Fixing the Evo Oil system - by Prosport Auto

We all know that the oil pump is the weak point of the 4G63 engine. Jafromobile has outlined the main issues with the oil pumps, front covers and oil filter housings in his very informative video's on youtube (

Road racing or circuit racing in the Evo platform always results in oil surge on right-hand (RH) corners, especially on corner exits. Regardless if you're using a larger oil pan (Racefab/AMS/Moroso), it still happens as you can't physically keep enough oil in the pan on the right-hand side of the engine and around the pickup. This is compounded with decent amounts of lateral and longitudinal grip (i.e. semi slicks and slick tyres) and high engine RPM.

AMS and Racefab extended sumps. Better than OEM but still not a complete solution for eliminating oil starvation.

So - what's wrong with the factory oil system?


The factory oil pump has the capacity to pump *too much oil*.

This is shown by the regulator opening around 2500-3000rpm. What the oil pump essentially becomes is a transfer pump. Lets say at 6000rpm, 50% of the oil goes to the engine and 50% of the oil is dumped out of the regulator. That 50% of oil that's dumped is dumped into the back of the sump, so it can never get back to the pickup during heavy corning (RH) or acceleration. This is the main problem. You're just transferring the oil away from where it needs to be. Even if you have a 10 litre oil pan, you're still pumping the oil away from the pickup. 

My idea is to reduce that problem. Any *excess* oil pumped by the oil pump is then dumped back to the front-right side of the sump. With acceleration and RH cornering forces, the oil can then go back to the pickup. Previously there is no way it will get back to the pickup. This is why the English Racing underdrive gear works well. It reduces the amount of oil the pump can flow, which then reduces the amount of oil dumped out of the regulator. 

To give you an idea on flow - the oil pump pushes around 12cc of oil every engine revolution. So at 3000rpm engine speed it's around 36 litres per minute. At 9000rpm it's around 108 litres per minute.
This is assuming 100% efficiency (which it wont be) and it's calculated off the oil pump gear tooth volume.

Oil pressure scatter graph from a sprited drive on the road showing the regulation system working.

Now that's we've covered the main problem - lets see what happens when you dont have enough oil at the pickup. The issue with getting dips in the oil pressure is not only damage to the engine. It's damage to the oil pump. Repeatedly pulling air into the oil pump slowly damages the housings which leads to larger tolerances and clearances. These bigger clearances then cause the oil pump to become less efficient and it can't generate oil volume and pressure correctly. I've seen this on cars with 80psi hot oil pressure at the start of a track day, by the end of the track day they are making 50psi. Not good.

Big damage to the oil pump for a range of reasons, the primary reason being oil surge (pumping air). Stiff aftermarket valve springs and cambelts combined with oil surge will quickly damage the oil pump. The main drive gear shaft is steel and the housing is plain aluminium. Once the oil film degrades it starts to destroy itself rapidly. Add some high RPM (9000+) use and it's a recipe for disaster.

Main drive oil pump gear is 33% faster than engine rpm.
Balance shaft (or stub shaft) is 100% faster (double) than engine rpm.

Keeping oil at the pickup

One of the main problems in the OEM oiling setup is the oil pressure regulator and how it's configured. When the oil pressure relief system sees oil pressure, it pushes on a sprung piston. When there is enough oil pressure, this piston is then pushed back to regulate the oil pressure by dumping any excess oil and pressure back into the pan. This is a key point. "Back into the Pan".

OEM dump port location. With heavy acceleration and right-hand corners, this dumped oil can never get back to the oil pickup. Combined with the high flow nature of the oil pump, this empties the oil pan and creates oil surge/starvation quickly.

Other OEM's fix this problem by making the dump port from the regulator to go straight back into the pump inlet. For packing reasons, Mitsubishi Engineers couldn't accomplish this.
Nissan RB pump left. Subaru EJ pump right.

The Racefab oil pan (made in NZ) is a great product for fast street cars. It's not a full solution for track-day or racing cars. This oil pan addresses the issues of fast right-hand corners with extra oil capacity on the front-right side of the oil pan. But this is quickly depleted (a couple of seconds), but it's certainly better than a stock oil pan.


The datalogs above are from a club-level car here in NZ. The track is Hampton Downs (National Circuit). T1, T2, T4 and T6 are all right-hand corners which highlights the weakness of the Evo oil pan + oil system design. Dropping to 30~35psi on every corner proves the pump is picking up air and will be causing damage to both the oil pump and the engine.

This data was collected on an Evo 5 using semi-slick and a Racefab Oil pan. Lap time is approx 1:12.5.

So - how do we fix it?

It's all in the oil pressure regulation system.

Our Infinite Evo oil pan will incorporate an external oil pressure regulator that dumps the oil in the correct place in the oil pan. This allows the "recycled" oil to get back to the pickup where the OEM system does not. There are also added benefits of being able to adjust your oil pressure depending on your engine and oil requirements, as these change when engine bearing clearances and systems (balance shafts) are modified.

Why use an external regulator?

Mitsubishi engineers just didn't have the space to build the system properly - for those who wanted to push their cars to the limit. The external oil pressure regulator is the only way to get the oil back to where it needs to be for sustained high g-force loadings.

But does it work?


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