terrybarr wrote:Don't you mean somehow adding a bit to the cylinder head or shorter pistons?
Not to convert it into a diesel, no...
terrybarr wrote:Humour aside, I often wonder why engines that absolutely must have 100LL are still being installed in brand new aircraft. I can't see leaded fuel still being available in two or three decades time.
They're not, really. They're being produced for the octane rating available in fuel these days. Most aero engines have long since had hardened valve seats, so the lead is irrelevant. It's just an octane booster. As soon as someone comes up with a 100UL which is universally accepted as a 100LL replacement, it'll be able to be used in pretty much all existing aeroplanes. No one's going to design an engine for mogas, and in most of GA-land, they don't know of the existence of UL91. So rather than invent a new avgas, they make engines which are able to use what's available. Which is 100LL, 80/87 having long since been forgotten.
If you wanted to use lower octane fuel and maintain the same power, you'd have to either increase the engine capacity or increase the RPM. You could have a complete redesign of engine with a greater number of smaller cylinders which would allow high compressions with low octane fuel, but that's a big risk in engine design. Many have tried, many have fallen by the wayside. Rotax is one of the few who have succeeded in a small cylinder high RPM engine being acceptable to the masses but they are only for low-ish power engines at the moment.