They are standard 2t pistons. Flycut with valve reliefs
to suit 2t-g. It was a long time ago, but they were purchaed
by accident (instead of 3t) and flycut on the understanding they were 3t pistons.
I cant remember, but i think the 8.4:1 pistons had a dish or
half a side missing (aside from the valve reliefs) Where as
these pistons are somewhat domed. (see pic)
If the head cc's are the same between 2t and 2t-g then
they would be lower than 2t std compression. If the head
is smaller than a 2t then i guess higher. If there is a pic somewhere of an 8.4 piston i can compare to some degree at least if it is going to be higher or lower. It was just a while ago
now so i don't remember.