(2.500cc normally aspirated or 750cc compressed)
The golden age of the World Championship, in which Argentinian Juan Manuel Fangio created his legend, was quite simple in terms of Formula One engine rules. Ever since compressed units were allowed (with no more than 750cc), but no manufacturer tried to do something alike, so what prevailed were normally-aspirated engines up to 2.500cc. Mercedes, Ferrari, Maserati and Gordini were the main contenders on the first years, later joined by Climax, Vanwall and BRM.
And as we are talking about front-engined cars, architecture was not so fundamental as it would turn out to be some years after. Inline fours, sixs and eights; V8s and V12s were on the menu, with similar performances. Mercedes used to have the more powerful units, but not necessarily dominated, as Fangio would show, winning also with Ferrari and Maserati power.
On the end of the decade, finally the British power plants reached the stardom and broke the Italian/German dominance. Jack Brabham made good use of the Climax inline four on his Cooper to win the championship two years in a row. Power, at the time, barely touched 300hp.