Crankcase Evacuation System

Bill Kuran

Well Oiled
All-Star
Oct 14, 2009
1,403
Potomac, MD
First Name
Bill
Willys Model
  1. Wagon
Willys Year:
  1. 1960
Does anyone have experience with crankcase evacuation systems. I talking about a system that uses a vacuum pump to maintain crankcase pressure below atmospheric (vacuum). From what I have read, most systems are used with race applications; not street cars. Apparently it has to do with how much time the pump runs. Racing - very little. Street use - much more.

On my engine (L6-226), the down draft tube would be replaced with a -12 AN Male X Weld Bung. From there it would be plumbed to the vacuum pump then to an air/oil separator.
 
Bill, on a greatly different application, I just installed a Krank Vent on the breather of my 1935 Harley... It is a stroker with
a 5.25" stroke... Stock breather timing and breather ports... I added a Krank Vent to the vent pipe that normally vents to
atmosphere... I haven't dyno'd it but can feel a noticeable increase thruout the rpm range... The bike cruises smoother @
60-65 mph (2,400-2,600 rpm). The Krank Vent is a type of check valve on crankcase venting... It is supposed to
maintain negative pressure in the crankcase..


The reason for a timed breather in the original design: The displacement of the crankcase changes with piston position, so
the bottom end is constant sucking or blowing... The blowing absorbs more power than the sucking.. The timed
breather acts to neutralize the pressure variation..

With a greatly increased piston displacement, the breather system is overwhelmed and the crankcase average pressure
increases.. This absorbs power and increases operating temperature.. The added Krank Vent enhances the breather
system to help lower the crankcase average pressure.....


Your engine crankcase displacement should be pretty constant, because of crankshaft design... But, with a supercharger,
the crankcase pressures will be elevated.. Using a crankcase pump, should lower the temperature and make sealing
much easier..
 
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Bill, on a greatly different application, I just installed a Krank Vent on the breather of my 1935 Harley... It is a stroker with
a 5.25" stroke... Stock breather timing and breather ports... I added a Krank Vent to the vent pipe that normally vents to
atmosphere... I haven't dyno'd it but can feel a noticeable increase thruout the rpm range... The bike cruises smoother @
60-65 mph (2,400-2,600 rpm). The Krank Vent is a type of check valve on crankcase venting... It is supposed to
maintain negative pressure in the crankcase..

The reason for a timed breather in the original design: The displacement of the crankcase changes with piston position, so
the bottom end is constant sucking or blowing... The blowing absorbs more power than the sucking.. The timed
breather acts to neutralize the pressure variation..

With a greatly increased piston displacement, the breather system is overwhelmed and the crankcase average pressure
increases.. This absorbs power and increases operating temperature.. The added Krank Vent enhances the breather
system to help lower the crankcase average pressure.....

Your engine crankcase displacement should be pretty constant, because of crankshaft design... But, with a supercharger,
the crankcase pressures will be elevated.. Using a crankcase pump, should lower the temperature and make sealing
much easier..

Larry - Vacuum Pump Installation 1.jpgWith your application, the Krank Vent makes sense. As you said, the 226 engine's crankcase volume remains fairly constant. As far as I know, piston ring blow-by is the only contributing factor to increased crank case pressure. Blow-by will increase as engine rpm and power level increases. There are numerous articles available that explain the dynamics of how the piston rings seal as a function of rpm. If the rings seal better more force is delivered to the crank shaft.

Another advantage is that oil leaks are at the crank seals, etc., are minimized (maybe eliminated) if the crankcase is at a negative pressure. The photo here shows the system installed on what looks to be a very large displacement engine. These vacuum pumps are not designed to spin at a fairly low maximum rpm (around 4,000). The engine in the photo, the pulley sizes probably achieve about a two-to-one reduction.

Unfortunately, the only drive source available is a 7.25" crank mounted pulley. The pump would need a 10" diameter pulley.

I just repeating what I have learned about over the past week so...
 
Bill, you've made so many modifications on your engine, amazing really... I responded just so others would think about crankcase pressures..
Small changes like restricting the breather hose on an engine with a PCV can reduce oil leaks, and improve vacuum wiper operation...

I wonder if an electric powered pump would be do-able on automotive engines.

I am always interested in learning more about engines and how they operate... Your series of posts on making a 226 into a beautiful powerhouse is fantastic...
 
