Subaru FB25 Engine
|Manufacturer||Gunma Oizumi Plant
|Also called||Subaru FB25
|Cylinder block alloy||Aluminum|
4 valves per cylinder
|Piston stroke, mm (inch)||90 (3.54)|
|Cylinder bore, mm (inch)||94 (3.70)|
|Displacement||2498 cc (152.4 cu in)|
|Power output||127 kW (172 HP) at 5,800 rpm
129 kW (175 HP) at 5,800 rpm
|Torque output||236 Nm (174 lb·ft) at 4,100 rpm
235 Nm (173 lb·ft) at 4,000 rpm
|HP per liter||68.9
|Weight, kg (lbs)||–
|Fuel consumption, L/100 km (mpg)
|Subaru Forester 2.5
|Turbocharger|| Naturally aspirated
|Oil consumption, L/1000 km
(qt. per miles)
|up to 1.0
(1 qt. per 600 miles)
|Recommended engine oil||0W-20
|Engine oil capacity, L (qt.)||4.8 (5.1)
|Oil change interval, km (miles)||5,000-10,000
|Normal engine operating temperature, °C (F)||–|
|Engine lifespan, km (miles)
-No life span loss
|The engine is installed in||Subaru Forester
In 2010 they released 2.5-liter FB25 motor for the large Subaru cars. This motor is a successor of naturally aspirated flat-4 boxer EJ253 engine. Its basis is aluminum FB20 cylinder block with cast-iron sleeves, diameter of cylinders in it was increased to 94 mm, thickness of cylinder block sidewalls was 3.5 mm. New pistons were installed in the cylinder block, they had slightly modified skirts for friction drop. The compression ratio was lowered to 10.
As well as all flat-4 engines, FB25 uses two heads. These heads are equipped with two camshafts and use 4 valves on the cylinder and roller rocker arms. These cylinder block heads use variable valve timing system Dual AVCS on all camshafts. These camshafts are set in motion with the help of non-supervised timing chain.
Being compared to EJ25, this motor has got the changed cooling system, it works better now.
Fuel injectors were removed from intake manifold and placed in cylinder block head, and injection system itself became much more complex and perfect. The exhaust system was completely changed and improved.
This motor shows 172 HP at 5,800 rpm, and torque 236 Nm at 4,100 rpm.
In 2014 they slightly modified FB25. Thickness of cylinders sidewalls decreased to 3.2 mm, new pistons were installed, compression ratio was increased to 10.3. Also intake ports were improved, intake valves were increased to 36 mm, the exhaust manifold and exhaust pipe were modified, the whole exhaust system became easier. New ECU was installed on this motor.
Capacity of FB25 increased to 175 horsepower at 5,800 rpm, and torque 235 Nm at 4,000 rpm.
FB25 firing order is 1-3-2-4.
Subaru FB25 engine problems and malfunctions
Unlike FB20, this 2.5-liter motor had no problems with a high oil consumption. The rest problems of FB25 are the same as FB20. HERE you can learn more about them.
You should not dream of building FB25 turbo, it was created for different purpose. In order to get reliable motor and receive additional capacity, purchase aftermarket cat-back exhaust system and adjust ECU more aggressively. It will allow to receive about 190 horsepower and classical Subaru sound.
If this capacity is not enough for you, then purchase Subaru WRX, as it is senseless to improve FB25.