[red-beard]

Originally Posted by john70t

My understanding is high compression engines run very hot and need to be built beefy.
They also create a lot of NOX.

Still waiting for Mazda to add the water injection of a https://en.wikipedia.org/wiki/Six-stroke_engine, the long-stroke reduction of https://en.wikipedia.org/wiki/Atkinson_cycle, and a variable combustion chamber of a https://en.wikipedia.org/wiki/Variable_compression_ratio.

Yes. High compression means a higher flame front temp, which means higher levels of NOx. Diesels deal with this by using DEF (Urea). You could more easily do this for gasoline engines, since they do not need a soot filter (DPF).