Rover V8 Head Gaskets and Fixings
*Composite head gaskets are thicker than tin gaskets. When fitted to 3.5, 3.9 and 4.2 engines with 3 rows of cylinder head bolts (and 34-36cc combustion chamber heads), composite head gaskets will lower the engine's compression ratio. This means they are ideal for correcting compression ratio when head/block faces have been skimmed on these engines.
Later 3.9, 4.2, 4.0 and 4.6 engines with 2 rows of cylinder head bolts have smaller combustion chambers (28cc) and composite head gaskets as standard. Using tin head gaskets on these engines will result in a higher than standard compression ratio - ok if that’s what is intended, but undesirable otherwise.
Approximate gasket thicknesses are as follows:
Standard (tin) gaskets 0.5mm
Composite gaskets 1.2mm
Typical effect on compression ratio:
Standard (tin) gaskets 3cc
Composite gaskets 10cc