ejscarfo

After consulting with my C4 brethren on crate engines, I'm fairly certain I'm going to go with an ATK short block and add my 91 118 heads and intake to that. I also plan on using a cam close to the stock specs.

Using that block and my heads, doing a quick calculation on Summit's site, the compression comes out to be roughly 10.41 :1 using a head gasket of .041 compressed thickness. Is that ratio too much for the 85's ECM to handle or should I get a thicker head gasket?

Bore: 4.040 in
Stroke: 3.48 in
Cylinder Head Volume: 58 cc
Effective Dome Volume: +6.9
Compressed Gasket Thickness: .041
Number of Cylinders: 8
Compression Ratio: 10.41 : 1

bjankuski

Redo the calculation with -6.9 cc, if the pistons are flat top design with valve reliefs then it will be a dish volume. If you are 10.25 or less you should be fine.

Kevova

It should be cam selection is a factor. Actual compression will be lower because unless you have "forced induction" cylinder will not have 100% filling. 75-80% I would expect. A fast acting cam can promote cylinder filling. Cams with a lot overlap can reduce filling.