8.5:1 - Quench head engine for tow service, motor home and truck.
9.0:1 - Street engine with proper .040" quench, 200° @ .050" lift cam, iron head, sea level operation.
9.5:1 - Same as 9:1 except aluminum head used Light vehicle and no towing.
10:1 - Used and built as the 9.5:1 engine with more than 220° @ .050" lift cam.
A knock sensor retard is recommended with 10:1 engines.
12.5:1- Is the highest compression ratio suggested with unrestricted race gas engines.