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  #21  
Old 19th October 2019
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These are some good bookmarks on breather mods and CC pressure in the XLForum's Sportsterpedia:

Breather / Venting Mods
http://www.sportsterpedia.com/doku.p...:ref:engmech05

Evo Crankcase Pressure and Engine Breathing:
http://www.sportsterpedia.com/doku.p...:ref:engmech04
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Reference the XLFORUM'S Sportsterpedia for additional technical information & advice

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  #22  
Old 20th October 2019
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some interesting theory but in actuality it is slightly diff.
interesting numbers on vent cfm, which suggest something else is going on which supports the manometer numbers.
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  #23  
Old 20th October 2019
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Quote:
Originally Posted by bustert View Post
some interesting theory but in actuality it is slightly diff.
interesting numbers on vent cfm, which suggest something else is going on which supports the manometer numbers.
Did you test CFMs?
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  #24  
Old 21st October 2019
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dk customs numbers in your sportsterpedia link.
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  #25  
Old 21st October 2019
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Oh.
Yeah there is gonna be some variance.
I've seen the balloon test and Aaron's breather dyno results but I guess your slack tube testing hit home the best for me.
But they all support each other basically.

edit:
I knew there was a point at which positive pressure would be greater.
And I assumed that would be around 5000 RPM.

But based on what I've read, I assumed pressure would be more to the 'slight' vacuum' side until that point.
Your testing shows it to be a gradual change in pressure as the RPM rises.
This shows just how pressure can change with the addition of air leaks and failed breather valves... and my removing the oil cap.

Last edited by Hippysmack; 22nd October 2019 at 04:56..
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  #26  
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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.
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  #27  
Old 22nd October 2019
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Quote:
Originally Posted by bustert View Post
slippage past the rings is consistent even though no combustion pressure. 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.
Just like a compression test, you'll always have a certain amount of leakage into the bottom thru the rings.
And yes it is interesting that it is so consistent.

I don't feel like the DK test was awful scientific but just another tool.
I am not quite understanding the 'no combustion' though.
They wrote chopping the throttle to 0% with the clutch pulled.
But that was to let the engine decel on it's own while still running is what I gathered "on throttle let-off" even though they used the word chop.
So there was combustion at the time it seems.

The time doesn't show up in your tests?
I would think increased positive while the negative is lowered would also include stroke timing with increased RPM.
All one big stew.

trucker2800,
Any luck finding a breather valve?

buster, if you wouldn't mind, I'd like to continue this conversation in the CC pressure thread.
http://xlforum.net/forums/showthread.php?t=2073932

Last edited by Hippysmack; 22nd October 2019 at 05:54..
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  #28  
Old 22nd October 2019
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according to your sportsterpedia, the numbers are consistent across the board from idle to cruise to hard accel to coast down.
rings float so it takes pressure to force them to seal.
even combustion pressure is subject to law of averages even though most only look at peak numbers.
when testing diesel engines, you are looking at law of averages which is way lower than peak pressure. now if you would use a more modern electronic recorder, you could plot the entire range but the old mechanical gauge set which is snub to reduce oscillation shows average numbers and you judge by this and mfg's data.
on the coast down, they did make it more consistent with idle speed, no load via clutch pulled in. but idle pressure is way diff than loaded engine. this test makes no since because the idle test is the same, maybe the numbers would be diff if the engine was in a true coast down.

Last edited by bustert; 22nd October 2019 at 15:45..
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  #29  
Old 22nd October 2019
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hummmm????
i wonder about the terminology???
clutch in as in engaged
clutch out as in disengaged
perhaps you could get some clarification as this would shed some light on the above, does not make sense as surely they would know the test would be the same.
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  #30  
Old 22nd October 2019
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Recreate this in your head:


In this test, air was captured and measured as to how much water volume was displaced in a fixed period of time.
Taking the liquid ounce displacement, you can convert that to Cubic Feet Per Minute (CFM) There are 957.50649350649 U.S. fluid oz. in 1 Cubic Foot.
Results:
Sportsters move the least amount of air through the breathers. Twin Cams move the most amount of air through the breathers, with little difference between air cooled and Twin Cooled.
Milwaukee-Eights move more air than Sportsters, but little more than half as much as the Twin Cams through the breathers.
Even more surprising is the least amount of air is moved on all bikes while at cruising RPM.
The only way to get a significant amount of air to move through the Sportsters was to get the RPM up around redline.
(and that crankcase pressure was probably because the valves were beginning to float) The most amount of air is moved through the breathers at idle, during hard acceleration and during deceleration.


The criteria for both DKs and Aaron's testing wasn't to answer some of the questions we've had.
DK's criteria was 'how much air was passed out the breather vents at idle, under a load, at cruising speeds and on throttle let-off' for different model engines.
So there main concern was how much air moved out of the engine.
Your testing backs up their data showing at most of the RPM range, there is more vacuum than positive pressure.
And it's the positive that leaves the engine. Therefore, their results are equaled out more.
Even though there is normal blowby throughout the RPM range, the vacuum created buffers that.
We've read and heard the phrase 'slight vacuum' from many sources.
But your slack tubes put a visual to the process showing that the 'slight vacuum' is not really a stagnant number but a moving range.

15 inches of vacuum that all of a sudden is hit by 5 inches of positive pressure rolling the throttle still yields 10 inches of vacuum at the time.
So there would be no air moving into the balloon or container at that point.

Aaron's testing was with the normal breather vents (with and without the timing hole plug removed) in the interest of measuring whether either would increase HP.

edit:
In theory and during that transition from 15" to 10" vacuum, more oil is pushed toward the scavenge hole in the sump, the pump gets a fatter supply of oil to send to the tank, pressure goes up in the air space in the tank due to the restriction size of the vent.

Aaron said "necking the timing hole down to a 3/8“ hole and connecting 2 feet of hose adds a pretty significant restriction.
The vent hose from the tank to the cam chest is also a restriction as more air/oil is forced into the tank but the vent restriction remains the same.

That's why I was wondering about your testing from the oil tank showing the pressure equaling faster than in the crankcase.
That would suggest the tank is being overloaded before oil pukes out the A/C.

[QUOTE=bustert;5783633]hummmm????
i wonder about the terminology???
clutch in as in engaged
clutch out as in disengaged
QUOTE]

Technically, yes.
But normally 'clutch in' would be referring to the clutch lever as in 'pulled in' I believe.

Last edited by Hippysmack; 22nd October 2019 at 19:53..
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