[arcosine]

This is my take, Ive never played with cam timing.

Advancing the cam is good for putzing around at 1000 rpm in top gear. This gives the best gas mileage, since engine friction varies as the square of rpm. But if the engine is limited by pre-ignition, then the ignition timing would have to be retarded, thus reducing engine efficiency. At highway speeds, though, the engine is throttled back so advancing the cam has no benefit, if it gained torque, the engine would run with higher manifold vacuum. Advancing the cam with a 3.5:1 final drive would be good.

Retarding the cam reduces MEP at low RPM. If the engine is old and has hot deposited on the exhaust valve or it otherwise limited by preignition the ignition timing could be advanced or the static compression ratio increased. The extreme case would be the Akinsion cycle used in the Prius with 13:1 expansion ratio. Thus this engine would actually be more efficient than advancing the cam, even though the torque and HP is lower. Retarding the 1.2 4 cylinder engne to where its is expelling 20% of the charge back out the intake with 11:1 static expansion ratio would be more efficient than the 3 cylinder engine with cam advance.