If the grade is fairly steep and sustained I woud actually reach my highest pulse speed at the bottom then gradually lift the pedal as I try to maintain the same speed regardless of the fact I am going uphill or downhill. Constant speed will give you the lowest overall drag, by avoiding the higher speeds exponential increase. Vertical climb no more than 60 feet in this example.
That's my experience, we have few shallow grades here, I have over 70 feet of vertical climb on two hills just to get out of my small subdivision. About 230 feet vertical climb to get to the closest shopping.. 2.6 miles away.
With a racecar on a 16' tandem axle trailer behind an Expedition @ 8800 lbs total weight I can get 17 mpg at 60 mph average speed using this technique.. Do most of the accelerating at the bottom of the valley, gradually slow going uphill and coast downhill.
Put the cruise control on and go the same average speed and it's more like 14 mpg.
In scenario #1 we average (17+38)/2 or 27.5 mpg at 60 mph.
In scenario #2 we average (26 + 35)/2 or 30.5 mpg at say 58 avg mph.
It's possible you did better simply (or at least partly) because you slowed down. Slowing down is pretty much a sure-fire way to enhance mpg. But eventually you reach a limit, with this tactic. The trick is to figure out how to operate more efficiently, which means enhancing mpg without sacrificing distance or average speed. Efficient operation generally means large throttle openings, which is inherently counterintuitive.
Test 2: decelerate up hills, accelerate down
Depending on the circumstances, this tends to happen naturally. But if you take this too far, you end up with a large variance between your min speed and your max speed. A moderate variance is OK, but when it's too large it tends to create various problems. The extra aero drag was mentioned. It's also more likely to annoy other drivers, and more likely to create a problem with speed limits.
Originally Posted by bkrell
the numbers were silly-like 9 uphill then 55 mpg or so downhill.
That's typical of what happens with an instrument that reports instantaneous mpg. There are wild swings. The implied strategy is obvious: never drive uphill, always drive downhill. Kind of like the classic stock market advice to buy low, sell high. Easier said than done.
The downhill didn't change much when I dropped the speed and got close to 26 mpg uphill.
From 9 to 26 is a big jump, and I can't explain that. But maybe it's real, so keep doing it and see what the results are when you fill.
The instantaneous information is helpful, but it becomes more valuable when you put it in the context of a broader interval, like a 'trip' (however you define that).
Does the fact that I have a turbo car make a difference?
Dont let the turbo bother you too much, it just makes it possible to extract more power from less engine.
A big plus is the boost guage which is basically a vacuum guage, with ability to show pressure, in positive or negative values.
This allows a greater sustained load on a smaller engine which should be more efficient.
The negative is it can also consume a lot of fuel quickly.
The best example I can think of was the 1.5 liter Alfa grand prix engine of 1950. 90 cubic inches 2 stage supercharging and 390 horsepower, at 2 MPG!.
Your turbo should only be used to sustain steep grades (or emergencies) if mileage is your priority. Other than that use the boost guage to try to maintain the lowest manifold pressure (close to 0) when you are pulsing in the highest gear you can use for your pulse. Gradually depress the gas pedal until you just reach 0 on your boost guage, then you will get a feel for your best pulse acceleration.
If you have to choose a lower gear or some boost use the boost. This would be up significant grades like those the big rigs can not maintain higher speeds.
For hypermiling avoid the turbo.
Use engine braking instead of friction braking because it shuts off all the fuel to your engine when the engine braking keeps the engine above about 1000 rpm. The savings can be significant if you can eliminate as much idling as practical without making everyone around you mad.
But see, that's the other thing I don't understand. Are you saying on acceleration? That's usually my guide. I avoid boost if at all possible, which I can usually do very well. But are you saying that if I have a choice of accelerating with high vac verses close to none, I would get better FE? I somewhat understand pumping losses but on bal;ance, I seem to still be doing better at full vac.... Maybe it's just b/c keeping high vac gives me room to exceed my target and still stay on the negative side verses when I try to maintain no pressure I'm dipping into boost???
fumesucker, to be honest, that's another thing I don't understand, closed/open loop? Can someone clear that up for me??? But otherwise, see what I said in my previous response, econ just seems to dip for me when I go into boost....