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Oil Separator for High Speed Driving
By Steve Grosekemper
During any high speed or long sustained speed event we all know that additional oil consumption is expected. The reason for that is not because the engine is consuming more oil past the rings or valve
guides. The reason is that the oil is being churned up, causing a higher than normal vapor in the oil. This oil vapor is then drawn into the intake system of the engine and burned through normal
combustion. On certain model cars Porsche installs a device known as an oil separator. The purpose of this device is to separate the oil from the vapor. The oil is then returned to the crankcase and
the pure vapor is sent to the intake system, decreasing the amount of oil that is lost in the combustion process. The models using these devices are usually very high revving, high horsepower per
liter cars (Turbo charged cars) or large displacement per cylinder engines (944/968).
The 944, 951, and 968 use a separator that is specifically designed for their application and does not transfer well to other applications. The remaining two turbo charged cars (911 Turbo and 924
Turbo) have devices which do adapt well to other models. There are also after market versions that work well, but not as well as their more expensive factory counterparts. This is due to the fact
that they have only one chamber, instead of the two that the factory units use.
The first (Figure 1) is a JAZ after-market unit installed in a large displacement 911 racing engine. It has been
modified to let the oil automatically return back to the engine case. The valve located on the bottom of the container is normally closed and is supposed to be drained periodically. It is now left in
the open position, and a 12 mm banjo fitting has been bored out to accept a standard 14 mm threaded banjo bolt. This banjo bolt is installed where a temperature sensor would normally go. A 7mm
breather hose is installed between the two.
The second (Figure 2) is a 911 turbo unit (part #930.107.321.01), installed on a high performance 914/6 with PMO
water shield air cleaners. This unit works well on most all 911 applications with a vented air cleaner, because the breather hose fittings are of the correct diameter. This eliminates the need for
hose adapters or reducers. The bottom return hose is a 944 coolant hose (part #944.106.241.03). It is normally used to join the water pump to the heater pipe on the right side of the cam housing. For
our application, we attach the large end to the oil separator and the small end to a fitting on the engine breather cover (as in Figure 1). A breather cover that has a 14mm threaded boss must be
used. The fitting we use comes from the left side of a 911SC air box, where the brake booster hooks up. (part #911.125341.01).
The third (Figure 3) is a 924 Turbo unit (931.107.221.01) installed on a late 356. This unit works well for all 356
and 912 applications, due to the exact breather hose diameter mating. The top hose is one half of a 944 coolant hose (944.106.245.01) used for its tightly bent angle. This hose is normally used
to join the radiator to the coolant reservoir. The middle hose is a standard 22 mm breather hose. A 12 mm thread insert has been pressed into the center of the bottom tank fitting. A CIS injection
fitting with a 7mm barb is then installed. A 7mm breather hose is attached and run from the tank to the oil dipstick tube. The oil dipstick now lives in the factory holder between the oil filter and
coil. On a 912 application the dipstick would remain in its factory location and oil would return via the vent in the right cylinder head.
These separators serve a dual purpose on engines that utilize carburetors. Normally a breather would be attached from the engine directly to the air cleaner, allowing the thick oil vapor to enter the
carburetor and travel to the float bowl and to its air correction jets. This can cause poor running and unnecessary carburetor maintenance. With this modification, the air cleaner fitting should be
installed directly above the carburetor velocity stack. This will draw the pure vapor through the carburetor and not contaminate the entire carburetor fuel system. This extends service intervals.
P.S. This modification also works well for cars that are not raced but just use oil because they have blow-by from age. These separators will remove the oil from the blow-by and return it to the
engine case. The fuel/exhaust portion of the blow-by gas will then be re-burnt as it enters the intake system, greatly reducing overall oil consumption.
Parts List
JAZ Oil breather tank with 12AN fitting #605.225.01-$53.95
930.107.321.01-930 Oil separator--$64.10
931.107.221.01-931 Oil separator--$73.55
944.106.245.01-944 Coolant hose--$23.98
944.106.241.03-944 coolant elbow--$6.00
911.125.341.01-911SC vacuum fitting--$20.68
Good Luck!
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