Oil Pump Part Numbers and differences

[Sgt.Gator]

We are prototyping and testing some mods to the Subaru oem pumps which has got us going thru many of the available pumps on the market, both oem and aftermarket.

There has been considerable confusion related to the 10mm pumps and their case markings. Also it is widely believed all Subaru EJ pumps have 78mm rotors, but they do not.

 

The 10mm 15010AA300 has a 78mm outer rotor.

The newer model 10mm 15010AA320 has a 76mm outer rotor.

 

The 10mm 15010AA300 is marked with "10" on the outside and inside.

The 10mm 15010AA320 is marked with a "76" on the outside and inside.

Both of these 10mm pumps are still available today.

 

Also of note:

The 11mm 15010AA360 is marked with "78" and has a 78mm rotor.

The JDM 12mm 15010AA310 is marked with a "12" and has a 78mm rotor.

 

So it's not nearly as illogical or confusing as many people would have you think that the 10mm comes marked as either a "10" or a "76" and are identical. They are not, the rotor diameters are different, the part numbers are different. However the pump performance specs appear to be the same.

 

So why would Subaru switch the new pump to a 76mm, but keep the 78mm for the new 11mm? We wondered a great deal about that. I think we found the answer in a couple of SAE papers. Japanese engineers discovered that if you keep the same number of gear "teeth", the same depth of the "teeth", but fit them on a smaller rotor, it takes less TQ to drive the pump and have the exact same volume/pressure.

A few excerpts:

"Energy loss attributable to oil pumps accounts for approximately 10% of the total engine energy loss in the case of an engine lubrication oil pump."

"Given the same theoretical displacement, drive torque decreases with decreasing outer rotor outside diameter, due to a decrease in the loss caused by frictional resistance (Fig. 6). In sum, reduction in rotor radial size is most effective for drive torque reduction."

 

It seems the smaller rotor is simply more efficient, runs cooler, less friction, better gas mileage, a bit more HP to the wheels (very bit since we are only talking 2mm size difference).

 

So why did they keep the 78mm rotor for the 11mm pump? I don't know for sure. My best guess is the 11mm is only used on the DAVCs engines which is a limited market volume, so the least expensive path was to reuse the 78mm rotor tooling with wider 11mm rotors. But there's more differences coming in another post soon.!

 

And as a note the FA20F engine uses a 77mm x 14mm rotor with more "teeth". It's difficult to compare performance specs between the EJ pumps and the FA pump because the FSM has typically used an oil temp of 176 degrees F at either 5,000 or 6,000 rpm, but the FA20F uses a temp of 248 degrees F at 6,700rpm. One interesting spec difference is the relief valve pressure in the FA20F is 102psi.

Gator - Colonel Red Racing

Edited December 21, 2020 by Sgt.Gator
Additional Info

[rhino6303]

That's some good knowledge given. I quickly looked back at my orders for my current setup to see if I bought the 300 or 320 pump. I do have the 300. I'm curious to hear your thoughts on why 76 vs 78 when you do share.

[boxkita]

Dry sump for a DD?

[Sgt.Gator]

That's some good knowledge given. I quickly looked back at my orders for my current setup to see if I bought the 300 or 320 pump. I do have the 300. I'm curious to hear your thoughts on why 76 vs 78 when you do share.

 

I've edited the first post!

 

Dry sump for a DD?

 

LOL, NO! If you want a dry sump in your daily driver buy a Corvette or a Porsche!

Edited December 21, 2020 by Sgt.Gator

[Sgt.Gator]

Both 10mm pumps and the 12 mm pump have a drain hole under the crank seal that leads back to the engine oil sump. You can see it here:

 

....

 

 

Note this isn't just a hole drilled thru, it's a cast part of the pump body, then drilled. It protects from seal blowout. Most domestic oil pumps have similar hole for same purpose. The Toyota 2JZ modders even open up this hole to increase the flow back, and a standard check if the front crank seal is leaking is to stick a piece of wire down the hole to clear blockages. I've never heard of anyone clearing the drain hole in a Subaru pump when replacing the crank seal.

 

Now the strange difference: Subaru eliminated the seal oil drain on the 11mm pump. And they didn't just not drill the hole, they actually changed the casting to eliminate where the channel runs:

 

....

 

Why? I have no idea! Apparently Subaru engineers determined that having a seal drain was not necessary, or possibly having one could lead to seal blow out if the PVC system clogged up and the crankcase experienced positive pressure? But why not change the 10mm too?