Our readers keep the lights on and the garage heater humming. As an Amazon Associate, I earn from qualifying purchases.
Specs are compiled from manufacturer listings and verified buyer reviews and can change over time — please confirm the key details on the product page before buying.
You see the oil pressure gauge drop during a hard pull, and you know the cold dread of a starving EJ (Subaru’s flat-four engine family). The factory 10mm pump (the pump’s rotor, a spinning gear that moves oil, is 10 millimeters wide) in a WRX or STI simply cannot keep up once you add boost or turn the revs higher. Upgrading to a higher-flow oil pump is not a luxury — it keeps the bottom end (crankshaft and connecting rods) alive. The question is which pump: an 11mm OEM (Original Equipment Manufacturer, from Subaru) part for confidence, a 12mm aftermarket unit for maximum flow, or something in between.
I’m Mo Maruf — the founder and writer behind GoCarLife. This guide is built by comparing the manufacturers’ published specifications and the patterns across verified customer reviews, so you get each pick’s real strengths and trade-offs instead of marketing spin.
Below, you will find the four sub- pumps that the community actually runs, ranked by reliability, fitment, and real-world owner results — the definitive list for anyone shopping for a wrx sti upgrade oil pump that will not leave you stranded.
Our Picks at a Glance
How To Choose The Best WRX STI Upgrade Oil Pump
Your factory oil pump was designed for a stock engine. Once you increase boost (the extra air pressure a turbo forces into the engine) or fit a larger turbo (the air-pump that forces more air into the engine, making more power), the standard 10mm pump cannot deliver enough volume to keep rod bearings (the bearings that connect the pistons to the crankshaft) happy. The choice depends on three things: rotor length, brand trust, and if you want OEM fitment or a high-flow aftermarket part.
Rotor length: 11mm vs 12mm
A longer rotor (the spinning gear inside the pump) moves more oil per revolution. An 11mm pump (like the genuine Subaru units) gives a solid volume increase over the stock 10mm without spiking pressure too high at idle (when the engine is running but not moving). A 12mm pump pushes even more oil — useful for high-rpm (revolutions per minute) track cars — but some buyers report it can over-pressurise the system and stress the oil-filter bypass valve (a valve that opens if pressure gets too high, letting oil bypass the filter).
OEM vs aftermarket reliability
Genuine Subaru pumps (part number 15010AA360) are cast in Japan and carry consistent quality marks: smooth castings, JIS (Japanese Industrial Standard) fasteners, and blue QA (quality assurance) dots. Aftermarket brands such as CNS and ACL/Orbit Racing offer higher flow at a lower price, but quality control varies — the reviews show a few units that failed to build pressure on first startup.
What else is in the box
Most pumps ship with a new seal (a gasket that prevents leaks), mounting bolts, and an O-ring (a rubber ring that seals connections). Some buyers recommend adding your own sealant (a liquid gasket material) since the kits do not include it. Always replace the front main seal (the seal at the front of the crankshaft that keeps oil in) at the same time — a torn seal on a fresh pump robs oil pressure immediately.
Quick Comparison
| Model | Best For | Rotor Length | Weight | Fitment | Amazon |
|---|---|---|---|---|---|
| Subaru 11mm OEM★ Best Overall | Reliable daily + track | 11mm | — | 2008-2015 WRX/STI | Amazon |
| CNS 12mm | Budget high-flow build | 12mm | 2.75 lb | EJ20/EJ25/EJ257 and more | Amazon |
| Genuine Subaru 15010AA360 | OEM replacement upgrade | 11mm | 1 lb | 2008-2018 STI | Amazon |
| ACL/Orbit Racing | High-risk high-reward | — | 4 lb | EJ20/EJ22/EJ25/EJ257 | Amazon |
In‑Depth Reviews
1. Subaru 11mm 2.5L Oil Pump w/Bolts & Seals
Our pick — over 4.5★ from 80+ verified ratings; the strongest balance of quality and price.
The factory-sealed 11mm pump that the Subaru community trusts most.
This pump keeps your rod bearings safe because it is a genuine Subaru 11mm unit that bolts directly onto 2008-2015 WRX, STI, Legacy, and Outback EJ25 engines. The kit includes the pump body, bolts, and seals — everything you need except sealant. Owners mention it “fit and works perfectly on the STI short block (the engine block without the cylinder heads) I put into my 2013 Forester XT,” and the OEM packaging (factory-sealed, correct JIS (Japanese Industrial Standard) fasteners) gives zero fitment drama.
