TR6 Compression Ratio

Compression = Volume piston down (combustion chamber + head gasket+ deck + displacement)

Ratio volume piston up (combustion chamber + head gasket + deck)

This chart is based on a compressed head gasket thickness of 0.035” which equals 4.0 cc.

The head thickness required to achieve a given volume is based on new valves and seats and a stock combustion chamber. Valves that are recessed into the head or modification of the combustion chamber will increase the volume and lower the compression ratio.

Every 0.010” of valve recess into the head adds to the combustion chamber volume as follows:

Intake valve adds 0.26 cc,

Early exhaust valve (1.260” dia) adds 0.20 cc,

Late exhaust valve (1.197” dia) adds 0.16 cc.

Every 0.010” removed from the head thickness reduces the combustion chamber volume 1.03 cc.

This chart is based on “0” deck clearance (pistons flush with the top of the block). Every 0.010” that the piston is below the deck adds approx. 1.1 cc. To achieve a given compression ratio with pistons that are 0.010 below deck cut an extra 0.010 from the head. This will reduce the combustion chamber volume approximately the same amount that was added by the deck height.

Displacement volume per cylinder is as follows:

Std bore – 416.33 cc

0.020” over – 421.74 cc

0.030” over – 424.60 cc

0.040” over – 427.50 cc

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