mounted on the bulkhead. The aluminum plenums channel air from the air cleaner to the carburetors. Under the carburetors lie a 4 to 1 exhaust manifold. M121 BI The newer W110 190 produced in the 1960s featured an updated version of the M121 engine. This version had an increase of over the original version horsepower while fuel consumption stayed the same at of premium fuel. The nose speed also increased to , an improvement from the original's . These performance increases were possible despite the new model's bodywork which was significantly heavier due to new safety implementations to the vehicle. M121 BII An updated version of the M121 engine, called the M121 BII, was produced for the Mercedes 190SL. The four-cylinder unit has a single overhead camshaft and is regarded as the progenitor of an entire family of engines. The engine developed at 5700 rpm. For the 190SL, acceleration to took 14.5 seconds, and the top speed was . This made the M121 BII one of the faster engines on the road in its day. The fuel economy of the M121 BII was . M121 BIX The newest version of the M121 engine was the M121BIX, which was designated as a 2.0-litre engine. Displacement increased from through a increase in bore from . The compression ratio was increased to 9.0:1. This engine also used a new Solex 38PDSJ carburetor. Combined, power was increased to at 5200 rpm and of torque was produced at 3600 rpm. The M121 BIX engine was produced from 1965 to 1968 for the Mercedes Benz W110 model series. Applications The M121 engine was first employed in the Mercedes Benz "Ponton" models such as the 180. The 190 models featured an updated version of the M121 which offered greater performance through variations in compression ratios and improved carburetor systems. Its use continued in the W110 "Fintail" 190c and 200. The M121 engine has also been used in trucks such as the Mercedes-Benz L319 which was produced in 1967. 1967 1956. Some Unimog off-road models also implemented the M121. References M121 Straight-four engines Gasoline engines by model