Bill, These GZ pumps (review linked) are for street applications. Does your oil pan have a windage tray to keep the mist down?

http://www.lsxmag.com/tech-stories/engine/tech-review-gzs-vacuum-pumps/

Tom - Thanks for link. I looked at those pumps, Moroso and Star Machine. No windage tray in the oil pan but this would be connect to the valve cover when the road draft tube is now connected so I am thinking (hoping) I won't run into a problem.

Bill, you've made so many modifications on your engine, amazing really... I responded just so others would think about crankcase pressures..
Small changes like restricting the breather hose on an engine with a PCV can reduce oil leaks, and improve vacuum wiper operation...

I wonder if an electric powered pump would be do-able on automotive engines.

I am always interested in learning more about engines and how they operate... Your series of posts on making a 226 into a beautiful powerhouse is fantastic...

Star Vacuum Pump with Mounting Bracket Assembly Rev (-) Right Rear View.jpgStar Vacuum Pump with Mounting Bracket Assembly Rev (-) Right Front View.jpgLarry - I used to believe that anything was doable but this is project is at the point where I question that idea. The easist, and most common, means to drive a vacuum pump is from the crankshaft pulley.

My engine only has one crankshaft pulley available and it is 7.25 inches diameter. In order to turn the pump at a reasonable speed, the driven pulley needs to be about 10" diameter.
The model renderings at the right show a Star Machine Mini vacuum pump mounting to the existing AC compressor bracket. The two unused holes in the bracket are the attachment point to the log-style intake manifold (not shown).

That arrange would work but the large pulley looks ridiculous. One comment I got was "nice Mercedes steering wheel you have there."




Electric Motor with Star Vacuum Pump Rev (-) - Isometric View.jpg




I did look at using a 12V DC electric motor to drive the pump. I like that idea because I could use PWM to control the pump speed based on feed back from a pressure (vacuum) sensor. This model rendering shows the concept.

The problem with an electric motor is the power limitation. I was told (but didn't listen) that the Star pump needs about 3KW (4HP) to achieve about 27" HG. I don't need anywhere near that vacuum so I decided to experiment with a 1/2HP motor. The one shown here is a Leeson Ironhorse motor.

So far, this is going nowhere but I do have a couple of more ideas to explore.



Backing off from the electric motor idea, I returned to the mechanical drive design and decided to try a speed reducer. Finding a small reduce that can handle the high input speed (close to 10,000 rpm) from the large diameter (7.25") driver pulley was a challenge.



Star Pump with Gear Head - Exploded View.jpgStar Pump with Gear Head - Isometric View.jpg
The model rendering here shows an Apex 3:1 planetary installed in front of the Star Mini pump.

I thought I had hit a home run with this design until I realized that I had installed the reducer backwards. Instead of slowing the pump down, I had increase its speed by a factor of three.

Turning the reduced around is possible but not an easy task because out end is not designed to support the load a driver pulley. To use it backwards, I needed to design a front bearing support for the pulley shaft.






Star Mini Vacuum Pump with Apex Dynamics AB115-060-003 Planetary Rev (A) Left Front Isometric Vi.pngStar Mini Vacuum Pump with Apex Dynamics AB115-060-003 Planetary Rev (A) Left Section View.png

The model rendering here shows the idea. The section view show a bearing in the front plate. If I were to use this, a second bearing would need to be installed to properly support the pulley shaft in a manner that doesn't transmit a load to planetary gears.

Unfortunately, I don't have the machining capability to make the adapters required to connect the pump to the motor or reducer. The geometry is too complex and would need to be sent to a machining center for fabrication. One-offs are expen$ive.

I am now back to the electric motor idea and doing some testing to determine the vacuum pump power requirements at the operating points I need for my engine (vacuum level and blow by volume).

Maybe I'll just reinstall the original draft tube...
 
Hi Bill. This idea is may not be worth a second thought. Could a small secondary turbo such as the one pictured below be placed downstream and plumed to scavenge the crankcase? Would it be possible to make it adjustable? http://www.ecotrons.com/products/small_engine_rhb31_vz21_turbocharger/

That is cool idea! I don't know for sure, but I'm willing to bet it could be made to work. It would require an exhaust source, oil supply and a way to turn the air flow into a vacuum source.

I'll keep the idea in my project file - thanks.
 
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