Crankcase Scavenging

[Nerobro]

here I am almost wishing I had a twin now. A twin would give me an easy way to ensure low crankcase pressures. (put on a check valve, and when teh pistons go down, forcing air out of the crankcase, and then when they go up, the check valve will keep the air from re-entering... viola, low crankcase pressures)

As aformentioned, low crankcase pressures reduce foaming, control oil better, make the rings seal better, reduce pumping losses, increse horsepower by making the pistons see a greater pressure ratio... yes it's a good thing.

Now... just VENTILATING the crankcase.. doesn't provide much. If your rings aren't trash, it really isn't necessary to improve crankcase ventilation.

Small electric pumps are avilable for pulling a vaccum in the crankcase. You don't need much of one for a 700cc 4cyl.

Now the reason I didn't reply when this was first posted... was that he was suggesting the use of the exhaust to generate these low crankcase pressures. I've seen this done on high preformance car engines. But.... I don't see them generating MUCH of a vaccum. Pro-stock, Nascar, F1, and many other racing classes use dry sump systems, which artificially create a low pressure crankcase. Using the exhaust trick isn't nearly as effective, but... I"m sure provides "some" benifit.

If you were me. You'd use a small electric pump to do it. Or find some way of driving it off the crankshaft.

 

[Billy Ricks]

These pumps might be just what the doctor ordered. http://www.virtualpumps.com. They have the benefit of being very small and one line has a 5,000 hour life expectancy.

 

[gsbill]

Those are cool pumps...the link doesnt work...Loose the index.htm at the end

 

[Nerobro]

OOOOOOH.... Those pumps give me ideas.... I wonder what good it would do for my focus. Hmm.. maybe just hook it up to my GS

 

[Billy Ricks]

The nice thing about the Virtual pumps is the size of fitting that it would take to hook up. 1/16" vacuum line is all it needs so drilling and tapping the filler cap is all it would take. Any idea of how much barometric pressure be best? If you look at the specs they list what they can pull.

 

[gsbill]

I have no idea on that...You would need to research further..

 

[Anonymous]

The nice thing about the Virtual pumps is the size of fitting that it would take to hook up. 1/16" vacuum line is all it needs so drilling and tapping the filler cap is all it would take. Any idea of how much barometric pressure be best?

You may want a larger hose size to flow enough air to maintain the vacuum level. Remember, your engine is not a sealed system, it leaks and the pump must be able to keep up with the leakage.

I recall seeing an article about the Star Racing Pro Stock bike Angele Seeling won her first title on and they said it ran something like 20-25" Hg, which is a lot. I would think you would notice benefits even at 10" or so. More is better, but I am not sure how much better for a street bike.

Mark

 

[Nerobro]

I was about to say 20"hg. I with I had a PSI number for that. My mind works in PSI not inches of mercury ;-)

A good engine is fairly well sealed. I think the biggest worry will be sucking gaskets out of place.

 

[Anonymous]

I was about to say 20"hg. I with I had a PSI number for that.

Well, 29.92" = 14.7psi (standard atmosphere), so you can use that to calculate the psi at 20".

psi = (20/29.92) x 14.7 = 9.83 psi


Mark

 

[Keith Winter]

Wow and I always thought vacuum pumps were for men with problems and pregnant women!!
My question is, does all this crankcase vacuum have any affect on the amount of oil that comes up the piston in the oil rings? Maybe I'm out to lunch on this one, but you do need that oil comeing up with the piston and if you had a negative pressure in there would that not reduce the amount of oil causing the rings to wear faster? On raceing machines they change the rings alot more than street riders would, so for them ring wear isn't a issue, maybe. Also I always thought the crankcase venting provided some cooling affect as well. Here again for raceing with run times of 8 to 11 seconds it makes no difference, but for 8 to 11 HOURS of street riding I would think cooling is a issue. Is this all just more vacuum, only in my head, or can you race guys explain it to me.
Thanks

 

[Nerobro]

If anything the negative pressure improves oiling. It causes oil mist to not stay a mist, and drop down to where the oil pump can move it. Same for foaming issues. Crankcase ventilation is mostly to compensate for temprature changes, not for cooling. In fact, there is usually only one vent, so there is no "real" flow.

Endurance roadracers almost exclusively use dry sump (and the necesary low crank case pressures) to ensure good oiling and make sure the engine lasts the race. Wet sumps in cars cause "interesing" issues when you take turns at 1G+

Hmm.. 9psi. so that could be nearly 10% more force on the piston... *grins*

 

[KEITH KRAUSE]

I don't know anything about the vacuum pumps but if anyone's interested in my version of a catch can then check out my website.
I used the plastic dust cover from my Progressive shocks as a catch. I sealed the bottom with a plastic cutout. It straps to the frame with a cable tie.
The K&N crankcase filter fits perfectly. The filters hose rests in a notch I cut. The notch keeps the filter about a 1/2" above the bottom. Sometimes after a full day of riding, usually faster riding, I get some accumulation. About once every two weeks I just lift the hose up and dab a paper napkin in there. Very clean, out of sight being under the seat.
If you want to see it, click the WWW symbol below. It's near the end of my pic's.

 

[gsbill]

K, Thats a nice clean job..Looks great...Style and function!

 

[Anonymous]

Negative crankcase pressure

Negative crankcase pressure

You can and should run some negaitve crankcase pressure. Old drag race cars would run a hose from a PCV Valve in the valve cover to each exhaust header just after the collector. Don't run it to the carbs. It will run lean and creat jetting problems. Or, Many GS cars use an electric vacuum pump just for this reason. They make more power and the rings are better able to control the oil. Since many new cars use narrow rings like the bikes do now.

GREG

 

[lecroy]

I ran three tanks of fuel in my stock GS1100ESD and captured the vent into my normal style catch can. This is the waste....

I can believe that Hap is seeing a nice film on his bike and I also believe there is nothing wrong with his bike and that this amount is going to be normal. I rebuilt this engine not too long ago and it's running good.