The Ford Model T used a sidevalve, reverse-flow cylinder head inline 4-cylinder engine. It was primarily a gasoline engine. It produced for a top speed of . It was built in-unit with the Model T's novel transmission (a planetary design), sharing the same lubricating oil. The T engine was known for its simplicity, reliability, and economy. The engine remained in production for many years, and millions of units were produced. The engine design's lifespan exceeded that of the Model T vehicle itself, with industrial, marine, and military applications extending its production run. The T engine is on the Ward's 10 Best Engines of the 20th Century list. Fuel choices and fuel economy The Model T engine was built as a gasoline engine. While not engineered specifically for multifuel ability, its simple, robust design allowed a modified engine to successfully run on a variety of combustible fuels including benzene, ethanol, or kerosene. According to Ford Motor Company, the Model T had fuel economy on the order of . Carburetor and fuel system The Ford Model T engine had one carburetor, a side-draft, single-venturi unit. Its choke and throttle valves were controlled manually; the latter was with a hand lever rather than a foot pedal. The carburetor had no accelerator pump. Various vendors supplied Ford with carburetors for the T engine, including Holley, Zenith, and Kingston. During most of the T's production run, its fuel tank was mounted to the frame beneath the front seat. Because Ford relied on gravity to feed fuel to the carburetor rather than a fuel pump, a Model T could not climb a steep hill when the fuel level was low. The immediate solution was to climb steep hills in reverse. In 1926, the fuel tank was moved forward and upward, under the cowl, behind the dashboard on most models, which improved the gravity feed. Less than surprisingly installing an after market fuel pump was a near ubiquitous modification made to the Ford's original, extremely spartan, engine design. The engine is in many ways a half-manufacture even by the standards of its day when it came to internal combustion engine thermal efficiency and refined running characteristics, which are necessary to lengthen the unit's life span and also to make the most of resources used to manufacture the entire car. The Model T components were made to wide tolerances to accommodate manufacturing techniques of the day to produce