[email protected], about 10.2:1, with a 3.31 stroke... Yeah, I'd think in Park I'd expect 10" or less. In gear that might drop to 5-6. Depending on the fuel and setup, I'd think it should be pinging long before it kicks back. But you have a huge chamber and a domed piston... It takes a while for the flame to propogate and build pressure and that short stroke means the piston isnt at TDC for very long.