This edition of The End Wrench introduces the Subaru 2.2 liter naturally aspirated (N/A) and 2.2 liter turbocharged horizontallyopposed overhead cam (OHC) engines. It reviews the mechanical features of these engines and the differences betweenexisting engines. It also covers the procedures used in diagnosing and overhauling these engines. A list of applicableImportant Notes and Cautions, Service Bulletins and Special Toolsis included at the end of this article. Always refer to the appropriate model year Subaru Service Manual and the applicable service bulletins for all specificationand detailed servicing procedures.

Cylinder Heads The 2.2L engine uses a crossflow cylinder head design similar to the 1800cc OHC engine. Better breathing is provided by the two intake and two exhaustvalves per cylinder which improves the intake and exhaust flow. Fine-tuned high velocity intake and exhaust ports are used. The dual intake and exhaust ports are siamesed to further improve intake and exhaust flow. The 2.2L engine uses a compact pentroof combustion chamber versus the bath- tub design of the 1800cc/2700cc Subaru engines. It has a centrally located sparkplug which provides the quickest, most efficient combustion with a uniform flamefront from the plug to the top of the piston. This, combined with the 30 degreevalve angle compliments the pentroof combustion chamber shape optimizing lowand medium speed torque. The cylinder heads are interchangeable left to right. The 2.2L turbocharged engine cylinder heads have been modified to withstand increased internal combustion pressures. The coolant passages have been changed tomatch the closed deck design of the crankcase. These heads are not interchangeablefrom side to side nor with the N/A engine cylinder heads. There are three holes in the right cylinder head for the turbo oil supply, oilreturn, and coolant return.