This is a must READ!

 

Let’s talk a “little” technical that could make your life easier. For the purpose of this discussion, it would help you to have the exploded diagram from either the Porsche Workshop Manual OR a copy from our website HERE

 

Around mid-1975, Porsche changed the design of their production oil pumps changing from a 36mm long pressure gear set to a 43mm set. The result was a potential increase in oil flow of approximately 18%. This increase in flow would cause the engine case to fill with oil when the pressure piston opened. The solution was to create the oil bypass system; where oil bleeding off the pressure relief piston/valve would be short-cycled i.e. bypassed back to the inlet side of the pump. This corrected the issues created by the increased flow. There is no specific date in terms of when this modification went into full production. I have seen early turbos and some 7R cases where the modification HAD NOT been performed. You must verify it yourself.

 

This leads us to the next mini-rabbit hole. The initial bypass port diameters (bores) that we saw were 8mm. The subsequent diameter was increased to 11mm. I suspect (personal opinion) the change from 8mm to 11mm was due to the 8mm being insufficient to keep up with the volume on bypass. MOST machine shops are drilling the bypass port diameter to ½” (12.7mm) which would be most desirable.

 

The spring assembly that is on the bottom facing upwards is the primary pressure relief piston/valve. This controls the maximum flow and pressure whenever the engine is running. The opening pressure of the piston with new parts will be around 60-65lbs. This will vary with the type of pump, consumers, and bearing clearances. When you start the engine cold and gradually bring up the rpms, the “dip” you see in the pressure gauge is the piston/valve cycling. IF THE ENGINE CASE has had the “bypass modification”, the excess oil flow will be short-cycled (bypassed) back to the INLET side of the pump.

 

The spring assembly that is horizontal below the #3 cylinder is the SAFETY pressure relief piston/valve; typically opening 20-25lbs after the pressure relief piston/valve. This prevents the system from sustained pressures above 80-90 lbs. The excess oil being relieved here, DOES empty into the case.

 

Our ported and polished pumps have a flow increase of 20%+; consequently, you MUST have the case bypass performed or our pump will fill your case with oil.