Mcdowell's Sterling engine is claimed to be, at peak, 50% efficient. That's considerably better than the current Prius, which reaches 40%, and Toyota's next gen hybrids which reach 41% thermal efficiency coupled with higher output.
FYI, VW's diesels are nearly 43% efficient.
But that won't get a normal sized car to 100MPG. Consider the diesel, at 43%, achieved just over 40MPG on more energy dense diesel fuel. The current 40% efficient Prius with hybrid drive reaches 55MPG in real world use. A 20% improvement would mean MPG's in the 60's.
FYI, VW's diesels are nearly 43% efficient.
But that won't get a normal sized car to 100MPG. Consider the diesel, at 43%, achieved just over 40MPG on more energy dense diesel fuel. The current 40% efficient Prius with hybrid drive reaches 55MPG in real world use. A 20% improvement would mean MPG's in the 60's.