VW's 2.3L ovaL-piston dieseL I just came across this on Ti Kan's Audi site... in 1990, VW developed a 2.3-liter 4-cylinder diesel engine with oval pistons (well, actually they're elliptical, not oval):

http://www.ibiblio.org/tkan/audi/audi-misc/oval1.jpg

Comparison to a standard 1.6L diesel block:
http://www.ibiblio.org/tkan/audi/audi-misc/oval2.jpg

The bore was 99.49 mm in the long direction, and 76.5 mm (same as the 1.6L dieseL) in the short direction. The crank was the same as the 1.9L diesel. The exact displacement was 2343 cc, with 57 kw (76 HP) and 165 Nm (122 lb-ft) torque. No turbo. The pistons were developed by Mahle, and the engine was used in several VW test cars, but obviously never put into production. It was written about in 1990 in Germany's "Auto Motor und Sport" magazine, if anyone cares to look it up and translate.