have to call you on this one.Amskeptic wrote:the exhaust pulses are stronger and stop the intake scavenge at overlap.
A retarded spark moves the entire combustion event towards the exhaust valve openingSlowLane wrote:Okay, I'm going to have to call you on this one.Amskeptic wrote:the exhaust pulses are stronger and stop the intake scavenge at overlap.
Firstly, it would seem to me that a stronger exhaust pulse would result in better scavanging, since it's the velocity and inertia of the exiting exhaust gasses which draw in the initial intake charge. More energetic egress, more eager ingress.
Secondly, how exactly does retarded timing make for a stronger exhaust pulse? Wouldn't the strength of the exhaust pulse for one cylinder depend on the characteristics of the power stroke in the following cylinder? And wouldn't the power stroke have more authority with advanced timing than with retarded?
I dunno, maybe I'm the one who's retarded here, but something ain't adding up.