Quote:
Originally Posted by Dominik
If you order a new cam, surely you can get the lift and duration you desire without looking into an increased rocker ratio.
Dom
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Yes you can get the same duration and lift, but think about the ramp rate. Lets assume you have two setups where you have the exact same lift and duration at the valve only one is using a 1.6 ratio rocker and the other is a 1.7 ratio. On a flat tappet the lobe can only increase at a cetain rate or the edge of the lifter starts to dig into the lobe. So the ramp rate is limited. The higher ratio rocker will give you more lift, so the valve is opened more at every point on the ramps, even though you have the same total lift and duration. This gives you more area under the curve, so if you integrate the open valve postion the higher ratio rocker had the valve open more over time.
Now if you are using a roller lifter cam, I do not know if the ramp rate is limited by lobe and lifter geometry or if the ramp rate is limited by valve train wear or what ever it may be. If it is still in the lobe lifter area then the higher ratio rocker may still make since. If it is limited by valve train wear then it would be a bad idea.