In a message dated 9/19/2010 9:19:17 A.M. Eastern Standard Time, msteitle@gmail.com writes:

Ed,

You and Lynn may have hit on something regarding the crankcase vent line being too small.  It may have been marginally acceptable with the side port engine, but way undersized for the fire-breathing p-port.  First time I ran it real hard, out came the seal.  I am using the stock vent line, but will go ahead and up-size it while I'm fixing the psru seal.  

Mark

The engine and PSRU are a pressurized system at about the same pressure. The engine is pressurized by blow by combustion gasses leaking past the side seals and oil scrapers. The PRSU is pressurized to the same value through the oil drain-back line. So, drain back would be impeded to some extent until the pressures are equal. After that it would be a constant until a power change is made that increases or decreases blow-by. Since the volume of the PSRU is so small it could be discounted as a drain-back problem, but the same pressure as the crank case will still be present. And that pressure added by the volume of lubricating oil (at 70 PSI or more) for the bearings, though not a large factor when the drain back hose diameter is adequate. 

 

Some builders use the factory side seal end play specification, allowing up to .004". I use zero end play in side seals. I install them tight, and then reduce length until the side seals and corner seal will just pop back up after being fully compressed into the rotor. The side seal is being pushed along by only one side of the corner seal. The seal end wears into the corner seal in short order. This starts making clearance right at break in. The direct outcome, is nearly zero blow by. Pressure not lost to blow by, is free HP.

 

This does not apply to Renesis engines where the side seal is exposed to exhaust gas flow and needs extra clearance to survive. (Because it runs hotter and gets longer).

 

Let us say that our engine has normal blow by of 12 cubic feet per minute. The stock breather pipe in the filler tube is smaller than 3/16". This means the gas velocity out of that pipe and into a catch can may be very high. So rich in energy that it can evacuate large amounts of oil droplets in the catch can. So, you make the vent pipe as large as is practical. That same 12 cubic feet, or more, still escapes, but now the crank case pressure is lower (less restriction) and gas velocity is way down. Down on energy and velocity the escaping gasses can no long lift oil droplets and drop them into the catch can. The catch can must have at least 5 times the open vent area of the hose cross section. You can look into the catch can and see how your engine is doing. Nothing in the can? Doing just fine. Some oil in the catch can? Watch engine closely.

 

A couple of inches in the catch can? Put in the spare engine.

 

The stock system of breathing into the intake manifold is fine for partial throttle, freeway speeds where only 25 HP is being used. For constant wide open throttle at about 6,000 RPM, and 160 HP, an adjustment must be made.

 

Why do old Mazdas smoke and use oil? They drink it through the breather hose connected to the intake manifold, as blow by increases with age. Nothing to do the OMP (Oil Metering Pump) at all.

 

The actual crank case pressure is a function of leak rate over vent tube cross section.

 

Lynn E. Hanover