I know in the last 30 years turbos and superchargers have made it easier to make power, but I always hear about huge 7 or 8 liter engines made in the 70s or earlier, that will make like 200 hp at best. How is it possible to get so little out of so much displacement?
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There are a few reasons, but it mainly comes down to increased efficiencies at mixing air and fuel.
Older engines had carburetors. These were mechanical devices that mixed air and fuel for the engine to burn. Carburetors were not nearly as efficient as fuel injection, which is the technology cars use today. Fuel injection gets a near-perfect air-to-fuel ratio delivered into the engine.
Older cars had pushrods for their air intake and air exhaust systems. Modern cars have overhead cams with Variable Valve Timing (VVT). The way old cars let air into their engines was completely static – now, cars can control how much air the send into the engine *and* change the amount of air sent into the engine at different engine speeds to create more efficient fuel burning.
Due to advances in manufacturing, engines now also have higher compression and can withstand higher speeds.
Finally, in regards to the 70s specifically, environmental legislation that came in at that time caused some American manufacturers to detune existing engines (made before the environmental regulations) and make them weak from the factory to meet emissions requirements, instead of designing new engines right away.
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