Gentlemen,
Dry crank singles (those already equipped with a reed valve crankcase) benefit from the additional check valve only with regard to oil containment.
Many OEM singles employ a pulse air system which draws from the inlet box. In opposition to deactivating said system (common practice) I often simply replace the air box tap with that of the crankcase spigot.
The majority of OEM multi cylinder street bike engines are also equipped with such a system. I once again take advantage by routing the crankcase vent to the scavenging inlet.
A vacuum in the crankcase reduces pumping losses and improves ring seal. (a result of increased pressure delta above and below the piston and ring assembly)
I would like to take credit, however, such is old school technology and has been around since the sixties.
I am indeed beginning to realize that unlike crankcase scavenging many of you have not been around since the sixties and therefore much of what I have to say comes across as brilliant. Some content is indeed brilliant, however, I cannot take credit for that which is not my own.
Kind Regards,
Dale
Reprint:
Concept: Apply a vacuum to the crankcase. Rather than putting a breather on the valve cover to let pressure out, actually suck the air out to create a vacuum.
Benefits of Crankcase Evacuation:
1) Cleans up installation (prevents oil leaks from crankcase sources)
2) Reduces parasitic losses from pistons pumping air
3) Improves ring seal
4) Increases HP by 4-7% depending on the application
5) Eliminates PCV and possibility of oil being sucked into intake system
Tech / Method:
Basically seal the crankcase and run a line from the crankcase to an air pump (or other source of vacuum) and from the air pump to a breather tank. Additionally, if necessary, use a vacuum relief valve to ensure vacuum does not get too great. If you put more than 12in vacuum on the crankcase, you can suck the oil off the front and rear main bearings. That would be a bad thing. Alternatively, with the crankcase sealed up tight to achieve good vacuum, you don't want your pump failing either which would allow a severe buildup of pressure in the crankcase then.
Typically, crankcase evacuation systems employ either a "race type" belt-driven pump or use exhaust as a source for vacuum. Both of those can have problems for street application. The belt-driven pumps are almost always specified for full race applications and therefore would need rebuilt every few thousand miles. If you use the exhaust as a source for vacuum and you have mufflers, you may end up with a buildup of oil in your exhaust ahead of the mufflers. Electric pumps can be used but our experience was they are problematic and don't produce enough vacuum.