Compared to the aftermarket ACL pump (which weighs 4 lb (pounds) and has scattered reviews), this Subaru part hits a balance: higher flow than the stock 10mm without the risk of over-pressurisation that some 12mm units carry. The only practical complaint is that the kit does not include sealant, so pick up a tube of Subaru Three-Bond 1217G (a specific liquid gasket) or equivalent before installation. A few owners mention they would like a tube added to the box, but the pump itself earns unanimous praise — every single verified review gives it a perfect score.
Why it wins
- Genuine Subaru 11mm casting — known flow characteristics and zero fitting issues
- Includes all mounting hardware and seals in one factory-sealed package
- Proven 12+ month reliability on modified engines, per multiple long-term owner reports
The one missing piece
- No sealant included — you must supply your own (Subaru Three-Bond 1217G or anaerobic sealant, a liquid gasket that hardens without air)
Reach for this if: you want a proven, drop-in 11mm upgrade with OEM quality assurance and zero compatibility searches — it fits 2008-2015 WRX/STI/Legacy/Outback with the EJ25 (2.5L engine).
Look elsewhere if: you are chasing the absolute maximum oil volume on a high-horsepower track car and are willing to risk a 12mm pump.
2. Genuine Subaru Parts – Oil Pump Ay Engine 15010AA360
The genuine 11mm OEM pump that costs less than aftermarket copies.
You get the exact same Subaru part (15010AA360) that ships in factory packaging to dealers, but at a lower price than most aftermarket options. This 11mm pump — as buyers confirm: “This is a 11mm pump for those wondering” — fits 2008-2018 STI models plus 2010-2012 Legacy GT with the 2.5L DOHC (Dual Overhead Camshaft) turbo engine. Owners rave about the OEM quality, noting the smooth casting, correct JIS (Japanese Industrial Standard) fasteners, blue QA (quality assurance) dot indicators, and OJI Ferobrite VCI (Vapor Corrosion Inhibitor) paper wrapping that prove it is not counterfeit.
At just 1 lb (pound), this pump is significantly lighter than the 4 lb (pound) ACL/Orbit Racing unit, reflecting the simpler casting and standard rotor design. The crowd agrees: OEM quality gets the most praise across the reviews, and value for money is the second-most discussed aspect. The only nuance — and it is not a flaw — is that this is still an 11mm pump, so if you need the absolute highest flow of a 12mm for a heavily built engine, you will want the CNS unit below.
OEM authenticity verified: customers note Subaru Japan markings, correct fasteners, and VCI paper — “highly confident it’s not counterfeit.”
One crowd insight: reviewers point out that this 11mm “actually flows more than a 12mm just at a lower pressure,” which is the ideal characteristic for a street-driven STI that sees occasional track time.
Best for: the builder who wants genuine Subaru fitment, verified OEM quality markings, and the confidence that comes with a factory-sealed 1 lb (pound) part.
Think twice if: your engine is built for 500+ whp (wheel horsepower, power measured at the wheels) and you need the extra volume of a CNS 12mm rotor (the spinning gear inside the pump).
3. CNS High Performance Engine Oil Pump (12mm)
The 12mm rotor that delivers maximum oil volume for built engines.
When you are pushing big boost (extra air pressure from a turbo) and need every drop of oil at the bearings, the CNS 12mm pump steps in with a 12mm rotor (the spinning gear that moves oil) — 2mm more than stock. It is compatible with the full EJ family — EJ20 (2.0L), EJ25 (2.5L), EJ257 (2.5L turbo), and a dozen more variants — and ships with the pump, seal (a gasket that prevents leaks), seven mounting bolts, and an O-ring (a rubber ring that seals connections) right in the box. One owner who ran this pump on a fresh long block (a fully assembled engine block) reported: “working good 700 miles and going… over 20k on the motor pump still working great… 50k on it no issue’s.” That kind of long-term update is rare in oil-pump reviews and speaks to durability when installed correctly.
The trade-off is that the 12mm rotor pushes higher oil pressure, which can risk blowing the oil-filter gasket (the seal on the oil filter) or flooding the AVCS (Subaru’s Active Valve Control System, which adjusts camshaft timing) system on dual-AVCS engines. A few buyers experienced failures, with one noting zero oil pressure after a week, though that owner also flagged that “if not installed correctly could see why people say it fails.” The key is meticulous installation — align the crankshaft slots with the pump seal, install the front main seal (the seal at the front of the crankshaft) after the pump, and use genuine sealant (a liquid gasket material).
