Hitchcocks Forum

Hi,

I would like to increase the compression ration on my 535 EFI by installing a thinner gasket or skimming the head. Has anybody done this yet? How far can I take it without damaging the engine?
(When I installed the 535 piston I forgot to check on the clearance between the piston and valves - anybody knows?)

Many Thanks

Roeland

I am running a 535 carb - converted EFI and I would be careful going any higher - Std compression on the EFI is approx 9.0 :1 and the 535 piston looks to be about the same compression ratio, I have not fully run mine in yet but its showed signs of detonation on normal fuel - I am running on Super unleaded now and it seems better which indicates its pretty close.

Arthur, I thought the standard compression ratio was 8.5:1? To make it 9:1 I would need to remove about 0.6 mm from the head. I was hoping to maybe go as far as 9.5:1, nothing higher. I'm still running on the standard unleaded petrol and experience only the occasional backfire or rumbling sound, mostly on de-acceleration. I kept the fuel injection, but installed a powercommander 5 to be able to tune the mixture. Regards