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Originally Posted by osgood  Simon I will stand corrected on this but I don't think you will find any difference in the combustion chambers, the 4:6 heads are pretty much the same as the 3:5, 3:9. 4:00 & 4:2 with the same size valves,The CR is controlled by the piston dish in comparison with the bore size, I have recently fitted 8:4.1 pistons in my 4:6 ready for supercharging.There is however a bit more space within the inlet and exhaust ports but the exits & outlets are the same size. Just fit your old ignition system (Dizzy coil etc)and all will be okay. As said inlet manifold will also fit but require a bigger carb W.H.Y. I have built many Rover engines of all sizes and most all parts interchange Osgood |
If you use the 3.5 heads on the 4.6 block you should use the tin gasket otherwise you'll lose 05:1 off your cr. Rover took about 20thou off the head to reduce the combustion chamber size to compensate for the thicker composite gasket.
Kev