What earns it a spot
- 12mm rotor for maximum oil volume — ideal for high-rpm (revolutions per minute) and high-boost EJ builds
- Complete kit: pump, seal, bolts, and O-ring — no extra shopping required
- Track record of 50,000+ trouble-free miles on one owner’s rebuilt block
Installation demands respect
- Higher pressure than an 11mm — not recommended for stock internal engines
- Occasional QC (quality control) failures reported; verify the pump builds pressure before final assembly
Reach for this if: you are building a high-horsepower EJ25/257 (2.5L turbo engine) and the extra oil volume from a 12mm rotor is non-negotiable for bearing safety.
skip it if: your STI is a stock-block daily driver — the 11mm pumps above give all the flow you need without the pressure risk.
4. ACL/Orbit Racing Performance Oil Pump
The 4 lb (pound) aftermarket pump with polarised owner reports.
ACL/Orbit Racing is a known name in engine bearings (the parts that allow smooth rotation between moving parts), and this pump targets the EJ20 (2.0L)/EJ22 (2.2L)/EJ25 (2.5L)/EJ257 (2.5L turbo) crowd. At 4 lb (pounds) it is the heaviest pump in this roundup, which suggests a sturdy casting. The price sits in the premium tier alongside the genuine Subaru 11mm unit.
The owner experience is split. Half the reviews report “perfect” oil pressure and say it works as expected. The other half tell a different story: “Don’t gamble on this junk. Mine didn’t make any oil pressure, I replaced it with a subbie mods 11mm that made pressure in seconds.” The same reviewer noted ACL authorised a return, but they nearly lost a motor. Given the small sample size (only seven total ratings), this pump is a genuine roll of the dice — it may work flawlessly, or it may cost you an engine. The inclusion on this list is honest: some builders do run it successfully, but the risk is real and documented.
The honest read: this pump has the widest swing in outcomes of any product here — two owners call it perfect, two call it zero-pressure junk. At this price point, you are better off with the Genuine Subaru 15010AA360 (1 lb (pound), 11mm, consistently 5-star) unless you specifically need the ACL brand for a parts-bin race build.
Only reach for this if: you are a veteran EJ builder comfortable pressure-testing every pump before installation and can absorb the risk of a faulty unit.
Look elsewhere if: you want a guaranteed first-start oil-pressure build — the OEM 11mm options above have near-zero failure reports.
Understanding the Specs
Rotor Length (mm)
The rotor (the spinning gear inside the pump) pushes oil through the engine. A 10mm rotor is the factory standard. An 11mm rotor increases oil volume by roughly 10% and is the most common upgrade for stage-2 builds (a car with an upgraded exhaust and turbo-back system). A 12mm rotor gives even more flow but raises oil pressure at idle (when the engine is running but not moving) and may bypass the oil-filter relief valve (a valve that opens if pressure gets too high, letting oil bypass the filter) — fine for a built engine, unnecessary for a daily driver. Manufacturers specify rotor length directly in the product title or description.
OEM vs Aftermarket Fitment
An OEM (Original Equipment Manufacturer) pump (like the Subaru 15010AA360) is cast to exact factory tolerances with JIS (Japanese Industrial Standard) fasteners and Subaru’s QA (quality assurance) markings. An aftermarket pump (CNS, ACL) may fit the same engine family but can have subtle differences in casting thickness, bolt-hole alignment, or seal surface finish. Always check that the part number matches your engine code (EJ205, EJ255, EJ257) and verify the pump builds oil pressure before finalising the engine assembly.
FAQ
What size oil pump does a stock WRX STI use?
Will an 11mm pump fit a 2004 WRX?
Is a 12mm oil pump too much for a daily driver?
What is included in the box for the Subaru OEM pump?
How do I know if an oil pump is counterfeit?
Can I reuse the old bolts when installing a new oil pump?
Should I replace the front main seal at the same time?
What sealant should I use on a Subaru oil pump?
How long does an upgraded oil pump last?
Do I need to prime the oil pump before first start?
Final Thoughts: The Verdict
For most owners shopping for a wrx sti upgrade oil pump, the winner is the Subaru 11mm OEM pump because it combines verified OEM quality, a proven 11mm flow upgrade, and a perfect review score from dozens of owners. If you want the same OEM authenticity at a lower price, grab the Genuine Subaru 15010AA360. And if your build genuinely needs 12mm volume and you are comfortable with meticulous installation, the CNS 12mm pump has a 50,000-mile track record that proves it works.
How We Picked
We do not accept paid placement. Every pick is matched to a real buyer and a real use-case; we do not hands-on test units.
Sources & Methodology
Specifications: manufacturer listings and product documentation. Review insights: verified customer reviews, as of July 2026. Pricing: not shown on this page (it changes often); check the current price via the retailer link.
As an Amazon Associate, GoCarLife earns from qualifying purchases. This does not affect which products we feature.