Because an engine may be borderline in regards to the compression ratio when it comes to ignition timing or fuel octane requirements, it’s important that all values used in the compression ratio calculation be as accurate as possible. This includes the head gasket volume which many times isn’t stated on the package or in any reference material. For a conventional or mainstream engine where the fire ring in the head gasket is perfectly round, the hole size in the gasket can be measured and the volume calculated appropriately. But the Ford Y-Block has an irregular shape to the fire ring seal which throws special nuances into the measuring of this volume. But there’s no need for guess work when it comes to obtaining this volume value as it can be derived by doing some simple measurements on an existing head gasket and then performing a little bit of math.

Once you have a known length around the head gaskets’ sealing ring and the compressed gasket thickness, there is now enough information to do the actual calculation for the head gasket volume.

Here’s the basic formula:
((sealing ring distance in inches / 3.1416) squared) X (compressed gasket thickness in thousandts of inches) X (12.87) = head gasket volume cc’s.

Here’s an example where a particular head gasket measured out at 13.0” for the combustion chamber seal and was 0.041” thick.
(13” / 3.1416)² X (0.041”) X (12.87) = 9.04cc

Here are some known head gasket values for the Ford Y-Block engine.

Best Gasket for regular bores                12.91” X 0.046” = 10.00cc
Best Gasket #572B (3.937” bore)         12.99” X 0.046” = 10.12cc
Best Gasket (4.030” bore)                    13.35” X 0.046” = 10.69cc
Fel Pro #7999PT (Permatorq Blue)      12.95” X 0.044” = 9.62cc
Fel Pro Multi-Layer (old design)          12.60” X 0.039” = 8.07cc
Fitz 3 layer (metal,comp,metal)           12.80” X 0.048” = 10.25cc
Fitz 2 layer (metal,composition)          12.80” X 0.050” = 10.67cc
Fitzgerald #0645 (metal/metal)          12.76” X 0.031” = 6.58cc (40+ yrs old)
Flatout #FOG9123.5 (3.830” bore)      12.64” X 0.040” = 8.33cc (copper)
Ford steel shim C1AE-6051-B               12.68” X 0.025” = 5.24cc
Ford steel shim C3TE-6051-E               12.68” X 0.026” = 5.45cc
McCord p/n Mc6392M                           12.79” X 0.048” = 10.24cc
ROL Gaskets #HG32120                      12.79” X 0.045” = 9.61cc
SCE copper                                         12.99” X 0.042” = 9.24cc
Victor #1176TC composition                12.95” X 0.043” = 9.40cc
Victor #1176BS steel shim                  12.68” X 0.025” = 5.24cc

This information is just one more tool in guaranteeing the accuracy of the static compression ratio check on a given engine. Special thanks goes to Michael Henaults for providing some of the head gaskets for measuring.

Until next time, happy Y motoring. Ted Eaton.

Click on picture for a larger image.

Originally published in the Y-Block Magazine, Nov-Dec 2010 issue, Issue #102, Vol 18, No.1