"older ICE powered prop planes" in this context means any prop plane, and about 95% of those used for GA. Brand new ones require leaded gasoline as well because with the exception of fuel injection the engine designs are basically identical to those 50s and 60s era planes.

Being pedantic, but turbo-prop planes use a jet engine to turn the propeller, and so use jet fuel.

That's going to be bigger twins and prop planes like the Pilatus

Being more pedantic, turboprops use gas turbine engines to power the propeller. "Jet engine" is incorrect when referring to gas turbine engine other than turbojets, such as turboprops, turbofans and turboshafts. Turbojets were the first variant of gas turbine engine to be put into use so "jet engine" ended up being used as a common term. Modern "jet planes" often use turbofans for their greater efficiency at similar performance levels, but "fan plane" sounds silly. The M1 Abrams uses a turboshaft engine but I've never heard it called a "jet tank" (which sounds badass).

I appreciate the double pedantry.

I should've known intuitively that a turboprop isn't a jet engine because the thrust comes from the prop not the exhaust.

Unrelated pedantry - even still, significant thrust does come from the jet engine. 5-10% typically.

They don't require leaded gasoline, they require 100-octane gasoline. It's just that until recently, a certified, unleaded 100-octane avgas did not exist.

it's not actually primarily a lubricant, it's an octane-increaser (detonation reducer)

IIUC, it's both, but you're right lubrication is not it's primary purpose, but I think the reason leaded fuel is hard to replace is that the lubricating properties are difficult to replicate.

> wherein it served as an effective antiknock agent and reduced exhaust valve and valve seat wear.

https://en.m.wikipedia.org/wiki/Tetraethyllead

That's mostly an issue on cheap engines without hardened valve seats. Aviation engines switched to hardened valve seats well before WWII.