It wasn't that porsche or toyota couldn't.....they didn't....... because they were not interested. The numbers were not there so they didn't bother. I've driven toyota trucks and cars for twenty years including lexus. Excellent vechicles, well thought out, drive and function beautifully. Very few problems, will run on and on.
No, I was there when the Toyota project was going on, I talked to them a lot. They were really trying. They had a Revlon Red Aztec with their engine on one side, the IO-540 on the other side. They could never make the fuel specifics the Lycoming did. You just can't beat the efficiency of a large diameter piston operating near detonation.
The Porsche Mooney was delivered to customers with the Porsche engine, there were a couple other planes the PFM (Porsche Flug Motor) and the PFM was not Porsche's first foray into aviation engines as they had also built a small motor that was around 65hp IIRC. Reportedly Porsche had over $75MM in the PFM program and walked away from it.
Just like every plane is compromise in features to optimize for a function, same holds true for engines. Driving constant speed/load propellers requires different dimensions to optimize that constant acceleration/deceleration diving wheels. If you want to maximize your burn below 3400rpm, you really want to have a 5" or bigger diameter piston to take advantage of the burn time. Personally I still prefer the big pistons with a gear and let them turn up to 3400rpm. The GTSIO-520 is actually very well optimized for driving an aircraft. The lower speed engines are handicapped below 2700rpm against detonation at over .5hp/CI. It can be managed, but you have to use some caution.
Thing is there is no new engine science between a 1930s engine and now. The physics of the fuel haven't changed. There have been some metallurgy improvements, and those have found their way to the aircraft industry as well.
We gain efficiency and precision with EFI, but in a mostly steady state environment, that is not that difficult to achieve with current mixture control. It would be nice if they gave me a 4° advance setting I could use when in a low load leaned out cruise, but that's really all the variability I need for efficiency.
Where these systems pay off is in reliability and durability across the industry. With EFI, you know the mixture has always been correct, and if someone was operating for all it's worth, the engine management system can detect and prevent detonation. Engines are always their most efficient at the edge of destruction. It is an edge as well, fine on one side of the cliff, peddling to your death like Wiley Coyote on the other. This is where the electronic management systems gain their great advantage, especially in cars where you are constantly changing load. It can real time manage the engine at the edge for maximum performance and efficiency.
I have nothing against these systems at all, the reliability of the electronic systems now exceeds the reliability of the mechanical. Neither however are failure proof. I don't really see a great efficiency advantage available to a knowledgeable engine operator. I don't think I would have seen a significant difference in my 310.
. Same could be said about buying a Buick. Just because you haven't owned any modern American vehicles isn't as much a statement about their quality as it says about your willingness to give them a chance. Trucks are a bit of a different story, but my 3 Ford F-150's ('90, '98, '08) have been virtually flawless and required nothing but routine maintenance.