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Factory Oil Pump

Genuine factory oil pumps for your engine rebuild. Available in 10mm, 11mm (MY08+ STI), and 12mm (JDM) pump gear rotor sizes. Rallispec high pressure modification is an optional service for high performance applications.

Usually ships within 2 to 3 days

Manufacturer: Subaru


  • Subaru EJ Engines

How do I select the proper oil pump for my application? Essentially the decision is dependent on making an evaluation of how quickly the oil will flow through engine bearings and any orifices such as piston oil sprayers and oil controlled variable cam systems. Larger oil clearances will increase the oil volume requirements in order to maintain oil pressure under high demand situations. Additionally, oil with a lower viscosity will flow more easily and require a higher volume oil pump due to the higher leakage rate. Temperature comes into play in two ways: first is that the viscosity of oil will drop off with increasing temperatures and second is that an aluminum engine block will expand with increasing temperature at a higher rate than the steel crankshaft resulting in an increase in oil clearance. A turbocharger will add to the thermal demands placed on the oil and there will be an associated drop in viscosity that comes with it.

One thing to take into consideration is that there will be additional parasitic losses driving a larger oil pump so it does not make sense to run a larger oil pump unecessarily. At moderate rpms a standard 10mm or 11mm oil pump will be more than adequate as pump output will exceed the demands of the engine for nearly all normal situations. The need for a high volume oil pump comes into play with a high performance engine at high rpms where the oil demands of the engine may be significantly higher than what the oil pump can supply and oil pressure may be declining to dangerous levels. The general rule of thumb is that an engine requires approximately 10psi per 1000rpm. Additionally, the crankshaft bearings farthest from the oil pump may actually be seeing much lower oil pressure than may be indicated on a guage (depending on the gauge location) and this must be taken into consideration. Although low rpm oil pressure is not usually a concern, if the pressure is too low during hot idle conditions it can starve the camshafts of oil and accelerate wear and therefore would justify running a high volume pump.

We suggest one size larger pump than stock for most street performance applications running our engines (which generally run 0.0005 - 0.0010in additional clearance over stock). Racing applications running our engines should use a 12mm oil pump to ensure sufficient margin of safety at high rpms. It may be necessary to use a 12mm oil pump when attempting to run a very lightweight oil at rpms and temperatures (such as a 0W20 or 0W30). But ultimately it will be a matter of evaluating the oil pressures under various operating conditions and deciding the most suitable pump to use. A high volume pump may create greater oil aeration and windage and it may be necessary to make other modifications to the oil system such as a large capacity baffled oil pan to allow the air more chance to separate out of the oil.

What is the high pressure modification? The high pressure modification involves shimming the oil pressure relief valve in order to raise the maximum oil pressure. It will only raise the maximum oil pressure, it will do nothing to raise oil pressures when oil demands are higher than pump output (and oil pressure is below the bypass valve cracking pressure).

Is the oil pressure enough to keep the crankshaft from touching down on the bearings under heavy loads? The oil pressure generated by the oil pump is only a small fraction of the oil pressure at the bearings when the crankshaft is rotating at speed. The pump pressure is to move the oil to where it needs to go and ensure a steady and constant supply of oil at all the locations that need it. The bearing oil pressures that support the engine loads are a result of hydodynamic forces. Basically the relative motion between the crankshaft journal and the bearing together with the viscous properties of the oil creates a high pressure wedge of oil to form and keep the journal and bearing separated. A heavy load will force the journal out of position and closer to the bearing surface which will compress the oil film which actually raises the hydrodynamic pressure to counteract the load. However, bearing housing distortion, surface imperfections, or geometric imperfections can result in journal to bearing contact under severe loads which is one of the reasons for increasing the oil clearances in a high output engine.