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The PoD for this is probably sometime in the 1960s, as pushrod engines and superchargers used to be more common on automobiles than overhead cam engines and turbochargers. Now pushrod engines have mostly been relegated to the North American market and niche racing applications, with superchargers having a very small niche for luxury and racing applications.

Despite being considered somewhat antiquated, pushrod engines do have some advantages relative to overhead cam designs, such as being significantly more compact and lighter for a given displacement. This gives them high power density, and for companies looking to save money it allows iron to be used for the block and heads instead of more expensive and complicated aluminum techniques. Traditionally pushrods have also been more reliable than overhead cam engines as they are less complicated and tend to suffer less damage when they do fail. However, pushrod engines have the disadvantage of putting out less power for a given displacement, and they have difficulty using multiple valves, variable valve timing, and variable valve lift. European and Japanese companies may have been encouraged to move towards overhead cam technology due to displacement limits and taxes, as well as the higher efficiencies possible.

The same technical, economic, and legal reasons that led European and Japanese firms to pursue widespread use of overhead cam technology may have also led them to pursue widespread use of turbochargers in order to increase power output at a given displacement. Like pushrod engines, superchargers were once in widespread use, being used on pre-World War II luxury automobiles, high performance piston aircraft, and muscle cars of the 1960s. It's somewhat less clear why turbochargers have become so common, even for lower market vehicles. Superchargers proportionately increase power with engine speed, so they give a smooth and continuous power boost, while turbochargers lead to reduced power outside of their optimum operating range, can be slow to respond (turbo lag), and can kick in quite suddenly. While the disadvantages of turbochargers have been reduced over the years, and they are less expensive than superchargers and more fuel efficient (although superchargers increase fuel efficiency at a given output as well), it doesn't quite explain why the technology is very rarely seen now.

I'm wondering if it might have been possible for pushrods and superchargers to have remained in more widespread use worldwide. Also, could supercharged pushrod engines have become popular instead of turbocharged overhead came designs?
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