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Old 05-30-2007, 07:53 PM   #1
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WW2 fuel conservation and wacky ideas

Back when the Allies were first experimenting with getting fighter escorts to achieve the range needed to accompany the bombers to Germany, the answer was to advance the throttle close to wide open to maximize manifold pressure
(including boost on supercharged engines), but set the prop governor to
lug the engine down to an absurdly low RPM to maintain a reasonable
cruising speed and thus maximize combustion efficiency.
The same can apply to auto engines.

Sometimes it does not work because the fuel map assumes you want max power and the fuel curve is a little on the rich side even on new cars.

Even the fe test on this site indicates that running the engine at wide open throttle and then coasting back down then speeding up again offers better FE.

What is wanted is the maximum possible cylinder pressure that is possible with the least ignition lead and leanest mixture. If the event happens at a low low rpm chances are you will not need much advance.
(because you will have time to burn without starting the fire while the piston is still coming up)

Then adjust the gearing so you maintain cruise speed at close to wide open throttle.


If I was a car company. then
I imagine an engine operating at wide open throttle with the drive by wire accelerator pedal actually controlling the torque multiplication of the CVT to adjust available torque at the drive wheels.

Imagine the cylinder pressure being constant and only the number of pulses per unit time changing.

That would yield much better mileage than the throttle back method we use now. I really think that most cars could get 40% to 100% better mileage
With this concept.
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Old 05-30-2007, 08:30 PM   #2
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That is a very interesting concept. I would need a MUCH higher final gear to even try it though. Is this essentially what we are achieving by short shifting into a higher gear whenever possible?

What keeps the car from accelerating when you have it at WOT? Would there need to be, say on a carb engine, a seperate control for how much fuel made it into the cylinder's? That way once you were at cruising speed you would adjust the fuel instead of the air to control your speed?

I guess that would cause the lean condition, at which point we have to worry about blowing holes in the pistons?
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Old 05-30-2007, 08:46 PM   #3
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The only problem with a CVT is that efficiency sucks compared to a standard, or even auto with tcc locked up, and in order to have "acceptable" acceleration, the lower limits of the CVT have to be relatively high. Which isn't the best for fuel efficiency. The Prius is a good example imo, since cruising at 55mph, BSFC is roughly 50% worse than it could be iirc, which is why people go on about the glide window and whatnot in order to get the best mileage. Imo, a standard trans with a near optimal OD gear designed for a specific speed range is the best for the driver that knows what they want. In order to accelerate, all they need to do is downshift. As long as the next gear can still wind out to ~100mph, it wouldn't influence normal driving one bit.
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 05-30-2007, 09:15 PM   #4
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BMW had some throttleless gas engines a while back IIRC, Valvetronic, they did not get 100% better FE though.
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Old 05-30-2007, 09:17 PM   #5
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Yeah, they just had enough control of cam phasing to the point where they didn't need a throttle. Still had pumping losses at lower loads.
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Old 05-31-2007, 07:37 AM   #6
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Yanno, ultra-tall gearing wouldn't be that hard for auto companies. What's needed is a two speed axle, one with 4.11 and 3.08, say. This would be better than an overdrive. They make two speed axles for trucks.
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Old 05-31-2007, 08:49 AM   #7
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What has just been described is a diesel engine. A diesel is at WOT at all times, engine speed is controlled by fuel delivery. If you want to go faster you add more fuel to the mix.

On the 2 speed rear axles, they put those into cars in the 50s. My dad had a buddy that had one that would race for money, he'd set in in low for a streetlight race, and high for a rolling start race. Bad thing about it was, you had to be stopped to make the switch.

A better way to go is more transmission gears, than a second shifting mechanism. The GM 4-speed manual has a 3.01 first gear with a .7 overdrive, I think the new 6 speed has a 6.X first gear and a second overdrive at 0.5 (not sure on exact numbers). This lets you run 3.23 rear gear, accelerate as though you have 4.10s, and cruise as though you had 3.08s.
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