Here is a sim run from GP125 with 36mm carb.The 24mm carb high velocity and area reduction showed little difference with RV changes.
The stock timing for this setup was 140-88 a very normal racing engine duration spec.
I then symmetrically retarded the valve to 158-70.
Then after seeing the result of closing early only with a servo setup on an old BigHorn experiment,I symmetrically reduced the timing 10* each side to 130-70.
The sim showed the basic effects, but cannot show the proven issue that when opening any earlier than 140 the carburation becomes impossibly finicky to tune.
Thus the symmetrical retard I believe would have a small effect on the power spread - hamstrung by the bad carburation in the midrange.
But the symmetrical reduction of both sides of the port would have alot more positive effect, with better throttle response as well as an improvement from the retarded closing point.
This can be achieved with a setup like a pair of scissors oriented vertically, sweeping open and closed symmetrically across the port.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
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