89mm
I was replying to the post immediately before the one you refer to. Demojob had refered to some 79mm pistons that he had used in his engine, hence the mathematics.

When i asked "did i get that right?', i meant, would "would 1608cc put you over the limit & disqualify you from the class you wish to race in?'
According to B310GX, it would not. Woohoo!
Chris