I understand what you are trying to say but I'm having trouble seeing how you ended up at .0005". It's too bad that stuff like this can't be expressed with a formula.
Mr. Riggs,
Sorry for the garbaled explanation, but I'm a conceptual thinker, and formulas don't make much sense to me. I understand trig as a concept and not a formula. I'll try this again.
Since an answer in inches will make more sense to people, I'll take the xs650 stroke and round it in inches, it's just under 3" so I'll use 3" to make it easy.I'll then test 2 different stroke to rod ratios, 1.6-1 (4.8") and 1.9-1 (5.7") as an extreme example. The difference between the 2 rod lenghts is .900" which is beyond what you could reasonably stuff in most engines just to show how little change in piston movement that even a radical modification will make. I'll also round answers to .XXXX" and .XXX deg.
I'm calculating this for 10 deg ATDC where most of the supposed effects are claimed to take place, and also for 90 deg ATDC to show the full effect.
Let's start with the 4.8" rod. You take half the stroke and multiply by the sine of 10 deg, answer: .2605. That's how far the crank has moved horiz. Divide that by the con rod length, answer: .005427. Hit invert, then tang on your calculator and you get an answer of 3.106 deg, this is the angle of the con rod when the crank is @ 10 deg. Take the cosine of that angle, .9985 and multiply by the con rod length, answer: 4.7929. This number is now the baseline for piston height since everything else will be the same for both motors.
Now for the 5.7" rod motor. Since the crank is the same, the .2605 is the same crank horiz movement. Divide this by the 5.7 con rod to get .0457. Hit invert then tang on your calculator to get a rod angle of 2.617 deg. Get the cosine of that angle, .99895 and multiply by the con rod to get 5.6941. Since the wrist pin has moved up .9" into the piston, we need to subtract that from 5.6941 to get 4.7941.
Now you subtract the 2 wrist pin heights from eachother 4.7929 from 4.7941 and you get... .0012"
Zippity doo dahh!!!!!
Obviously, this difference is too small to have any effect on ignition or combustion.
Now for 90 deg. Obviously, we don't need to do trig to find the horiz offset which is known at 1.5". Divide this by the con rod length (4.8), take that answer and hit invert tang on the calculator to get an angle of 17.354 deg. Take the cosine of this, .95448 and multiply by the con rod to get a wrist pin height of 4.5815. Now for the 5.7" rod. divide 1.5 by 5.7, then hit invert tang to get the angle of 14.744 deg. Get the cosine of that angle, .9670 times tha con rod length to get 5.2123. Subtract .9 to get 4.6123.
Subtract the two heights from eachother to get... .031". Given the fact that this is 90 deg, where not much is going on anyways,This difference is too small to effect anything to do with cam timing.
So do Long rods still have any defenders or do I need to continue this??