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Old 22nd October 2019
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Continued from another thread regarding DK Customs testing..
Quote:
Originally Posted by bustert View Post
just using the numbers, it is a useful tool to determine top end wear.
for grins and giggles, take the sportster at .125cfm that being in good shape but later testing revels higher numbers, aka more blow-by and wear.
as per previous threads, the engine really does not have positive/negative swings, it goes by law of averages which the manometer shows. yes, down stroke does help oil circulation but the pressure diff'l is still constant.
in reality, the 1200cc engine has way more volume than that because you have to factor in the entire case enclosure.
the small amount of down stroke movement (the part that helps oil flow) is recovered on upstroke. the newer designs are more open than in the past which makes the law of averages more pronounced. the newer "u-tube" vs trap are less restrictive to oil flow also.
without consideration of orifice restrictions and just the numbers:
1cu/ft = 28,317cc
28,317cc / 1200cc (just using cyl displacement as example) = 23.6cc per stroke
if you factor in increase volume and restriction, the number will be lower.
of interest is the coast down number is the same which indicates that the slippage past the rings is consistent even though no combustion pressure. this slippage amount would be what is to be expelled. as rpm rises so does slippage and when it passes what the vent can handle, pressure rises, but one has to factor in time since there is less time for things to work.
so the point is, basically constant pressure and yes, vacuum is a pressure.
In your testing, around 5000 is where the pos and neg start getting close to equaling out from the timing hole.
And the negative pressure is still higher than pos.
But at that point in the tank, they are both damn near equaled.
I realize these are separate tests, but it seems to suggest that the positive pressure builds in the tank faster than in the cam chest at that engine speed.
(smaller container than the cam chest)
Could that just be a variant in testing?

From timing hole at 5000.


From oil tank at 5000.
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