picked up a set of heads for the 398w. 58cc chambers werent ideal but the deal was too good to pass up on. engine builder said id be 11:1 on 64cc heads. so im figuring 11:5 this way. I understand that's static compression and probably calculated a little higher than it actually is. Also figure dynamic compression might be in the safe range. I just have no interest in a strictly race gas build and a thicker gasket causes more problems than trying to use it to combat high CR will help 5.9 truck rods rpm 3.850 crank xe284h camshaft AFR 2o5cc 58cc chamber 70cc raised .125 exhaust port heads #1450 .060 hypers flat tops with deep reliefs 1.7rr 1 3/4 longtubes 750 carb I know on the LSx cars, you can run 11.8:1 on pump gas with a good tune and this being an iron block aluminum head combo i know im good up to around 11:1. best bet is to assemble it and see if it has any spark knock on 93 oct. Just want to hear from some guys "in the know" more than i am in case i need to re-evaluate the combo.