GS1100 comp

[Dink]

the easy way to work out C.R. is to remove one plug (lets say #1 for ease) roll the crank untill it is at TDC pour petrol or something similar into in from a measured container (using Paul example of a 10:1 100cc motor) it should take 25mls now turn the crank until it is at the bottom of its stroke and refill it, divide the first measurement into the second and you have your C.R.
BTW Pauls example #1 is incorrect C.R. is always total volume divided by compressed volume.
Dink

[SqDancerLynn1]

Here in the US we have 91 octane maybe 92 unless you want to buy expensive racing gas

[saaz]

Just be aware that when people talk about octane rating the country matters. In Australia, UK and I think Europe RON is used, which gives a rating higher for the same fuel than the Octane method of the US. They are not strickly comparable. This can matter when people talk about what fuel thay can use.

RON Reaserch Octane Number.

MON Motor Octane Number. This value is determined in a different way. It is often considered to be more sensitve to changes in operating conditions and their effect on the engine than RON.

AKI Anti-Knock Index. This is the number that is posted on the gas pump in the USA as "Octane". It is derived as (RON + MON)/2 In other words, an average of RON and MON values.

RON is typically 8 to 10 points higher than MON. Therefor, the average is typically 4 to 5 points above MON and 4 to 5 poins lower than RON. Thus, a requirement for 95 RON gasoline should be met by 91 "octane" fuel in the US.