While we're on the topic of driving in a SHTF scenario, most people don't know that you can take an old truck with a gas engine and make it run off firewood:
They're called "gasifiers" and they can be used to power vehicles and also generators. FEMA has a gasifier write up for those interested:
This always really interested me, however given that one of the (partial)combustion products is super toxic CO, I've always been hesitant.
The other useful tidbit is that many engines can run off ethanol (drinking alcohol), so in a pinch you could distill your own fuel.
I know some cars say that you shouldn't use higher than E15 or E85 or whatever, so same thing with wood gas, I wonder how it would work in a newer car with all the sensors. As far as your rudimentary carbureted, magneto driven, IC engine goes however, I can't imagine it not working as long as you get a decent mixture in there and a spark. You'd almost certainly (At least with Ethanol) suffer performace issues since the energy density is less, but in SHTF, going 60 vs going 6 is >>> Going 60 efficiently vs going 60 dirty