Hello Ed,
I'm not 100% sure about the stiffness of 73mm- bore pistons in comparison to 77mm- pistons, both with the same wall- thickness. I would say, that, with the same wall- thickness, the smaller pistons will definately be stiffer than the 850- pistons, and so may also be less prone to distortion. I will not give a comment about if they are stiff enough for your job or not. They might be, but they may also not be. There is no guarantee. I nevertheless would say that the 850- pistions may not have been sufficiently tested in long distance tests.
Nevertheless, let me say one word about the shorter pistons. Unfortunately these are my after- thoughts:
The shorter pistons have one big advantage. They are a lot lighter and because of a smaller angle of centre- line conrod to the centre- line cylinder (at appr. half stroke) they also have a lot less normal forces (and so less friction) towards the cylinder- wall.
Yet, they also have a big disadvantage: Their guide- length is a lot shorter in comparison to the standrad-length pistons. This also means that the tendency for the longer pistons for tilting is a lot less critical, which today may lead me to a different decision if it comes to the purchse of the shorter pistons.
Jim Schmidt's pistons are longer than M.A.P's and also a lot stiffer. That's why, now I bought Jim Schmidt's. Now I have the problem, that I have to bore the small- end bush to 18mm ( and also boring the small- end in the conrod itself), which is another problem and a job for a very specialized company.
As I said, I have done a lot of research about my M.A.P 850- pistones. And these have definately failed, because of more and more tilting and the resulting distortion. The more distortion, the more tilting, which finally resulted in more and more oil burning.
If you wish I can send you the complete story about my 850- pistons.
Best Regards
Klaus
