I just found something that shows that Cam Dynamics experimented with valve timing and found that retarding the camshaft improved fuel economy. They apparently were thinking about selling something called the "camshaft retarder". My guess is that it would retard the camshaft during light load operation. Check this link:
Energy Citations Database (ECD) - - Document #5538464
This is the important part from that page:
Recognizing that camshaft design in the modern automotive engine is at best a compromise for overall performance, Mark Heffington of Cam Dynamics, Inc. set out to maximize gas economy through the utilization of variable cam timing.^The initial question was whether gasoline economy could be improved upon through varying the value timing over the operational range of an automotive engine.^The testing procedure duplicated the load conditions that the automobile would be experiencing during operation.^We tested gasoline consumption from IDLE up through 60 mph in 10 mph increments.^Without question, variable valve timing is a realistic means for improving fuel economy in today`s automobile.^Further testing and development need to be done to work with the pollution controls which have an effect on the results.^The camshaft retarder is an excellent device to alter the valve timing of the standard camshaft in order to achieve better fuel economy.