I put Koenigsegg’s freevalve tech on a Miata... It runs and drives!

Agreed, but there's also Koenigsegg, which has managed to eliminate the need for cams, and complete heads from ICEs, replacing them with their 'freevalve' tech (which basically replaces the timing chain with computers so that instead of having one or two modes that a camshaft can opt into, you can precisely dial in bespoke timings for every RPM, or every RPM and speed, or ever RPM / speed / gear combination. They've also practically reinvented the transmission to invent a new transmission that eliminates moving gearsets and gives you a dual-clutchish transmission with a 6 speed manual AND a 9 speed automatic in the same device. IIRC, the Freevalve tech is like a 30% efficiency hack for any ICE you put it on, and it's a part of how Koenigsegg are managing to squeeze 600 brake horsepower out of just a 2L, 3-cylinder engine. Wesley Kagan reimplemented their freevalve technology on his Mazda Miata, and it's probably the coolest hobby automotive project I've seen in years. [this video] Here's a really cool explainer on the transmission - [link]

There's some nuance here. If you care about fuel consumption or emissions, then EFI is the current best way to reduce both, and that requires "computers and software" to operate on the timescales required. I put scare quotes around those terms because you can do EFI on an Arduino, which is at least an order of magnitude more powerful than what automakers shipped in the 80s. In any case, EFI gives you more control over the engine and vastly simplifies the overall product. I don't know if you've seen the mechanical fuel-injection pumps used by tractor diesels; they are basically tiny engines unto themselves, with their own little block and camshaft [0]. There is an entire world of diesel performance modding with a subset of it dedicated to modifying the Bosh P1700 mechanical fuel-injection pump to change timings, handle higher RPMs, and run higher pressures. I would not call it, or its carburetor cousin in the gasoline world, "simple" compared to computer-controlled fuel delivery. An open-source ECU project, on the other hand, enabled a hacker to implement Koenigsegg's Freevalve tech on a Miata [1]. [0]: [link] [1]: [this video]