The 1.6 and 1.8 Vauxhall 8v engines circa the 80's and early 90's.
Bottom ends were nigh on indestructible and they were non interference so you could just drive it till the belt snapped.
The 1.6 would do 40mpg easily in the Cavalier of the day with the 1.8 not far behind.
Pity Vauxhall engines since then haven't been as reliable or economical.
Close second is the Rover V8, an all alloy Buick lump that was unpopular in the US so the rights were bought.
3.5, 3.9 and 4.0 versions were also made.
Has been in almost everything from vans to sportcars to GT 40 kitcars.