Head gasket

[Aron Gleason]

My 440 has .020 thick head gaskets, how much would the compression drop by using .040 head gaskets?

 

[451Mopar]

Each 0.020" of head gasket is about 5cc volume.
The piston swept volume at stock bore size for a 440 is 54.97 cid (54.97 * 8 = 439.722" or 440 cid.)
Converting cid to cc is 1 cid = 16.3871 cc, so 54.97 * 16.3871 = 900.722 cc

If the volume above the piston at TDC is 100cc then Compression is (900.722+100) / 100 = 10.007:1 compression.
Adding 5cc would be (900.722+105) / 105 = 9.578:1 compression. Difference of 0.429 point of compression.

If starting with lower compression, say 110 cc above the piston = 9.188:1 compression, adding another 5cc drops compression to 8.832:1 compression.
Difference of 0.868 point of compression.

OOPs "9.188:1 - 8.832:1 = 0.356 difference (NOT 0.868!)"
4:30 in the morning, not even sure where I got that number from?

 

[62 Dart Convertible]

If starting with lower compression, say 110 cc above the piston = 9.188:1 compression, adding another 5cc drops compression to 8.832:1 compression.
Difference of 0.868 point of compression.

9.188:1 - 8.832:1 = 0.356 difference (NOT 0.868!)

 

[dvw]

Depends on your current compression ratio. If is low it’ll make very little difference. If it’s high it can make a huge difference. Adding .009” in gasket reduced my race engine from 15.45 to 15.01.
Doug

 

[451Mopar]

9.188:1 - 8.832:1 = 0.356 difference (NOT 0.868!)

Thanks for fixing that.