Just thought I would add some info.

I am not a tuner by any means. I would say that lean burn would be okay on these engines. Guys with LS engines are doing it all the time. I know of a guy with a C6 Z06 and he pulls great numbers MPG wise with lean burn cruise. Also some civics had this feature. The USA EPA doesn't like lean burn. They see it as bad for the environment.

I'm not sure how you guys do tuning on the 928's but I would look into that and getting a switch that you could activate a lean burn image while on the highway. That way its not automatic. You could pick up quite a bit of MPG from it. LS1's do great with it or get a real overdrive to run like 1200 RPM at 60 MPH. My buddy a couple times got 27-28 MPG in his LT1 Firebird 6 speed. So its possible just need the gearing and tuning on your side.

An LT1 Firebird will get 28 mpg on the highway bone stock. The T56 6th gear ratio is 0.5:1

If I remember right Charles Lindbergh basically did the same thing during WWII with P-38s. He was an "advisor" and developed techniques that extended the range of the Lightnings. Basically he reduced the rpms and leaned out the mixture. I think he ended up getting about 10 to 20 percent better fuel economy. I think the mechanics where skeptical at first but it later was proven to not be detrimental.

Sorry to rain on your parade, but you will just have to get used to the idea that fuel has been to cheap for to long, and it is going to go up in price. And it is going to go up in percentages that you can not gain in economy from a 5 litre V8 hauling around a 928. So relegate the 928 to a sunday driver and get into an economical buzz box for the week. I'm afraid Americans will one day soon have to realise that you have a failed and unsustainable economy, and look outside your own borders to see how the rest of the world is coping.

One barrel of oil contains the amount of energy the average male puts out in a lifetime. Imagine an average car uses 10 litres per 100km, and fuel costs $1.50 per litre. Ok now if I were to ask you to physically carry me 100 km and I will pay you $15 dollars ! fuel seems very cheap then, doesn't it !

Cheers Roy

It's not our economy that's unsustainable, it's our government's lack of leadership, and vision.

That's not something you have a monopoly on, unfortunately

That aside, lightening your right foot will make more difference than lean burn at cruise.
Driving habits make all the difference, and the tall diff ratios on 928s already allow decent cruising speed economy.

Fuel is much cheaper for youall in the U.S.
We got ponds of it over here and we pay more-(!!!!)
But honestly N.Americans are spoild whiners-I am guilty as well and I am deep in the oilfield.
What do you and we all propose when oil can NO longer be purchased with U.S bucks?

Most 928-ers could possibly be reduced to Sunday drivers.
I don't think you can even purchase insurance for-just- those days.
Double whammy!
Dammit.