421 Compression Calculator

Simply fill in the form below to calculate your compression ratio.

Bore (diameter)

Stroke

Cylinder Head Volume

Effective Dome Volume(-) dome, (+) dish

Deck Clearance

Compressed Gasket Thickness.040 is standard thickness

Number of Cylinders

421 Block — Displacement Reference

Over	Bore	4.00" stroke	4.21" stroke	4.25" stroke	4.50" stroke
Stock	4.093	421	443	447	474
+.030	4.123	427	450	454	481
+.035	4.128	428	451	455	482
+.040	4.133	429	452	456	483
+.060	4.153	433	456	461	488
+.065	4.158	435	457	462	489