Originally Posted by Delta5

Hi guys...the real problem here is that you are getting "hot spots" in the cylinder heads! It comes from not having rnoug block pressure at idle. In the old days we used a 5/8s hole in a restriction plate in place of a thermostat to get the 25 psi needed to coo, under rce conditions, in the 510 cid Reynolds (all aluminum with iron plated pistons, no sleeves) the 526 cid spacer motors and the L-88s and the original ZL-1s as without the restriction air pockets get real hot and boil small amounts of water all through the heads and the steam gets more of it boiling...hes the answer is mor water being pumped in and either a thermostat or a restriction plate for the size engine you have...there used to be a division of Chevrolet Engineering that always had these answers??? Hope this helps cool her dwon might not need another prop just more rpm!