Math
What do the letters & numbers stand for ?
Ok, off my memory so remember that...
Rk is the core roughness value. It gives you the idea of how rough (or fine) the finish is, but without the other numbers it doesn’t mean too much. I mean it’s important but you can’t really define what you have without the rest of the numbers.
Rpk is the distance from the mean on the Y axis to the highest peak.
Rvk is the distance from the mean on the Y axis to the deepest valley.
Ra is the arithmetic sum of the absolute values of the peaks and valleys over the length of the measurement.
Keep in mind the mean for RPk isn’t the same mean as Rvk, because the mean line is related to the average of the distance across the peaks and the Rpk mean is the average of the distance of the valleys.
Now, to evaluate all that math requires knowing what rings you have, piston speed, the hardness of the block, fuel used, NA or power adder...and probably some other things I’m forgetting.
The best thing to do is call your ring manufacturer and tell them what you are doing and they will tell you what the finish SHOULD be.
Hitting those numbers can be a bear if you haven’t honed that particular brand of block or sleeve before or if the manufacturer changes the hardness of the block or sleeve. Compacted Graphite blocks do not hone the same as the run of the mill SBC block, which happen to be the softest blocks (BY FAR) of the big 3, with Chrysler being the hardest and Ford not far behind.
Any aftermarket race block should be harder than an OE block. That changes the finish required.
And I can say after watching the new hone work that it’s near impossible to get the numbers correct on a non CNC machine and especially with vitrified abrasives.
The profilometer doesn’t lie. I also forgot even the engine oil used can change the surface finish.
