piston ovality

"how to calculate piston ovality and what is the formulae."

Measure maximum and minimum diameter and compute the ratio.

Single - Doulble Ovality

This link will give you the formulas for single, double, and triple ovality.

Blink the link you gave can not be reached. Could you please upload it if you have it.

it's my understanding that the purpose of the ovality is for the piston to expand to roundness as it achieves operating temperature

That's what I think. However, I have seen competition pistons, I can't think of the make right now; but they are the really slimline ones, that are supposed to be as near perfectly round as they can get them. Of course, they don't have a great lifespan....

Room for expansion is accomodated by the ring gap. The primary reason pistons are oval is that because there is a small amount of flip flop slop in the motion around the piston pin. An oval shape tilted in the bore will present a circular aspect to the top of the cylinder. Thus, you will have a more circular face presented to the cylinder forces for the majority of time during both compression and power strokes.

When a motor is severely overheated the pistons will lose their oval shape and the subsequent loss in power is easily detected on the dyno. In this case the opposite effect occurs. During compression and power stroked the forces see an oval shape in the bore and the increased leakege results in less power.

thanx for the response ya its true thge ovality is the difference between the major axis and the minor axis and it is provided to attain the circular shape when the piston is their inside the engine.but i want to get the details about the double positive and double negative ovality and can some body make this clear with details along with some data on symmetrical profile and un symmetrical profile.