[Blood of Tyrants]

There is always a market for more effecient engines. More efficient means more power out of a smaller package. Smaller means less weight. Less weight means even more fuel savings.

You forget the necessary heat loss. Develope a lubricant that will withstand 400 deg F and you can greatly increase efficiency.

Have you considered variable valve timing and radical cam design in conjunction with high compression?

[John Jamieson]

Yes, raising engine temperature helps too, Smoky melted several Buick v6's testing the idea in the 60s. He made some of them into V2s!

[nightdriver]

"More efficient means more power out of a smaller package."

Actually, just the opposite is the way it works. A highly efficient engine of any process tends to be very large for its power output.

The diesel engine outshines the gasoline (spark-ignited) engine every time in efficiency because of its higher compression ratio. However, it will weigh over twice as much as an equally powered SI engine.