Here's another engine no list of workhorses could omit: the Ford Model T. Ford put this indestructible little flathead in 15 million cars from 1908 to 1927, then put a revised, larger-displacement version in millions more Model As and Bs for more than a decade beyond that (and let's not forget the amazing Model T-powered bootlegger submarine). Thanks to Pete for reminding us to include this super-workhorse. [Wikipedia]
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