Engine Mechanical (WRX-STI): General Description: Specification

Engine	Model					2.5 L
	Cylinder arrangement					Horizontally opposed, liquid cooled, 4-cylinder, 4-stroke gasoline engine
	Valve system mechanism					Belt driven, double overhead camshaft, 4-valve/cylinder
	Bore X Stroke				mm (in)	99.5 X 79.0 (3.92 X 3.11)
	Displacement				cm³ (cu in)	2, 457 (150)
	Compression ratio					8.2
	Compression pressure (at 200 - 300 r/min)			kPa (kg/cm² , psi)	Standard	981 - 1, 177 (10 - 12, 142 - 171)
	Number of piston rings					Pressure ring: 2, Oil ring: 1
	Intake valve timing			Open	Max. retard	ATDC 5°
					Min. advance	BTDC 47°
				Close	Max. retard	ABDC 65°
					Min. advance	ABDC 13°
	Exhaust valve timing			Open	Max. retard	BBDC 28°
					Min. advance	BBDC 72°
				Close	Max. retard	ATDC 32°
					Min. advance	BTDC 12°
	Valve clearance	mm (in)	Inspection value	Intake		0.20^+0.04_-0.06 (0.0079^+0.0016_-0.0024 )
				Exhaust		0.35±0.05 (0.0138±0.0020)
			Adjustment value	Intake		0.20^+0.01_-0.03 (0.0079^+0.0004_-0.0012 )
				Exhaust		0.35±0.02 (0.0138±0.0008)
	Idle speed (Gear shift lever is in neutral)		r/min	No load	Standard	700±100
				A/C ON	Standard	750±100
	Ignition order					1 → 3 → 2 → 4
	Ignition timing			BTDC/{r/min}	Standard	15°±10°/700

Belt tension adjuster	Adjuster rod protrusion amount				mm (in)	5.2 - 6.2 (0.205 - 0.244)
Camshaft	Bending limit				mm (in)	0.020 (0.00079)
	Cam lobe height	mm (in)	Intake		Standard	46.55 - 46.65 (1.833 - 1.837)
			Exhaust		Standard	46.75 - 46.85 (1.841 - 1.844)
	Cam base circle diameter			mm (in)	Standard	37.0 (1.457)
	Journal O.D.	mm (in)	Front		Standard	37.946 - 37.963 (1.4939 - 1.4946)
			Center, rear		Standard	29.946 - 29.963 (1.1790 - 1.1796)
	Oil clearance			mm (in)	Standard	0.037 - 0.072 (0.0015 - 0.0028)
	Thrust clearance			mm (in)	Standard	0.068 - 0.116 (0.0027 - 0.0047)
Cylinder head	Warping limit (Mating surface with cylinder block)				mm (in)	0.035 (0.0014)
	Grinding limit				mm (in)	0.3 (0.012)
	Standard height				mm (in)	127.5 (5.02)
Valve seat	Seating angle between valve and valve seat					90°
	Contacting width between valve and valve seat	mm (in)	Intake		Standard	0.6 - 1.4 (0.024 - 0.055)
			Exhaust		Standard	1.2 - 1.8 (0.047 - 0.071)
Valve guide	Clearance between the valve guide and valve stem	mm (in)	Intake		Standard	0.030 - 0.057 (0.0012 - 0.0022)
			Exhaust		Standard	0.040 - 0.067 (0.0016 - 0.0026)
	Inside diameter				mm (in)	6.000 - 6.012 (0.2362 - 0.2367)
	Valve stem outer diameters		mm (in)	Intake		5.955 - 5.970 (0.2344 - 0.2350)
				Exhaust		5.945 - 5.960 (0.2341 - 0.2346)
	Valve guide protrusion amount				mm (in)	15.8 - 16.2 (0.622 - 0.638)
Valve	Head edge thickness	mm (in)	Intake		Standard	1.0 - 1.4 (0.039 - 0.055)
			Exhaust		Standard	1.3 - 1.7 (0.051 - 0.067)
	Overall length	mm (in)	Intake			104.4 (4.110)
			Exhaust			104.65 (4.1201)
Valve spring	Free length				mm (in)	53.48 (2.106)
	Tension/spring height			N (kgf, lb)/mm (in)	Set	204.6 - 235.4 (20.86 - 24.00, 46.00 - 52.93)/36.0 (1.417)
					Lift	363.5 - 401.7 (37.07 - 40.96, 81.73 - 90.32)/26.7 (1.051)
	Squareness					2.5°, 2.3 mm (0.091 in) or less
Valve lifter	Outer diameter			mm (in)	Standard	34.959 - 34.975 (1.3763 - 1.3770)
	Valve lifter mating surface inner diameter			mm (in)	Standard	34.994 - 35.016 (1.3777 - 1.3786)
	Valve lifter and valve lifter mating surface clearance			mm (in)	Standard	0.019 - 0.057 (0.0007 - 0.0022)
Cylinder block	Warping limit (Mating surface with cylinder head)				mm (in)	0.025 (0.0098)
	Grinding limit				mm (in)	0.1 (0.004)
	Standard height				mm (in)	201.0 (7.91)
	Cylindricality			mm (in)	Limit	0.015 (0.0006)
	Out-of-roundness			mm (in)	Limit	0.010 (0.0004)
	Clearance between cylinder and piston at 20°C (68°F)			mm (in)	Standard	-0.010 - 0.010 (-0.00039 - 0.00039)
	Cylinder inner diameter boring limit (diameter)				mm (in)	To 100.005 (3.9372)
Piston	Piston grade point				mm (in)	38.2 (1.50)
	Outer diameter		mm (in)	Standard	A	99.505 - 99.515 (3.9175 - 3.9179)
					B	99.495 - 99.505 (3.9171 - 3.9175)
				0.25 (0.0098) OS		99.745 - 99.765 (3.9270 - 3.9278)
				0.50 (0.0197) OS		99.995 - 100.015 (3.9368 - 3.9376)
Piston pin	Degree of fit					Piston pin must be fitted into position with thumb at 20°C (68°F).
