[Daox]

Assuming all variables stayed the same (yes, I know thats impossible), can we say that if an engine has greater volumetric efficiency or torque that it is also more efficient? I would tend to think yes.

I'd really like to hear some theoretical conversation on that idea, but I'll also share my situation as an example. I bring this up as I will be working on getting my 1993 Tercel back on the road fairly soon. The engine is going to need work in to the not too distant future (217k and burns oil), and I'm thinking about updating to a newer engine (5E-FE or 1NZ-FE). The newer engines are the same displacement, but put out more torque and at lower rpm, and thus I would imagine they're more efficient. Obviously (if you know Toyota engines), the 1NZ-FE is quite a few years newer technology than the stock 3E-E and would be the optimal choice. That also means it will be the most work to put in too...