OK, so we're driving local roads, say, ~30mph and approaching a stop. At what load/rpm/speed is it more efficient to just drive in VCM, then brake 'normally' as opposed to shifting to neutral early and coasting?

I've been trying to determine this, but keep getting inconsistent results...does anyone have some reasonably coherent results? Ideally we would be able to find consumption curves and determine the crossover, but...

While driving a stretch where you know you'll need to stop (or are downhill), the 'traditional' wisdom is to go into neutral and coast. I am assuming no forced auto-stop here...it's not always a practical/safe choice, depending on conditions.

BUT... we in the HAH have a new twist with VCM. There may be a crossover point where it is more efficient to keep 3 cylinders firing (in gear) for the duration, foot on gas for a while longer, than to go into neutral (all 6 firing). The trick is finding if and where that point lies and is it a reasonable state to be in.

Neutral is the lowest resistance and lowest fuel delivery rate, BUT all 6 cylinders are firing at ~600rpm.

In-gear with VCM on implies a higher fuel delivery rate per cycle and is always >idle rpm, BUT only has 3 cylinders firing.

Two different operating regimes mean two different consumption curves, which very likely intersect somewhere, though not necessarily.

Has anyone played with this and found a speed or condition where you MPG is better in-gear than in neutral? It may not exist at all, but I suspect it does. Not having navi in my car, I can't get instant feedback, complicating life.

thanks

 

Wayne is probably going to be the definite answer here -- but I guess neutral is better. Pumping losses at very low speed is going to be substantial, even on *only* 3 cylinders.