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Piston acceleration (was interferance etc)

Well, I pulled some references...

According to the Bosch handbook, the inertia force is proportional to 
N^2 * (cos(alpha) + lambda * cos(2*alpha))
where N is RPM and alpha is crank angle (TDC is 0),
lambda is stroke/(2*rod length).

cos(x) is at a maximum (1) for x = 0 and minimum (-1) for x = 180 

This gives acceleration proportional to

N^2 * (1 + lambda) at TDC
N^2 * (1 - lambda) at BDC

The magnitude is greatest at TDC.

This is also covered in Corky Bell's book in the first few pages.

"Internal Combustion Engine Fndamentals" by John B Heywood
has a formula for velocity and differentiating it for acceleration,
I got:

2 * PI^2 * N^2 * stroke (1 +/- lambda)

Seems consistent.

It's notable that the force on the con rods increases with RPM squared,
so think twice before removing those rev limiters...