The Sportster and Buell Motorcycle Forum - The XLFORUM® - Sportster Crankcase Pressure / Engine Breathing / Wetsumping and Mods

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- - Sportster Crankcase Pressure / Engine Breathing / Wetsumping and Mods (http://xlforum.net/forums/showthread.php?t=2073932)

Quote:

Originally Posted by bustert (Post 5761678)

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.

Again, don't know if I'm learning something or getting dumber.
But I can take a shot at the filter thing at best.
The volume pulled into the chambers is controlled by the cylinders.
What is seen inside the filter area is outside to inside differential (aka vacuum) via the cylinder fill like you mentioned.

The restriction of the media makes that higher or lower differential until the cylinder is full.
Then it equals out.
The size of the filter is the same as the size of the breather bolt hole.
A smaller filter makes for a smaller volume of air to manipulate (increasing the air speed thru the filter)
While the larger one allows for a larger volume of air to be displaced at the same cylinder fill rate (lowering the air speed thru the filter)

It's up to the media as to what speed it will allow thru it at what restriction rate.
The restriction goes up as oil saturates the media.

A K&N type media lessens the restriction due to the larger hole surfaces thru it (lowering air speed).

Undoubtedly, it's the less restriction (lower air speed) that the engine likes the best. ?
Easier less restricted fill?

My SBC runs and feels better with faster carb response with the larger A/C.
Maybe that's the media restriction of the smaller A/C that it doesn't like.
My vacuum secondaries always liked the bigger A/C.

i think we are on diff tangents.
taking a break from the heat/humidity, building a new shop or second shop, why i ask, geeeez at 68 i think i know when to quit.
looks like i have chicken pox, hate those 6010 rods doing over head up hill.
the forum has reduced past post on our page so i can't clip/paste.
your are def on track with something you said eariler, was hope for you to expand it because i think you are absolutely right.
post #32

Quote:

Originally Posted by bustert (Post 5761736)

the forum has reduced past post on our page so i can't clip/paste.

It's done what?

Quote:

Originally Posted by Hippysmack (Post 5761684)

My SBC runs and feels better with faster carb response with the larger A/C.
Maybe that's the media restriction of the smaller A/C that it doesn't like.
My vacuum secondaries always liked the bigger A/C.

It has to do with restriction. Restriction is usually measured by pressure drop. Difference in pressure between atmospheric and inside your air cleaner assy. It will vary depending on how much air your engine is inhaling. Used to be measured in inches of hg or inches of water.

Many of the old quadrajet equipped cars came from the factory with single snorkle air cleaner housings. There was enough restriction they wouldn't open the secondary air doors. Flipping the air cleaner lid made a huge difference as it allowed the secondaries to open.

That makes sense.
Heh, my lid's flipped as we speak.
The assembly is taller than the stud...
I did open it up last weekend and the secondary's did well...
I'm running an Edlebrock at the moment. This motor's too small for the 750 Holley.
Last motor liked it but the float was set at the lowest point plus about 1/2 of a thread.
I know, street motor, but it's all that vice I have left. :D

I haven't thought a lot of the affects on the Sportster carb from A/Cs.
Obviously, there are gains from running the vent lines elsewhere.
As well as cons I suppose.

Quote:

Originally Posted by Hippysmack (Post 5761754)

Obviously, there are gains from running the vent lines elsewhere.
As well as cons I suppose.

The advantage is not putting what's coming out of the breather into the intake. You want your carb or throttle body inhaling cool clean air not oil mist and combustion by-products from the crankcase.

Not routing the breather into the intake also keeps the throttle blade and the throat area right where it closes cleaner. They will get a crud build up that needs cleaned periodically or they develop off idle issues.

