Thread: 4.6 Litre Compression Ratio.

I think its a bit silly to be building a HC engine and use composite,, MLS would be better,, even then you get a choice of two thicknesses 40 and 20 thou. Obviously studs and close to 90 ftlbs. Trust me when I say composites and TTY and 70lb will fail. And have been doing so ( on standard comp motors! ) since LR bought the engine...

isnt there a calc for area around the piston to the compression ring depth?
I built mine a few years ago now,, all that info should be IN here somewhere...

G`day ,

if your talking LR pistons the deck height is likely +0.020 measured and the Pedro bit above the comp ring is likely +1cc not certain that was measured but each engine will be likely be different , i seem to remember 4.0 piston tops hold fewer cc than 4.6 .
I have written done 9.37:1 for factory 4.6 but years ago now and block stamps don`t always relate well to net info .

In my motor the piston is 0.040” down the bore. So, with composite gaskets the compression ratio is very close to 10:1.

I put No. 1 piston in today, left hand head, an old composite head gasket, camshaft, and the rocker gear. Lifter preload was around 0.050”. I bought some valve springs which can go to around 0.500” lift.

The camshaft I have has 0.450” lift on the intake and 0.474” lift on the exhaust. Used 2 old lifters full of oil in the No. 1 cylinder position. Degreed camshaft with the ICL figures. With the exhaust valve at full lift the valve retainer contacted the valve stem seal and pushed it down about 0.020”, the spring still had a bit more it could go before coil bind.

Tomorrow I am going to put some plasticine on the piston and see how close the valves are getting to the piston. I have read you need at least 0.060” clearance, I think the exhaust will be closer than that.