Hills vs. gently rolling hills.
 

Flat ground doesn't really exist, so I won't comment on this. But I have observed that, it seems, significant hills are required to achieve long enough coasts to really bump your mpg up over what you could otherwise do while DWL on gently rolling hills. Does this make sence?
I've recorded 54 mpg in mountains of western PA, but only 51mpg in the rolling hills of the the Carolinas coasts. Are these two mpg numbers too close to declare a clear winner for better terrain? What have you observed?

I think the difference depends mainly on your aero and rolling resistance. The less resistance you have one the car, the more you can take advantage of hills with less inclination. I've noticed this especially with my recent wheel swap.

Part of the issue I think with slight downgrades that you can't EOC on is that even if it would only take 1hp to maintain speed the car needs to put out like 4 or 5 hp just to overcome all the losses in the engine and transmission, which lowers potential mileage around those sorts of hills.

I would think that slightly rolling would be better. Be able to keep it in high gear. Long downhills are nice, but I don't gain what I would lose climbing the steep hill.

Others may have different results.

No, I think you have it. My nightly climb is to 4,675 feet over 14.7 miles. I never get it all back on the downhill, as my best tank (climbing the mountain only once) in the Saturn was 1.29 mpg higher than my best effort tank with the nightly climb.

I drove 7238 miles last month on a cross-country trip in my Scion, and got my best mileage in the mountain west (going both directions)

My worst mileage was in the flat lowlands of the southeast, from Texas through Louisiana, Mississippi, Alabama, Georgia, and Florida. I attribute that to E10 fuel, having to run the AC, and using cruise control a couple of days.

All-in-all, I averaged 44.7 mpg over 35 days. My best day I got 59 mpg in the morning driving 165 miles from Gallup NM to Tuba City AZ, and 50+ mpg in the afternoon continuing on to St. George UT - a total of 54+ mpg avg over 370 miles. I averaged 51.5 mpg for the last 1213 miles from Gallup back to the Bay Area. The best roads were long downhills. Even if I couldn't keep my speed up coasting down them, I was able to gain mileage on every downhill pulse and glide cycle - more than I lost climbing the uphills in the first place. On one memorable downhill from Donner Summit to Reno, I averaged 75 mpg for 40 miles.

When I recorded the 54 mpg tank, it was without the SG. On this most recent venture I had the scan gauge and noted that I easily got up to 53.5 mpg in the hills of south east PA/DE/MD, however when I hit the gently rolling hills of Virginia and the Carolina's, I struggled to get 50 mpg. I'm driving an automatic, so no EOC, but I do coast in gear as much as possible and thats where this observation comes in. It was quite frustrating watching my mpg tick down from 53.5 to 51 as I would climb those gently rolling hills only to find I could not coast enough distance to make up the loss. The best technique I could come up with was to minimize the loss going up, going as slow as 45mpg so I wouldn't take a big hit, then gas it a bit to get up past 50mph then just feather the throttle for as long as possible, but it still took what seemed like 30 times the distance of the climb to gain back the loss and if there were several hills back to back, it was just a loss. I'm looking for advice on tackling this type of terian and to see if others have noticed this????

A guy in the hills with an Escort claimed over 100 mpg (or was it 400?). Must have been the hills.

Are you speaking of COZX2 from Gasavers?

Yup

Yea, I pretty much read everything he wrote on there. Being at 10,000 feet and driving in those hills along with his technical expertise and persistance to learn how to pulse and glide optimally got him the 100+ mpg numbers. I have copied many of his mods :)

SVOBoy, how much do those insight wheels wiegh?

Tygen - I believe that the gently rolling hills are perfect, even for neutral coasting w/ the engine on, because you can maximize your downhill stints with only short bursts of acceleration, and even the curves slow you down a bit if you pick up too much speed.

The longer, steeper hills aren't great, because you're wasting alot of energy in braking trying to keep your speed down.

I try to time my acceleration so that I can put it in neutral and speed up to the speed limit going down a hill, so that I don't have to waste as much gas speeding up.

+1 for rolling hills. I have a couple good ones on my commute and coasting in N with my auto Neon helps the mileage quite a bit. I'm not afraid to speed on them either but usually I don't go more than 25km/h over. The key to hills I think is climbling them, for my cars it seems top gear is always best so even though it seems unnatural to get a run at a hill, if it helps you stay in top gear to the top I think you come out ahead.

I have only had experience with the rolling hills of central NC so can not say about larger mountains.

It was challenging at first because the distance between hills varies and the EOC is usually much shorter than you would like. Meaning you could coast for a much longer distance than the hills allow. I learned to just go with the flow. Say I pulse to 50 mph in a 45 psl zone and EOC on top of a small hill. I coast for… maybe ¼ mile and get down to 40 mph. My choices are to pop the clutch and accelerate to 50 mph to begin the next hill climb or coast another hundred yards right to the bottom of the hill before popping the clutch going 35 mph. (These are fictitious numbers, for example only). Which one works better for total trip mpg? It really depends on the hill you are about to climb and the next EOC coast on the other side. If it is a sloooow gradual climb then I gain some momentum to DWL the hill. If it is a shorter climb I coast right up to it then accelerate more aggressively for a few second before DWL up it.

The technique that works best in all circumstances is only possible with no traffic behind you. That is to start at the psl and coast whatever the distance available is. Then DWL the hill according to your end of coast speed and EOC the next downhill at whatever speed you are at. I’ve had a few days where I tried this on my commute and the results were fantastic! I had a few EOC starts going 25 mph and coasting down to 10 mph. I also had EOC starts going 40 mph and ending at 36 mph. What screws the whole process up is that vehicle appearing in your rear view mirror and you have to accelerate to the psl before they get to you. Unfortunately this happens when you are going 15 mph right at the bottom of a steep hill!!!

Bottom line I have come to think that small rolling hills will return better mileage than large mountains like Brian climbs. There is just no way to get back most of what you put into the climb. Small hills you lose much less climbing so do not need to gain that much more coasting.

I think hill mileage results depend largely on having a long uninterrupted runout. I got 59 mpg on my Scion (210% of EPA) over 165 miles in the mesa country on the Navajo Reservation. The long runouts going down the mesas gave me great mileage, and there was no traffic to contend with. Most of the time going down steep mountains, I end up stuck behind some slug who makes me bleed off all my momentum with my brakes. Steep long hills do allow me to get great mileage, as I DWL up them, and get my best mileage P&Ging massive miles on the way down. EOC just comes out even, with a slight loss, but P&G drags out the coasting miles and allows big mpg numbers.

I think you hit the nail right on what I saw. The amount of effort and gas spent going up the hill can not be regained on the coast down because you can't stay at a speed high enough to please the dude stuck behind you. At least the larger hills of western PA alowed for nice long coasts above the speed limit after climbing the hill. There were a couple times I let the coast run out to 35mph and that seemed about right to regain what I lost going up, but that is just not doable on I-95.
Also, it's difficult to quantify "Gently rolling" hills. To someone in Colorado it's different that someone in Kansas....More of an opinion thing....