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  #41  
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Patrick I'm still taking in that PDF.
For posterity, I've never seen it before, but I can relate.
Even though the article is about auto engines, he has mention to dry sump engines but the piece is geared toward wet sump.
But the breathing portion is relative.

He says:
In common road engines, it is usually required to have a crankcase pressure slightly lower than the atmospheric one because this will impede any oil leakages: common target value for the crankcase pressure is around 20 to 30 hPa lower than the atmospheric pressure.

However,
The actual amount of vacuum is dictated by each manuf. and I believe that has to do with seal limitations.
Since wet sumps have the oil pump submerged as a sump pump, scavenging isn't as big an issue as dry sumps in concern of higher vacuum.
Gravity does overcome vacuum in that instance.
Not arguing the weights of gravity against vacuum.
But our engines have a disconnect between the pump and scavenge oil.
That is where the conundrum exists and the affects of vacuum and windage affect what the pump is able to find in order to remove.

I made a conversion chart for pressure measurements.
20 to 30 hPa is roughly 8-12 in of water column.
http://www.sportsterpedia.com/doku.p...k:ref:genmsr04
So there is a difference in vacuum allowances for Sportsters as opposed to autos.
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  #42  
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Quote:
Originally Posted by thefrenchowl View Post
If we were not already confused, This will make sure we indeed are!!!...

https://core.ac.uk/download/pdf/72787231.pdf
...
Hhmmm, looks like it is a download from the UK, but the thesis was done at the University of Windsor in Ontario, Canada
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  #43  
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Elevation may have something to do with the vacuum per region.
Not entirely versed on that aspect.
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This is what I wanted to see.
Matching this to the 57-71 and see the changes.



If the drawings are right now (please check).
Here is what I've been seeing but not being able to convey.
71 900< wet sumps easier than 72 1000> ?

The big change (in CC pressure points) between my two drawings is the starting point and amount of closed vacuum on upstroke due to the gear widths.
The positive pressure points are the same between the two different bores.


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  #45  
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No, Hippy, correction, red line indicates tower slot closed hence vaccum creation:



If tower slot is open, whichever you want to look at it, crankcase is open to A.P. So, 72 > 76 from BDC to 90 deg ABDC, crankcase can admit air from A.P. via timing cavity = no vaccum.

This was the timing adopted on the KR quite early by the race dept after testing.

I believe this was to cancel some of the vaccum which was probably a tad too high when tower slot closes at BDC.

I do say "can admit", not "admits" cause, with inertia and rotating speed, I'm not sure at all oil mist escaping on the downstroke will have time to fully reverse its direction from BDC to 90 Deg ABDC.

So this 72 > 76 breather timing could be similar thinking (which certainly works) to RFE and RFA on the cams, take advantage of gas inertia to better scavenge oil mist from crankcase.

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Closing at BDC eats HP through pumping loss. They figured out pretty quickly that it could be left open longer with no negative effect thus reducing that loss.
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Patrick, you're right. But I was just thinking in terms of where the vacuum stopped building.
45 deg to TDC is where one piston is going up and the other going down so I didn't count that as more vacuum.
But like you said earlier, the higher up in the cyls that is anyway.

mrmom, that of course, sounds right. Less drag on upstroke.

But now I come to 77-up which closes at BDC with the one way valve.

Would that be deemed as an acceptable pumping loss due to EPA regs?
But the vent still went to atmosphere until 79.
I found some information on the changes made starting Dec, 1977.
The MoCo made some changes by then but were reluctant in going all out.

Harley Davidson and the United States Clean Air Act of 1978:
http://www.sportsterpedia.com/doku.p...story:99xx-01f

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BT's kept the timed breather years after the Sportster stopped using it.
I don't know why as I haven't looked into them very much.

Here is what I see as 1977-present Sportster engine breathing.
There are a lot of differences;
1 or 2 breather valves, valve size and construction, venting from the cam cover or heads and added influences everywhere...

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Quote:
Originally Posted by Hippysmack View Post
But now I come to 77-up which closes at BDC with the one way valve.
Would that be deemed as an acceptable pumping loss due to EPA regs?
[/url]
OK, I'm depressed nobody answered this.

I made some more drawings.
The figures are not accurate since I've found nobody that CC'd their crankcase and gearcase.
But the thought is the same.

This one is just an extension of the degree wheel drawing regarding vacuum.


This one shows that even though they went back to closing the breather at BDC, crankcase pressure didn't suffer for it.
The holes opened up in the cam wall increased the volume of crankcase air.
The pistons are the same, travel is the same.
But in 77> engines, vacuum is lowering a bigger amount of air.
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tec evolves and it makes sense to let the engine do its thing by natural flow function than trying to time things. if you take the timing window out of the picture, will operate like the evo, as long as flow out the vent valve can be maintained. the big issue here is the way oil is removed from the flywheel compartment, big restriction but needed due to design.
the japanese are ahead of the curve, americans are toooo slow. ex: americans used egr valves and controllers, japan made it a function of the engine. crank vent and vacuum part of the engine function and no need for pcv cross ventilation which closed off under high loads so had to backup through the atmospheric side to air cleaner.
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