Few questions for easy, $0.00 modifications

[theholycow]

You should have 100% traction/grip whether you're going up or downhill, under normal conditions. If you don't, you're either racing or you've got something very broken.

When you're going downhill, if you've got a modern engine and it's above 1000 rpm, it's using zero fuel. The only difference between coasting downhill in gear and coasting downhill in N with the engine shut off is that you'll gain a little more speed doing the latter, due to the road not having to turn the engine and operate the accesories. The energy used to recharge the battery after restarting is probably slightly less than the energy saved.

I disagree with your idea about aerodynamics. Your vehicle displaces exactly the same volume of air going up or down, has the same ground clearance and the same drag coefficient, and the same amount of pavement under it. Remember, the road's angle changes along with the vehicle's angle; so it's not like the vehicle pointed up will catch more air under and less air over or something like that.

Momentarily, when cresting the top of a hill or in the bottom of a valley, the vehicle's angle relative to the road changes, and at that point the balance of air going over vs. under changes momentarily; coming over the top, the bottom of the vehicle parachutes a bunch of extra air, while in the valley entering the uphill the ends of the vehicle are closer to the road and let less air under.

[Mr. Pig]

In my Cavalier, per my ScanGuageII, when coasting in drive at around 55mph I see around 55-60 mpg, if I pop it in neutral I see around 125-130 mpg. I'm having trouble understanding how the fuel cutoff could be using zero fuel. If there was no fuel at all, the engine would die and effectively have to be bump started to get going again, which isn't possible in an auto. Perhaps it is just cutting fuel to a point that it is running super lean? Or is my GM vehicle just not the norm?

[theholycow]

Originally Posted by Mr. Pig

In my Cavalier, per my ScanGuageII, when coasting in drive at around 55mph I see around 55-60 mpg, if I pop it in neutral I see around 125-130 mpg. I'm having trouble understanding how the fuel cutoff could be using zero fuel. If there was no fuel at all, the engine would die and effectively have to be bump started to get going again, which isn't possible in an auto. Perhaps it is just cutting fuel to a point that it is running super lean? Or is my GM vehicle just not the norm?

What was the tachometer reading?

If it's still in gear and the wheels are turning the halfshafts are turning the diff is turning the driveshaft is turning the transmission is turning the crankshaft, what's the problem with reducing the fuel until zero fuel is injected? As long as fuel is resumed before the RPM drops below idle speed, no restarting will be required.

A Cavalier isn't exactly the showcase of all the latest in modern technology; I suppose it's possible that it might not support DFCO, though I'd guess that it's more likely that it just wasn't revving high enough. 1000 rpm is the number everyone says for DFCO and it's definitely the borderline point for my VW, but I'm not sure that it's the same in all vehicles.

Pale: I hope your guess is wrong. I am planning to buy a SG and I'm counting on it being able to report actual fuel consumption volume. If it can't, I need to come up with some other gauge to do it.