ASK KEVIN: Why Doesn’t Anybody Produce a Square Four Engine?

A query from a man who greatly admires the Ariel Square Four.

ariel square four illustration

QUESTION: I have admired the Ariel Square Four engine for a long time. Has a manufacturer produced a Square Four since? If not, why?

Bob Kelly

Denver, Colorado

ANSWER: They certainly are attractive from the standpoint of balance. Liquid-cooled 500cc Grand Prix two-strokes have been built this way, but four-stroke square-fours would now have to be liquid-cooled as well because the front cylinders block cooling air to the rears. Also, there's some problem with packaging. The original Edward Turner Ariel did not have a very free-flowing intake arrangement.

Honda's V-4 RC30 barely had room in that wide vee for its four carburetors. Point the front intakes forward and the rears rearward? Updraft exhausts in the middle? Or vice versa? The 500cc two-strokes had their exhaust ports face two forward, two rearward, with disc-valve intakes pointing right and left. Or, with reed valves, the cylinders were opened into a vee to allow forward-facing reeds and carbs.

It's fun to play with ideas like this in one's mind. Thanks for taking the time to write.

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ariel square four diagram