BBC piston clearance

I am getting ready to run a new rotating assembly in my BBC 1471 hi helix 29% over Dart headed 555ci altered with a p/g. Before I was at zero deck with a .060 copper headgasket. We over-reved the motor a couple times and several pistons hit the heads. This lead to a rod bearing failure and then to a broken rod flying out of the pan. How much clearance do I need? Should we run the piston in the hole some? Was going to shoot for 11 3/4 to 12 cr.

thanks

 

just an opinion.

The flame travel tends to be so poor in a big block with a full dome that it is usually more powerfull to give a little compression up in exchange for more room around the chamber area. Asuming you are running an aluminum rod? You should have minimum .080 quench and .100 between the dome and the rest of the chamber area. The dome should have any angles removed and have a smooth contour and sometimes may even be usefull depending on your piston design to have a flame ditch carbided into the top center of the piston.

good luck
Thomas Mohan

 

11.75-12 is a little steeper than I've tried with a 14 but given the oppurtunity I would try it.
I ran as much as 9200 RPM last year, normally 8000-8500 with 55-60 thous clearence.
I would run 55-60 quench, lessen the dome height and turn the blower up.

 

This was my experience too (28 years ago) w/ a BBC TAD.
DC