Rotaries have gotten better, but that's it. A piston engine is far superior. It has much more tuning available to it and makes more power and torque. Also they are more reliable and more durable,...
Here's a few million mile pickup truck diesel engines - - - 7.3L IDI International (Ford), 6.9L IDI International (Ford), 7.3L Powerstroke Turbo Diesel (Ford), and the 5.9L Cummins I-6 engine...
very very very efficient. get a Ferrari
Improved answer.
It depends largely in what way you mean efficient. An engine can be efficient in many different ways, but usually not all ways at the same...