	Clearance between piston pin hole and piston pin			mm (in)	Standard	0.004 - 0.008 (0.0002 - 0.0003)
Piston ring	Piston ring gap	mm (in)	Top ring	Standard	0.23 - 0.28 (0.0091 - 0.0110)
			Second ring	Standard	0.37 - 0.52 (0.015 - 0.0203)
			Oil ring	Standard	0.20 - 0.50 (0.0079 - 0.0197)
	Clearance between piston ring and piston ring groove	mm (in)	Top ring	Standard	0.040 - 0.080 (0.0016 - 0.0031)
			Second ring	Standard	0.030 - 0.070 (0.0012 - 0.0028)
Connecting rod and connecting rod bearing	Bend or twist per 100 mm (3.94 in) in length			mm (in)	Limit	0.1 (0.0039)
	Thrust clearance			mm (in)	Standard	0.070 - 0.330 (0.0028 - 0.0130)
	Oil clearance			mm (in)	Standard	0.017 - 0.045 (0.0007 - 0.0018)
	Bearing size (Thickness at center)		mm (in)	Standard		1.490 - 1.506 (0.0587 - 0.0593)
				0.03 (0.0012) US		1.504 - 1.512 (0.0592 - 0.0595)
				0.05 (0.0020) US		1.514 - 1.522 (0.0596 - 0.0599)
				0.25 (0.0098) US		1.614 - 1.622 (0.0635 - 0.0639)
Bushing of small end	Clearance between piston pin and bushing			mm (in)	Standard	0 - 0.022 (0 - 0.0009)
Crankshaft and crankshaft bearing	Bending limit				mm (in)	0.035 (0.0014)
	Crank pin	Cylindricality		mm (in)	Limit	0.006 (0.0002)
		Out-of-roundness		mm (in)	Limit	0.005 (0.0002)
		Grinding limit (dia.)			mm (in)	To 51.734 (2.0368)
	Crank journal	Cylindricality		mm (in)	Limit	0.006 (0.0002)
		Out-of-roundness		mm (in)	Limit	0.005 (0.0002)
		Grinding limit (dia.)			mm (in)	To 59.742 (2.3520)
	Crank pin outer diameter		mm (in)	Standard		51.976 - 52.000 (2.0463 - 2.0472)
				0.03 (0.0012) US		51.954 - 51.970 (2.0454 - 2.0461)
				0.05 (0.0020) US		51.934 - 51.950 (2.0447 - 2.0453)
				0.25 (0.0098) US		51.734 - 51.750 (2.0368 - 2.0374)
	Crank journal outer diameter		mm (in)	Standard		59.984 - 60.008 (2.3616 - 2.3625)
				0.03 (0.0012) US		59.962 - 59.978 (2.3607 - 2.3613)
				0.05 (0.0020) US		59.942 - 59.958 (2.3599 - 2.3605)
				0.25 (0.0098) US		59.742 - 59.758 (2.3520 - 2.3527)
	Bearing size (Thickness at center)	mm (in)	#1, #3	Standard		1.998 - 2.015 (0.0787 - 0.0793)
				0.03 (0.0012) US		2.017 - 2.020 (0.0794 - 0.0795)
				0.05 (0.0020) US		2.027 - 2.030 (0.0798 - 0.0799)
				0.25 (0.0098) US		2.127 - 2.130 (0.0837 - 0.0839)
			#2, #4, #5	Standard		2.000 - 2.017 (0.0787 - 0.0794)
				0.03 (0.0012) US		2.019 - 2.022 (0.0795 - 0.0796)
				0.05 (0.0020) US		2.029 - 2.032 (0.0799 - 0.0800)
				0.25 (0.0098) US		2.129 - 2.132 (0.0838 - 0.0839)
	Thrust clearance			mm (in)	Standard	0.030 - 0.115 (0.0012 - 0.0045)
	Oil clearance			mm (in)	Standard	0.010 - 0.030 (0.00039 - 0.0012)
NOTE: OS: Oversize US: Undersize