Come up with a new engine design that fixes these three problems and you’ll improve IC engine efficiency by 50 to 100%. Boosting IC engine efficiency by that much would get you pretty close to the maximum possible theoretical efficiency according to Carnot. You'd still have friction and thermal loss to consider...
Carnot efficiency goes up with extended power stroke ratio. (i've been calling it exhaust stroke) that's the point. we're looking for 50% not 100%.