Hi Kenny:
___Yes, this one fuel saving technique is the holy grail of hyper milers as well as fuel economy hounds everywhere.
___Here is how it works … Let us imagine you approaching an overpass at 55 miles per hour. The overpass has the same elevation on both sides with maybe a 25’ rise at the crest. Instead of applying more accelerator to maintain 55 miles per hour up the incline, letting off the accelerator to maintain 55 on the decline, and reapplying accelerator at the finish of the overpass to achieve a steady 55 miles per hour again, you simply lock the accelerator in the exact place that it was driving into the overpass. What you will see is your FCD’s instantaneous fuel economy stay at ~ the same spot as it was while cruising on flat and steady ground. At the crest of the hill, you might be doing only 51 - 52 miles per hour. You must still maintain your accelerator at the exact same spot (lock it down) and let the car accelerate back to ~ 55 miles per hour. What you will find is that by the time you have finished the decline portion of the overpass; your car will be at the ~ same speed (55 miles per hour) as it was when you approached the overpass to begin with. It is a simple energy equation with a trade of kinetic (velocity) for potential (height) and that potential (height) is being converted back to kinetic (velocity). The sum should be ~ 0 without all the effects of an automobiles fuel economy being taken into account and you will see the payback in fuel economy hill after hill after hill.
___Remember the guy using cruise control? His cruise forced 3 separate changes to the accelerator angle to maintain 55 miles per hour and 2 of those changes were fuel economy killers. I said 3 changes but in actuality, there were possibly hundreds depending on the reset rate and proportional band of the cruise (how sensitive) the cruise is. The big ticket item here is that you didn’t lose any fuel economy while traversing the overpass whereas those on simple cruise control dumped a whole lot of fuel for just a few scant seconds gained over your DWL technique in the process. This technique works in all cars but is quite easy to see with a game gauge in front of you.
___There are variations as well given not all hills have the same start and finish elevation. Some hills are simply to high to allow the bleed off to continue (climbing a 200’ rise over 1/2 – 3/4 of a mile will yield you 0 miles per hour at the crest which is ridiculous in all actuality), traffic conditions don’t warrant a full blown DWL technique, or you are climbing a mountain. After all, you only have so much kinetic energy to play with … Each particular hill, overpass, underpass, mountain, etc. is different so you will have to let your FCD’s teach you what is best for each as you encounter them.
___Jason, you posted while I was typing this one up. Sorry for overriding your post.
___Good Luck
___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___
Waynegerdes@earthlink.net