14.7 lbs of air to fuel is what is attempted to be achieved. In reality it is usually less. 

With a normally aspirated engine a vacuum gauge is the easiest way to get better MPG. Training your foot to try to get the highest vacuum readings at all times will get you the best MPG.

In a force fed engine with OBDII the calculated load reading basically gives the same result but is inverse. The lower the calculated load number the better the fuel mileage. With OBDII this also applies to normally aspirated engines.

It has been demonstrated that in some cars with certain normally aspirated engines, with overdrive top gears when driven at certain highway speeds better MPG is achieved driving in the one to one gear versus the overdrive. At much higher than speed limit speeds the overdrive gear then gives better MPG. This usually the case in smaller engines with four valves per cylinder that make their power at higher RPM's. I used to have a 16V 1.8L Jetta that this was the case.

In most cases turbocharged engines get better MPG when driven in overdrive. They like being under mild boost and lower RPM's. Most cars that have turbo engines will have a numerically lower ring and pinion than the normally aspirated version.

So, in a Vanagon with a turbo gas engine a lot of experimentation with overdrive gear ratio's would have to be done to find the best MPG at the speed you like drive at on the highway. It more than likely is somewhere between what works for a TDI and what works for a normally aspirated engine.

John Wessels
Scuderia Black Forest

-----Original Message-----
From: David Beierl <dbeierl@ATTGLOBAL.NET>
To: vanagon <vanagon@GERRY.VANAGON.COM>
Sent: Sun, Mar 25, 2012 10:21 am
Subject: Re: Fuel consumption in different gears - how does the energy / fuel work?

At 08:26 AM 3/25/2012, Chris S. wrote:
>Look up stoichiometric fuel ratio, run it past your RPM
>observations, and you might get a part of your answer.

~14.7 pounds of air to one pound of gasoline, right?  

Yours,
David