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On 24 Sep 2003 at 7:35, Jens Vagelpohl wrote: > If I remember correctly the balance of forces acting on the > piston/connecting rod/crank changes and the force needed to pull the > piston down on the intake stroke gets much higher, or something like > that. It's been a while :) I'm sure you're right. I suspect these forces go as RPM squared, but we're only talking brief short-term excursions into all those realms. OTOH, if you look at the overall picture, there are 2 groups of forces acting on the crank, the simple centrifugal one and the pressure from the head of the piston. On the downstroke these work against one another, minimizing the resultant force, while on the upstroke they work in concert. So, while the downstroke loads would be minimized under load, the upstroke loads are maximized. Actually we probably have to separate the downstroke intake load from the downstroke combustion load. The latter probably passes thru a minimum and increases again. The crossover point would change with RPM. -- Jim Adney jadney@vwtype3.org Madison, WI 53711-3054 USA ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org