What an oil pump upgrade does and why WRX STI owners choose it

The stock oil pump on a Subaru WRX STI moves oil through the engine at a fixed rate based on engine RPM. An upgraded pump increases flow volume, meaning more oil reaches critical bearing surfaces faster and under higher pressure. This matters most if you've modified your engine — added boost, changed cam timing, or increased redline — because the factory pump was designed for factory power levels.

The OEM pump delivers roughly 60 PSI at 6,000 RPM on a stock engine. An upgraded pump like the Koyo or Amtec unit can push 80+ PSI at the same RPM, or maintain higher pressure across a wider RPM band. The practical benefit is reduced bearing wear during sustained high-RPM driving, track use, or boosted operation where oil starvation becomes a real risk.

This is not a modification most stock owners need. If your WRX STI is unmodified and you drive it on the street, the factory pump is adequate. The upgrade makes sense if you've tuned the engine, plan to, or regularly push it hard.

Key Takeaways

  • An upgraded oil pump increases flow and pressure, protecting bearings during high-RPM or boosted driving that the stock pump was not designed for.
  • The job requires removing the timing belt cover, timing belt, and crankshaft pulley, so budget 6 to 10 hours of labor or a full weekend if you do it yourself.
  • Koyo and Amtec are the two most common upgrades for the WRX STI, with Koyo being the more affordable option and Amtec offering slightly higher pressure.
  • You will need a timing belt tool kit, a crankshaft pulley holder, and basic metric sockets; renting or borrowing specialty tools is cheaper than buying them once.
  • The upgrade costs $300 to $600 for the pump itself, plus $800 to $1,500 in labor at a shop, or your time and tool rental if you do it at home.

Choosing between Koyo and Amtec pumps

Koyo and Amtec are the two pumps you will encounter most often in WRX STI forums and shops. Both bolt directly to the crankshaft in place of the OEM unit and require no modification to the engine block or oil pan.

The Koyo pump is the more common choice. It flows about 15 to 20 percent more oil than stock and costs less — typically $350 to $450. It is reliable on engines making up to 400 wheel horsepower and handles track days without issue. The trade-off is that pressure rises more gradually with RPM, so at low idle you may not see a dramatic difference.

The Amtec pump is more aggressive. It delivers higher pressure across the entire RPM range and flows slightly more volume than the Koyo. It costs more — usually $500 to $650 — but is the choice for heavily modified engines or those running sustained high boost. Some owners report slightly noisier operation at idle, though this is not universal.

For a moderately tuned engine (300 to 350 wheel horsepower), the Koyo is sufficient and saves money. For aggressive builds or if you plan future modifications, the Amtec is the safer choice.

Tools and parts you will need

Removing and installing an oil pump on a WRX STI is not a bolt-on job. You must remove the timing belt to access the pump, which means you need timing belt tools. Here is what to gather before you start:

  • Timing belt tool kit — includes crankshaft and camshaft locking pins, and a belt tensioner tool. Rent this from a tool library or auto parts store for $30 to $50 rather than buying it.
  • Crankshaft pulley holder — a specialized socket or strap wrench that holds the pulley still while you remove the center bolt. Rental is $10 to $20.
  • Metric socket set — you will need 17mm, 19mm, and 22mm sockets at minimum.
  • Torque wrench — critical for the crankshaft pulley bolt (92 to 112 foot-pounds) and timing belt tensioner bolts.
  • New timing belt — while you have the cover off, replace the belt if it has more than 60,000 miles on it. A new belt costs $80 to $150 and saves you from doing this job twice.
  • Gasket sealer and new gaskets — the timing belt cover gasket and oil pump gasket should be replaced. Use Subaru OEM gaskets or quality aftermarket equivalents.
  • Fresh oil and filter — you will drain the pan to remove the pump, so plan to refill with new oil.

The removal and installation sequence

The job follows this order: drain oil, remove the timing belt cover, lock the crankshaft and camshafts, remove the timing belt, remove the crankshaft pulley, unbolt the pump, install the new pump, and reassemble in reverse. The entire process takes 6 to 10 hours the first time.

Start by draining the oil into a pan. Remove the plastic undertray if your car has one. Unbolt the timing belt cover — there are usually six to eight bolts around the perimeter. Once the cover is off, you can see the timing belt, crankshaft pulley, and the pump bolts at the bottom of the crankshaft.

