18 ec300 compression ratio

[taylor146]

Hi all,
Been having some troubles getting the jetting right since my cdi remap, the engine tends to detonate after periods of WOT, with racing idle. So checked the combustion chamber volume with a 50ml burette at tdc which measured 22.8 ml. Used a compression calculator and worked it out to be 13.85: 1. I'm thinking that this is too high, the squish is 1.9 at the edge tapering to 3.2 . What comp ratio are people using who have had head work done on the 18 300.
Thanks Darren

 

[(F5)]

To account for spark plug volume measure 3 threads up. Also measure 3 times until you get your eye in. Best to prop the front wheel up so upright cylinder.
Your local gas choices will influence what is max. On the face that does sound high.

 

[taylor146]

Hi F5,
Yeah did like you say, removed rear wheel got cylinder level with front propped up, greased the edge of the piston, wiped it clean to seal the rings. Measured to the top of the plug hole 25.2 then removed the head and measured the plug hole 2.5 ml , plug was 0.1ml so in total 22.8. why would gasgas design a head with massive squish and seemingly very high comp.? Could the port/ exhaust design warrant this comp ratio , had an older gasser with a S3 head with black high comp insert that was 13:1.