45° between cylinder banks. The 201A was 60° between cylinder banks; 45° later proved to be significant when EMD subsequently adapted the road switcher concept for most of its locomotives, and which required the narrower (albeit taller) engine which 45° provides. The 710, 645, and 567 are the only two-stroke engines commonly used today in locomotives. The engine is a uniflow design with four poppet-type exhaust valves in the cylinder head. For maintenance, a power assembly, consisting of a cylinder head, cylinder liner, piston, piston carrier, and piston rod, can be individually and relatively easily and quickly replaced. The block is made from flat, formed and rolled structural steel members and steel forgings welded into a single structure (a "weldment"). Blocks may, therefore, be easily repaired, if required, using conventional shop tools. Each bank of cylinders has an overhead camshaft which operates the exhaust valves and the unit injectors. The 567 is laid out with engine accessories (oil and water pumps and governors) at the "forward" end and the power take off at the "rear" end. The blowers and camshafts are at the "rear" end of the engine, with the blowers mounted above the power take off. All engines have mechanically-controlled unit injectors (patented in 1934 by General Motors, EMD's former owner). All 567 engines utilize forced induction, with either a Roots blower or a turbocharger. The turbocharger (a combination turbo-compressor system) follows EMD's innovative design that uses a gear train and over-running clutch to drive the compressor rotor during low engine speed, when exhaust gas temperature (and, correspondingly, heat energy) alone is insufficient to drive the turbine. At higher engine speeds, increased exhaust gas temperature is sufficient to drive the turbine and the clutch disengages, turning the turbo-compressor system into a true turbocharger. The turbo-compressor can revert to compressor mode momentarily during demands for large increases in engine output power. While more expensive to maintain than Roots blowers, the turbocharger significantly reduces fuel consumption and emissions, while improving high-altitude performance. Additionally, EMD's turbo-compressor can provide a 50 percent increase in maximum rated horsepower over Roots-blown engines for the same engine displacement. Output for naturally aspirated engines (including Roots-blown two-stroke engines) is usually derated 2.5 percent per above mean sea level. Turbocharging effectively eliminates this derating. Modifications 567AC engines (an "A" block upgraded to "C" block specifications) and 567BC engines (a "B" block upgraded to "C" block specifications), both of