Here is a brief history of some of the major engines used during the first 50 years of the 500.
This is the Cummings diesel 400 cu. in. engine, it is
NOT a major engine from Indy. They tried diesels twice in the 30's and twice in the 50's without much success. The diesel was tried because it could go 500 miles on a tank of diesel without refueling. However the car was so heavy that it wore out tires quickly and they had more pit stops to just change tires.
This is the 1920 Monroe-Frontenac engine. A 4 cylinder 16 valve double overhead cam design. The Meyer-Drake Offy running in 1966 has the same configuration.
The 1920 Duesenberg strait 8 engine. Duesenberg ran Indy all through the 20's with basically their production engine. If you bought a Duesenberg for the street you got this engine. Today it would be like buying a Toyota Corolla and getting their F1 engine in it. Ooh doggies!
The 1926-29 Duesenberg. Eight cylinders and 90 cu. in.
Their biggest competition was the Miller supercharged engine. 91 cu. in.
During the 30's Duesenberg fell out of favor and Miller really took over. Here is the 1932 Miller-Offenhauser. 220 cu. in.
Here is the basic Offenhauser block used up until 1966. Very simple but very rugged. Everybody thought they had a better idea on how to coax a few more horsepower out of it than anyone else.
Another version of the Miller engine used during the 30's. The differences where mainly caused by the Miller race cars being front wheel drive so the engines were in their cars backwards.
In the 50's Meyer-Drake took over building what had been the Offenhauser engine. This would be the engine of choice until 1966.
The other side of the Meyer-Drake.
This engine based on a stock Ford block was designed by Mike Costin and Keith Duckworth and opened the door to all sorts of engines. However the Cosworth engine has probably won more major races than any other engine.