rocker ratio

Could you please explain rocker ratio alittle more?

Of course. With a valve train that uses a rocker valve actuation system, the lift provided by the cam doesn't always equal the lift delivered to the valve. This is achieved with the rocker. Let's say that the distance from where the cam lobe or pushrod contacts the rocker to the centre of the shaft the rocker rotates on is 30 mm. If the distance from the centre of the shaft to the point on the rocker where it contacts the valve is also 30 mm then the ratio is said to be 1:1 and the cam lift equals the valve lift.

If we now extend the end of the rocker where it contacts the valve so that it is 60 mm long then we have the effect of doubling the cam lift (i.e 5 mm cam lift would equal 10 mm valve lift). This ratio would be referred to as 2:1.

Here's a video that explains the situation - https://youtu.be/7CKH_cjUD5A?t=2m46s

Thankyou for explaining, appreciate it