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The Truth Behind The Subaru EJ-Series Engines - Tech-Knowledge

Are they as weak as tuners claim?

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Once known simply as the automotive company that built modest commuter cars like the Brat ('78 to '87), Subaru (a division of Fuji Heavy Industries) became internationally known for their boxer engines. Beginning in 1989 and continuing through to the present day, Subaru's horizontally opposed EJ-series motors are the mainstay engines of their model lineup, with all EJ-series engines sharing a 16-valve, flat-four horizontal configuration with displacements ranging from 1.5 to 2.5 liters. So why has Subaru continued their love affair with the boxer engine?

Utilizing a boxer engine configuration similar to what was once used in older-model Volkswagens, Subaru has continued use of the boxer engine with good reason. The Subaru boxer engine is a unique engine that's anything but typical. Engineer Karl Benz patented the flat-four engine in 1896. In 1971, inspired by airplane engine design, Fuji Heavy Industries, through the Subaru brand, released their interpretation of the flat-four. Because the engine was configured to be inline with the transmission it had a lower center of gravity to help minimize body roll in comparison to inline-four and V-type engines, which have a higher center of gravity and are prone to side-to-side vibration. This design provided a lighter weight and compact, economic design for Subaru. In all, there have been 23 engine variations of the EJ motors, including the '11 WRX STi model that develops 305 hp and 290 lb-ft of torque.

Subaru engines have always been known to be well engineered that are both powerful and torquey, but Subaru engineers left a lot to be desired when it came to the EJ205 ('02 to'05 USDM WRX), EJ255 (USDM WRX '06 to present) and EJ257 ('04 to'07 USDM WRX STi) turbocharged models. This month, we get in-depth with three of the top Subaru tuners in the world, as they help dispel myths and speak their minds about the infamous EJ-series engine.

Yimi Sport Tuning of Santa Clarita, CA, has been serving the Subaru community since 2003 as a one-stop shop for enthusiasts of all makes with parts, installation, and tuning, and also custom fabrication and welding services. Yimi Sports not only caters to customer cars but are avid participants at various road race events such as Super Lap Battle and Import Tuner EVO vs. STi Shootout, including this year when they took home the title of fastest Subaru.

Q: Focusing on the EJ205, EJ255, and EJ257 engines, there's been a lot of debate on their strengths and weaknesses and how they were never designed to handle an elevated horsepower level. Is there a secret recipe that can better educate Subie owners on how to build their engines to increase horsepower output and longevity?

A: The EJ-series motors are good motors, and we would not call them "weak" per se. On a stock motor, the two primary weaknesses are the stock cast hypereutectic pistons and oiling to the rod bearings. The pistons (particularly on the EJ255 and EJ257) will crack if subjected to knock/detonation events. Obviously, with proper ECU tuning the engine can be kept away from the knock threshold, making the pistons not as much of an issue.

Oiling to the rod bearings is the other primary issue. We typically don't see very many problems with the EJ255 and EJ257 in this respect, but do see it more on the older EJ205. Fundamentally there isn't a big difference between the 2.0L and 2.5L motors in terms of the design of the oiling system but the EJ205 is at least 5 to 9 years old now and some have not been treated to regular maintenance with quality fluids. From the factory, the allowable range of bearing clearance is pretty broad and if you don't use quality synthetic oil and change it often it can lead to problems. The same can be said of any motor, so while not a strong point of the EJs, it should not be painted as a "bad motor" because of it.

We don't believe in "secret formulas," but rather common sense. In the case of making EJ motors last, it boils down to proper ECU tuning by a reputable tuner who clearly understands the logic of the ECU and its interaction with the engine, along with regular maintenance and using quality fluids in the car.

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1 comments
hercules1909
hercules1909

How are you suggesting going into the 500whp range without sleeves. almost all of the ej25 blocks that get in there cracked the sleeves even at lower horsepower with very good tunes . why do you suggest this?

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