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-   -   Sportster Crankcase Pressure / Engine Breathing / Wetsumping and Mods (

Hippysmack 10th July 2019 02:25


Originally Posted by 60Gunner (Post 5761589)
Ya know, routed like the factory does, it's in a low pressure area and wouldn't raise crankcase pressure as much as routed to atmospheric pressure such as is the case of most including myself. Maybe it's a good thing it's bigger? Smaller in this case may just build too much pressure and blow seals and gaskets?

The factory bolts are installed long enough to be in the low pressure (vacuum) area of the A/C as you mentioned.
There is less vacuum inside a smaller A/C (from my experiences with my truck anyway)
A big hunka chunka A/C on top of my carb pulls more (inside the unit) vacuum than a small one.
Sounds meaner too. :smoke
edit: (That's probably better stated as more volume)

So, you do lose that low pressure on the outlet of the vent using the big ham can.
But plugging it into a smaller A/C I'd think would have less affect.
There is a cause and affect between the manifold and the A/C I'd think.

But the only reason it should raise pressure significantly is if the umbrella fails in one form or another.
On the other hand, it also is important how fast the umbrella closes.
With the A/C in line, upon a floating umbrella condition, you'd have less air enter the engine than with it left to atmosphere.
So there is that.

60Gunner 10th July 2019 02:36

Well im not in the AC. I tee under it then cross over to the other side. Then back and drop down under the bike. I never considered the size of the holes in the tee tho. A little smaller that the bolts but not as small as the factory ones.

Hippysmack 10th July 2019 02:49

I don't know.
With the bigger pistons, I'm not sure what that means other than higher positive and negatives pressure while running.
2 things.
As long as it's not puking out the vents, your yin-yang should be working for you in some respect.
As long your scavenger pump isn't getting behind the ball, you shouldn't be suspending too much oil to puke out the vents.

Basically, if it ain't broke, don't fix it. :)

Hippysmack 10th July 2019 03:05

Vacuum based solenoid?


Well, vacuum is on/off on our Sporties.

60Gunner 10th July 2019 03:18

I don't puke a drop of oil. Funny cuz I would occasionally when everything was stock.

Hippysmack 10th July 2019 03:22


Originally Posted by 60Gunner (Post 5761615)
I don't puke a drop of oil. Funny cuz I would occasionally when everything was stock.

That's interesting.
Wonder why that is?
Sounds like the balance in your engine was improved somehow.
But what?

Jollly Rogers 10th July 2019 13:41


Originally Posted by Hippysmack (Post 5761617)
That's interesting.
Wonder why that is?
Sounds like the balance in your engine was improved somehow.
But what?

I’d bet he’s got a better ring seal and proper break in that has eliminated the OE blow by.

Hippysmack 10th July 2019 13:48

Yeah, I agree with that.
That's why I was thinking time will tell.
Blow-by is always present.
Newish rings will seal better now than later on.
It's the later on that may reveal more.
Like I said, it may not be an issue. He is not OEM anymore.
So that may have changed things somewhat.
I need to come up with some test equipment in order to have a better opinion on the subject.

bustert 10th July 2019 14:25

i do not think the position of the breather bolts are of any special engineering, they had to fall with the design.
as far as surface area of the filter and its shape, there is a correlation. but of more importance is the restriction the media imposes. where is the low pressure actually located?? it is not inside the filter area although the pressure diff'l between inside/outside is there. the diff'l between source and surrounding area is similar to a decibel, exponentially lessen with distance.
an engine can ONLY use a finite amount of air so putting a larger filter than required does little, the only exception being if the restriction is reduced caused by the media.
awhile back, in a thread, it was mentioned why oil in the filter comes about, but this in correlation to the older design which i believe why hd went to smaller holes.
many things to do, and bad weather coming, will have to jump back.
no tom terriffic ideas yet??? any industrial mechanics out there??? hint, look at the waukesha 7042 vent system/exhausts.

60Gunner 10th July 2019 15:17

I should add the breather system was stock as well.

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