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516 might spec at 74cc but unless it's already been milled they typically measure 84cc....

And that 8.5 C/R estimate is pretty optimistic as well...

i just milled my 906 heads 40 and there are now 74cc and those are open chambers, 516 are same chamber as 915 closed there 74-5 ccs now unmilled.



Someone must have milled those 906's then because out of the factory it will usually measure 90 cc. typically every .005 is 1 cc so with .040 off you only pulled out 8cc . the specs you are quoting for the 915 is NHRA I'm guessing which is alot smaller than ACTUAL .

As far as everyone telling him to change to a taller CH piston with it the way it is another post brought up a valid point ... CYLINDER RIDGE , unless he removes the ridge he will BREAK the new rings and from the sounds of it , NO ENGINE HOIST and he says he has NO CAR the block isn't coming out of whatever it's in anytime soon .

Buy hemigod's 516's and thats the best you will do with the constraints you have to work around for the short term fix .