Quote:

Originally Posted by Hippysmack (Post 5761528)

The holes in the 04 Up bolts are stepped.
They are smaller on the head side as above but bigger on the A/C side.
That creates more of a restriction than 91-03 models.
The restriction can do a couple things.
It will create more backpressure inside the engine until a stronger force is applied from inside.
That stronger force would be the air created on downstroke.
(edit: In a perfect world), The downstroke won't be impeded so the force won't slow down.
So the major result would be air moving out at a faster rate thru the smaller hole.

'Why' I'm still working on but that was by design.
I feel it was to move CC pressure out of the engine faster as that wouldn't really do a lot for keeping pressure in on an OEM engine.
They also added the piston squirters in the CC which adds more oil to the sump / creates more responsibility on the oil pump scavenge to remove that drain oil faster and keep it off the wheels.
(which they didn't upgrade the scavenge section until 07)

The results of using the bigger holed bolt using the above reasoning would be a slower rate of outflow.
But the timing of the upstroke is the same which then pulls a vacuum.
The umbrella will close down only when inside air pressure is lower than outside air pressure.
If the inside pressure can't get out fast enough before piston upstroke happens the umbrella may 'float' or not close all the way.
If the umbrella floats, X amount extra air is pulled in until it does close.
(on top of what didn't get completely out on the last downstroke = more air in the engine on the next downstoke = oil puking out the breather)

How much slower the bigger bolt hole yields, I don't know.
If it's a problem, I don't know.
I don't have any flow data which would be what is needed.
That's why I was reading bunny32's comments closely.

Since you've upgraded to bigger pistons, there will be more positive pressure displaced out the breathers on downstroke.
It's not clear to me just how much of a change the smaller hole made.
But again, it was by design to OEM specs internally.

I'd suspect it could contribute to an 'out of balance' between positive and negative pressures inside.
(edit: to rephrase, I suspect it was meant to manipulate that balance)
But it'd be more of a concern if you had higher CC pressure / vacuum than was healthy.
(which would probably show itself if it was a big problem to the engine)

bustert, I'm not sure where you're going, or rather what angle.
Frankly, I'm not sure where I've been either. :coffee

The piston squirters added more oil in the sump ...
No they didn't, sort of.
The only thing the squirters did was add the same volume of oil in the sump at a faster rate.
Feed / scavenge gerotors are the same size before and after they started using them.
http://sportsterpedia.com/lib/exe/fe...hippysmack.jpg
http://sportsterpedia.com/lib/exe/fe...hippysmack.jpg

Yin-Yang:
Faster oil rate in the sump without added air means it needs to move air out faster to keep more amounts of oil from coming into suspension?
More oil in the sump at once gives to more suspended oil (or thicker air/oil mist) on upstroke.
Thus the smaller holes in the bolts for faster air removal before suspension.
:geek

Quote:

Originally Posted by Tomcatt (Post 5761769)

That'll be my next step on my Sporty.
I finally got all I wanted done to the engine and got her running good.
So I got a decent base to start with on an A/C mod.
Just makes it easier when figuring changes.

I haven't run a SBC vent into the carb since I was old enough to buy my first shiny chrome assembly. :)
2 things creep out of memory are cleaning out gunk from quadrojets and scraping Quaker State glue out of the valve covers.
But the Sportster engine is a good size learning curve from my shade tree education.
So I guess I've been taking baby steps.

mr. folkie i used to be able to go way back on the posts but now only 4 pages are shown. i am sure everything is still there, just have to search in a diff way.
storm coming, check everything out, for sure my generator.
i'll have to get back to the thread, but a passing thought there mr. hippy: rethink the breather orifice effect. it sorta goes hand in hand with another observation you made.
since i can't clip & paste, will use a method that mr. folkie uses and type everything in a word processor and then clip & paste so you do not time out on the forum.

Quote:

Originally Posted by bustert (Post 5761920)

mr. folkie i used to be able to go way back on the posts but now only 4 pages are shown.

Oh, do you mean on the 'New Posts' page? Everything is still there. You can look in individual Forum sections. In this section, that this thread is in (Engine Bottom End), for example, there are 81 pages of threads, which is everything that has ever been posted in the section.