"Green" ACVW performance engine?

[Wally]

In what country do you live?

In mine we can get propan (LPG, liquid petroleum gasoline), which is very clean burning and has an octane rating of well over 100
It also costs less than half the cost of petrol/gas, so you get the best of both worlds.
My 1,8 type 4 runs/ran very well on it.

But availability of alternative fuels is the first to consider...
The aircooled engines usually don't differ much from modern liqued cooled ones regarding the fuel used.

Regards,
Walter