Chapter 2 ：Subaru High Power Engine Pedigrees. The history of the masterpiece Subaru “EJ20” engine

Chapter 1 we have adopted the flat 4-cylinder type from the days of Subaru 1000, but we have reported that its superiority is utilized in car making and also in terms of safety. I also looked at the advantages and benefits of the engine structure.

The secret of boxer sound

The EJ engine for the first generation Legacy was planned as a flat 4-cylinder engine that covers displacements from 1.5L to 2.5L. The goal was to achieve a world-leading high output with 2.0L.

Therefore, with a displacement of 1944 cc, the bore stroke is 92.0 mm × 75.0 mm, it is a big bore / short stroke, and the intake and exhaust valve is a large diameter 4 valve in order to thicken the intake and exhaust port, etc. It achieves a high rotation speed of 7500 rpm by the high-power engine design method. The intake manifold is equipped with a low-speed / high-speed switchable variable intake system.

Since a large-diameter valve is used for straight intake, the valve holding angle is as wide as 52 degrees, and since a convex piston is used, it becomes a deformed combustion chamber and is not a uniform shape, so cooling loss is large.The valve drive is DOHC and the rocker arm type of the inner fulcrum is used to maximize the valve lift. As a result, both the naturally aspirated and turbo have achieved the highest output in the 2.0L class.

Finally, in order to adapt to high power, the crankshaft finally adopts a 5-bearing type to support high speed and high power. Therefore, the crank web has a very thin shape. The metal journal is mirror-finished to withstand high loads.

The SOHC EJ type cylinder has an open deck structure with the cylinder top open, but the DOHC EJ20 type has a high-strength, high-rigidity closed deck (the cylinder top is closed except for the waterway), although productivity is poor. For example, it has been adopted to make it suitable for high-power engines. Furthermore, the left and right each 2cylinders each employ a cross flow cooling system. The normal four cylinders are of the vertical flow type, and the cross flow is excellent for uniform cooling between the cylinders.

The intake manifold is of equal length, but the exhaust manifold is an unequal length manifold that collects every two cylinders on one side.For this reason, it produces a unique exhaust sound that is similar to the rumble sound of a V8 engine at low speeds, which is a major feature of the early model EJ20 engine.


Natural racing engine

The early EJ20 turbo engine adopted the IHI RHB52 turbo. In order to have a smoother torque characteristic, the supercharging pressure is set to a low value of 0.6 bar, which is quite different from the later high supercharging pressure EJ20 turbo engine.

naturally aspirated specifications engine is 150ps / 6800rpm, 172Nm / 5200rpm , the turbo specification engine, which is the favorite of high power type, achieved 200ps / 6000rpm, 260Nm / 3600rpm in combination with a water-cooled intercooler. Then, the RS-RA was set on the sedan as a model to be used for rallies, and the dedicated EJ20 turbo was installed.

Although the output of this special engine was 220ps, it was balanced by STI, mirror-polished inside the intake port, adopted a forged piston, etc., and equipped with a gold-painted engine cover. Based on this engine, the Legacy Sedan RS-RA challengd the World Rally Championship (WRC).

In this way, the EJ20 engine achieved class-leading high power, and at the same time, it had a pedigree of being a high-power engine that was also intended for use in motor sports.

EJ20 type engine for Impreza WRX

The C segment Impreza (GC / GF type) series debuted in 1992 as the second global strategic car following the Legacy. Equipped with this IMPREZA series was the EJ engine series, which had a newly designed 1.5L engine and six engine types from 1.6L to 2.0L.

This is the first Impreza sports model, with the WRX set for entry into the World Rally Championship (WRC) and equipped with the EJ20 turbo. However, three years after the introduction of the first Legacy model, the EJ20 model for the Impreza WRX has been greatly improved.

It is a newly designed cylinder head part. For higher power and big torque, the DOHC valve drive has been changed from the conventional rocker arm type to a direct type with less friction resistance and higher rigidity, and the valve holding angle is changed from 52 degrees to 41 degrees, which is slightly narrowed. By doing so, the combustion chamber is made compact.

The turbocharging pressure has been increased to 0.8bar. Furthermore, the intercooler has been changed from a water-cooled type to an air-cooled type with a larger capacity to improve the intake cooling performance. For this reason, an air intake for the intercooler has been newly installed on the hood from WRX. In addition, the WRX RA, which is the base of the rally car, is also equipped with a water spray for forced cooling of the air-cooled intercooler. This is to obtain FIA approval for use in the rally.

With such a big design change, the output of EJ20 turbo can generate 240ps / 6000rpm and maximum torque 304Nm / 5000rpm.

Then, in 1994, based on the Impreza WRX RA, STI adopted a forged piston, equipped with an EJ20 type turbo that was tuned specifically for balancing etc. “WRX STi” (STi notation at that time) was set Has been done.

This Impreza WRX RA was able to achieve the feat of participating in the World Rally Championship series from 1993 as planned and winning the WRC championship for three consecutive years from 1995. Its power train, the EJ20 turbo engine, proved its high potential in the rally motorsport field, and Subaru won the best in the world Chanpion.＜text：Haruhiko Matsumoto＞

＜chapter3＞

＜chapter1＞

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