Well Some dude awhile back Chuck Eundo or something like that, built my dads motor, my dad sent him steel crank and stuff, he got back a cast iron one, and he didnt bore it right and piston rings froze to pistons. It lasted a remarkably 2 races and we went to nationals in South Carolina and it lasted like 4 races. It would build up compression and fire and than if u held the gas half way the rpms would go up and down and it would pop, We unscrewed all the rockers and put air into the cylinders every single one came up through the intake.