I have been running an open crankcase breather with a catch can.  It works good in terms of performance, but probably isn’t doing our atmosphere any favors.  I can do better.  It was time to see if I could recirculate the crankcase vapors into my induction system without sacrificing any performance or economy.

I also wanted to revisit the Hayden KrankVent to see if I could improve performance.  Maybe I could get a little better fuel economy, or crisper throttle response.  The KrankVent is a one-way check valve that is installed in the breather hose.  It lets air pass out of the crankcase when the piston moves down, but prevents air from being returned to the crankcase when the piston moves up.  With the check valve installed in the breather system, a vacuum should develop in the crankcase.  The vacuum will increase the differential pressure across the piston rings, and should result in improved power and efficiency.  Seems like a good idea to me.

Back in March of 2020 I tested the KrankVent .  Other than adding weight, the KrankVent didn’t seem to do much.  I felt that the concept was technically sound, so I wanted to give it another try.  When I did the initial installation and tests, I was using a compound gage graduated in inches of mercury on the vacuum scale, and pounds per square inch on the pressure scale.  I always felt that the instrument I used was not sensitive enough to provide a clear picture of how the engine was behaving.  The pressure I was trying to measure was extremely low (about 1 to 1.5 inches Hg).  I really needed to be using a water manometer.  One inch of mercury is equivalent to 13.6 inches of water.  The resolution on a water manometer would be a vast improvement.

This is a link to the old KrankVent post.  It provides some background info if you are interested.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1585377641

This old post provides details on how my original catch can was constructed.  Construction of the new earth-friendly catch can is almost identical.  

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1570415428

You might ask why not run the breather hose directly into the air boot.  You want the catch can with the separator system to prevent any oil droplets or aerosols from entering the induction system.  Oil in the combustion air promotes detonation.  That might not be a problem on a low-compression engine, but on a high compression engine it could cause trouble.  Best to keep oil out of the combustion chamber.

One thing that would most certainly make this breather system a huge mess would be big-league vacuum in the induction tract (the section of the air intake system between the air filter and the carburetor).  I didn’t think that a little vacuum in the induction tract would be a concern, but a high vacuum in this area would tend to suck oil out of the engine.  I do not want oil in my combustion air.   If a significant vacuum is developed in my induction tract, the earth-friendly breather system is probably a non-starter.  

The oil-in-the-air problem is evident on the stock airbox.  With the stock paper filter and the super-restrictive airbox, it’s not uncommon to find oil accumulation.  That’s why it has the drain tube & plug.  You have to periodically dump the sludge out.

The long rubber hose on the bottom of the airbox is for draining oil.  The drain hose connects downstream of the air filter.  It is located in between the air filter and the carburetor inlet.  The other drain you see, the one with the clear plastic cap, is a drain used to dump water and debris that accumulate upstream of the filter element.  

It was time to see just how much vacuum I could expect in my induction system.  I hooked up a water manometer to the air boot fitting and ran the engine.  Zero vacuum.  That K&N filter is excellent.  BTW, not only does it flow a lot of air, but there is also never any dirt in my induction system.  It does a good job of filtering.

Now that I knew that the induction vacuum wouldn’t cause a problem, it was time to see what sort of pressure or vacuum I could expect in the crankcase.  I was into my long-term test of the 94mm flat-top piston, and the engine was running pretty good.  I think it was a decent representation of a normal LS650 engine in good mechanical condition.  The crankcase was vented to atmosphere via my standard breather system.

The manometer got attached to the crankcase fill plug.   The crankcase actually developed a slight pressure, about 1.5” H2O.  Before, when I tested crankcase pressure using a compound gage, it pulled vacuum.  But that was with the engine under a significant load.  I can’t ride around with a water manometer strapped to the handlebars, so I just gotta take what I can get.  But it sure seems like it doesn’t develop a vacuum with a breather vented to atmosphere.

This YouTube video shows the test.  It’s interesting.

https://www.youtube.com/watch?v=rfYuOtY6DIM

With the KrankVent installed, it pulled about 16” H2O vacuum.  Progress.

This YouTube video shows the KrankVent in action.  The water manometer leaves no doubt, the KrankVent sucks.

https://www.youtube.com/watch?v=4hOOgvQkTc4

BTW, you will notice that it holds the vacuum after the engine is secured.  I timed the vacuum drop.  It still had 10” H2O vacuum after a 10-minute drop test.  It’s a tight motor.  Pretty cool.

I rode it around like this for several hundred miles.  Same results as the test I did in 2020.  It didn’t feel any faster.  Throttle response was the same.  Fuel economy was the same.  The only thing I noticed was the oil pressure was just a bit lower.  To make sure it wasn’t my imagination, I did a test to verify that the oil pressure went down a bit when the vacuum in the crankcase went up.

This YouTube video shows the oil pressure variation and its relationship to the crankcase vacuum.  It’s a really small drop in pressure.

https://www.youtube.com/watch?v=s0iC4YrHvyA