[oldtamiyaphile]

My Flathead (sidevalve) Ford gets 14mpg. There's 4MPG by my reckoning just switching to 12V and going from generator to alternator. A more reliable starting system would mean I could turn it off in traffic so not be idling. I know MPGuino reports that not idling saved me 10% on my old petrol van.

Add alloy heads, modern EFI, more modern gearing and you'd be knocking on the door of what a modern petrol Hilux gets.

But as said above, it's just so much easier to buy an off the shelf modern engine. A Ford Ecoboost 1.0 produces the same power and torque as that 4.2 V8, but with the added benefit of being 100kg lighter, which means you can have a lighter gearbox, smaller brakes, etc.

It might make a bit more sense to update a lateish model engine. The 1.5 SOHC in my 2010 Proton dates back to 1991 or so. It would be a simpler task of adding those multi hole injectors, replacing the cast exhaust, maybe doing some more technical bits like machining lighter valve train parts. This engine doesn't even have EGR!

At the end of the day, even today's production engines are built to a price and therefore there's always room for improvement. Replacing steel with alu, or ti is always an option.