Hello. I'm putting the 117 5.6-litre V8 from a 1989 560SEL in my 1971 280SE (108). The 108 has LPG injection and I plan to run the 560 engine on LPG too. In order to take advantage of the high octane of gas, I want to raise the CR as much as possible. Does anyone know what the maximum amount of material is that I can skim off the heads before I run the risk of valves hitting pistons? What's the official Merc figure? And does anyone know how much this will throw the cam timing by?

One last thing - what's the maximum warpage allowed on a 560 head? Mine are currently 3thou out over their length. Is this accepatable according to the manual? I just want to know in case there isn't scope for getting much of a CR rise through head skimming. If that's the case I won't bother – if 3thou is okay.

Thanks in advance for your suggestions.