Thirty years ago my hobby was tuning the lightweight Coventry Climax derived engine fitted to the Singer Chamois. By fitting long inlet tracts in the induction, huge valves, a full race cam shaft and sports exhaust it was possible to make this engine produce enormous power with great efficiency an high revs. 100mph in top gear at 7,000 rpm was its natural gait. It could cruise all day on part throttle at this speed. It was, however not optimised for driving at lower revs. If you were not in a hurry then the shortcomings of an engine with had such a narrow power band became obvious.
A little car like this could be tuned to cruise at 100mph
The amazing thing about this car was the low fuel consumption at these speeds. A by-product of high efficiency is low heat wastage. Consequently the engine ran cool at speed and was largely reliable, I use the term ‘largely’ advisedly here. Sub systems were not designed for such speeds and I had to put on a large alloy driven pulley to slow down the cooling fan, water pump and dynamo.
My point? engines can be hugely efficient if they are not compromised by the tedious design limitations of performing adequately at various loadings and speeds. The obvious solution – a pure hybrid with only electric motors driving the wheels and a small diesel generator acting as a range extender.