In my gearhead days I had a dead-tree copy of Yunick's Power Secrets, and read about his adiabatic modified car engine.
My understanding at the time was that the main barrier to market was emissions related. Oxides of nitrogen in particular were far too high from the high temperatures. If you look at an emissions test summary NOx is one of the few things they actually measure.
> NOx gases are usually produced from the reaction between nitrogen and oxygen during combustion of fuels, such as hydrocarbons, in air; especially at high temperatures, such as in car engines. [0]
So I'm pretty sure the opening line "meets all emission standards without electronic equipment" from TFA is incorrect. Or maybe was only briefly correct in 1983...