This ended up being a surprising test. The idea was to compare actual valve motion of a stock head (ended up being ProMaxx) to the same head with the rocker shaft relocated to a 'corrected' mid-lift position. Rocker arm was PRW stainless 1.6 ratio. See the first two pictures for the set-up. A solid (epoxy filled) lifter was used against a cam rotated such that the lifter was on base circle. Gage blocks were placed between the cam and the lifter to simulate valve lift. Actual valve lift was recorded from a digital indicator placed on top of the rocker roller tip.
Conventional thinking says that by raising the rocker shaft and moving it away from the valve a more proper geometry will result which will give the following benefits: Less roller tip sweep across the top of the valve, increased total valve lift, increased acceleration of the valve off the seat, decreased velocity of the valve over the nose. Interesting which of those proved correct.
The yellow paper shows the results of tests. The 'Valve Lift' column shows the actual valve lift at each cam lift increment. The rocker ratio is cumulative rocker ratio which is the total valve lift divided by the total cam lift, line by line. The 'Relative Velocity' column is similar, except it is the change in valve lift divided by the change in cam lift. For instance, between 0.100 and 0.150 cam lift (a change of 0.050") on the stock head, the valve moved from 0.161 to 0.241 (a change of 0.080"). 0.080 divided by 0.050 = 1.60. This number gives a 'relative velocity' number that tells how much the valve moved during that lift increment. It's more like an instantaneous velocity compared to the rocker ratio which is like an overall average velocity. That number is useful for comparing velocity of the valve off the seat or at any other location in the lift cycle.
The results are quite surprising. I did this test over and over again over the course of 3 days to make sure it was correct. I didn't understand what was going on until I added the cam, lifter and pushrod to the drawings. As can be seen from the last two drawings, relocating the rocker shaft away from the valve increased the misalignment of the pushrod and lifter from an average of 14.71 deg to 15.45 deg. This negatively affects the geometry on the pushrod side of the rocker so much that the valve motion suffers.
As can be seen there are some discrepancies between the actual measured data on the yellow paper and on the 'predicted' numbers from the CAD drawn papers. For instance, the CAD drawing predicts a valve lift of 0.670" at 0.430" of cam lift. Actual measured valve lift was 0.678". For the 'Corrected' head the CAD drawing predicted 0.668" and the actual measured value was 0.665". The point of the CAD drawings is not so much to come up with the exact same numbers as measured as it is to explain why the relocated shaft gave surprising results.
The geometry on the valve side of the rocker arm is a little less complex than the pushrod side. Fixing the geometry on one side alone can lead to unforeseen problems on the other side.
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