Use the locking pins from your timing belt kit to lock the crankshaft at top dead center and the camshafts in their neutral position. This prevents the valves from moving while you work. Remove the crankshaft pulley bolt using the pulley holder to keep it from spinning. The bolt is tight — expect to use significant force or a breaker bar.

Remove the timing belt. Unbolt the pump from the crankshaft — there are usually three bolts. Lift the old pump straight out. Clean the mounting surface on the crankshaft with a rag and gasket scraper to remove old gasket material.

Install the new pump with a fresh gasket, torque the bolts to the specification in your pump's instructions (typically 15 to 20 foot-pounds), and reinstall the timing belt. The belt tension is critical — use the tensioner tool to set it to the correct specification, usually checked with a belt tension gauge. If you are unsure, have a shop verify the tension before you close everything up.

Timing belt tension and why it matters

The timing belt synchronizes the crankshaft and camshafts. If the tension is too loose, the belt will slip and the engine will lose timing, causing rough running or no start. If it is too tight, you will wear out the belt and bearings prematurely.

Subaru specifies belt tension using a deflection method or a tension gauge, depending on your model year. A deflection check means pressing on the belt midway between two pulleys and measuring how far it moves — typically 0.3 to 0.4 inches. A tension gauge gives you a direct PSI reading, usually 110 to 130 PSI for a WRX STI.

If you do not have a tension gauge, the deflection method is acceptable, but it is less precise. Many shops will check and adjust the tension for $50 to $100 if you ask them to verify your work before you drive the car. This is money well spent — a timing belt that slips can cause internal engine damage.

What to expect after installation

Once you have reassembled everything, fill the engine with fresh oil and run it at idle for a few minutes. Watch the oil pressure gauge — it should climb to 40 to 60 PSI at idle and stay there. If pressure is lower than before, you may have an air pocket in the system; run the engine at 2,000 RPM for a minute to bleed it out.

Take the car on a short test drive at moderate RPM before pushing it hard. Listen for any new noises from the timing belt area. A slight whine at startup is normal as the pump primes; a grinding or squealing sound means something is wrong and you should stop and investigate.

After 50 miles, check the oil level again and look under the car for leaks around the pump gasket or timing cover. If everything is dry and the pressure is stable, you are done. The upgrade will not change how the car feels on the street, but it will give you peace of mind during track days or sustained high-RPM driving.

When to do this upgrade alongside other work

Because the timing belt must come off, this is the ideal time to replace the belt itself if it is due, replace the water pump (which is driven by the timing belt), or inspect the cam seals and crankshaft seals. Doing these jobs together saves labor hours compared to doing them separately.

If you are planning a turbo upgrade, engine tune, or cam swap, do the oil pump upgrade at the same time. You will have the timing belt cover off anyway, and the new pump will be ready for the added stress of modifications.

If your car is stock and you are only doing the pump, you can skip the water pump and belt replacement unless they are due based on mileage. Check your owner's manual for the recommended interval — most WRX STIs need a timing belt change at 105,000 miles.

Frequently Asked Questions

Can I upgrade the oil pump without removing the timing belt?

No. The pump is bolted directly to the crankshaft behind the timing belt, and there is no way to access it without removing the belt and crankshaft pulley. Any shop that claims otherwise is cutting corners and risking timing issues.

Will a new oil pump make my WRX STI faster?

No. An upgraded pump does not add horsepower or change how the engine performs. It protects bearings and allows the engine to handle higher power safely. You will notice the benefit only if you are pushing the engine hard or have modified it.

How long does the pump last?

A quality aftermarket pump like Koyo or Amtec will last the life of the engine if maintained properly. Keep your oil clean and change it on schedule. The pump itself has no wear items and does not need service.

What happens if I ignore oil starvation and do not upgrade?

On a stock engine, nothing — the factory pump is adequate. On a modified engine running high boost or high RPM, bearing wear accelerates and you risk catastrophic engine damage. The pump upgrade is insurance, not a performance mod.

Can I do this job in my driveway without a lift?

Yes, but it is uncomfortable. You will be working under the car and reaching up into the engine bay. A lift or ramps make the job much easier and safer. If you use ramps, chock the rear wheels and use jack stands under the frame for safety.