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Old 08-26-2007, 06:15 AM   #1
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driving technique confusion

There's some contradictory information that's got me a bit puzzled:

You should not accelerate quickly. You should not accelerate when going uphill. So goes the consensus. Well, one reason for slow acceleration is to get to high gear sooner. But in that case, you want to go through the lower gears rapidly, and that does mean faster acceleration. I mean, suppose on a 5 speed you shift up to 4th quickly, then stay in 4th for a long time because the car simply can't accelerate faster because you got to 4th so early. The question is, should you have accelerated more and longer in 3rd (and 1st and 2nd), so that your stay in 4th will be shorter and you get into 5th sooner?

Engines are most efficient when under maximum load, correct? The technique of Pulse and Glide uses that fact. And you'd rather pulse when going uphill, and glide on the downhills? That seems to go against the above technique of waiting for flats or downhills to do acceleration.

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Old 08-26-2007, 06:55 AM   #2
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Well, I think what you need to understand is that there is a balance. I can accelerate quickly in 2nd gear to 5000rpm, getting me to 50mph. Then I could put it into 5th, getting me to 2000rpm.
If the car can't accelerate at all, you're probably in 4th too early. I've found the best results to be from when I accelerate through all the gears, shifting around 2200-2300. I plan my acceleration around that, and give a decent amount of gas while accelerating.

My understanding is that ICE's are NOT most efficient under maximum load, but more like 50% load. SO I give about 1/2 throttle while accelerating.
Even if the engine is more efficient itself maybe while going uphill, that just means more of the energy you put in is being outputted as kinetic energy. But you're also using more fuel, so it really doesn't matter.

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Old 08-26-2007, 06:58 AM   #3
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Basically, I think the key is finding a balance, which will be unique with every type of car. My parent's both drive VW's with the same 2.0L engine, and this car has crappy low end torque. I would have to modify my shifting habits to get maximum FE in those cars.
I can't confirm everything I've said, as my car is too old for a scan gauge. But going tank by tank, I am getting 70% better FE than EPA estimates for in town, so I'm doing something right.
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Old 08-26-2007, 07:03 AM   #4
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No confusion.

Take my car. If I shift at 3k rpm by the time I hit 5th that would be 70 mph. Most of the time I flip through the gears at 1700 rpm to 2500 rpm.

Your shifting pattern and shift points are determined buy traffic and load conditions.

If I shift at 4500 to 4700 rpm. Im at the peak of the torque curve. But by the time I pull third Ive broken all most all the speed limits with exception to turnpike speeds. Ive gotten 7 mpg, had fun and am inviting the po po's to speak with me.

The trick is. Smooth launch then get into 2nd as fast as you can. 1st is to get the car rolling. In my Civic if I was on any sort of downhill grade I could launch in 2nd. My Mazda will not launch in 2nd not matter what. So I launch and then pull 2nd in a hurry. 3rd comes around 2k rpm. If load is light or Im on a slighr downhill I go straight to 5th. Also make your shifts quick. Not hard ,,, but quick. The Mazda excels in quick shifting. Not power shifting! No need to man handle the process.

As for hills. Load drive up holding a stead throttle position if at all possible and back off the throttle or fas the other side. Lets take my MZ3. The most eff. place for it would be where the torque curve and horsepower curves cross. Well that would be 4500 rpm or so. So at that point the engine is at its finest. But drinking fuel like I drink whiskey at times. Nothing eff. about it for a fe driver. P&G MPG comes from the glide. Not the pulse. Pulse to hard or in the wrong conditions and you will see-saw the mpg.

If you have a SG it becomes very clear. Very fast.
09 HCHII, w/Navi
07 Mazda3 S Touring, 5MT
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Old 08-26-2007, 07:16 AM   #5
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You can only accelerate so fast, simaler to if you are sky diving you don't reach maxum speed in that first instant, you could put on a jet pack and push your self down twards the ground faster, and that will take more energy.
It seems like it would be true that your engine runs most efficent under load, but most car engines are also designed to dump in more gas when they are under great load to give you extra power, because I don't have any kind of instant feedback in my car I can't truely say, but I would assume that accelerating with just enough throttle opeing that you accelerate slowly, and that not being able to be in the perfect gear for the speed you are going is just a draw back of not having a continuisly varilable transmition.
I wouldn't however get up to highway speeds in 2nd gear, then go directly in to 5th, because there are points in there that you could be in higher gears then 2nd, alowing the engine to turn slower, so given the distance travled the engine would have turned over fewer times.
I would say that for going up a hill you should accelerate slowly befor the hill, and let the car naturaly slow down as you go up, then make up that speed going down the other side, if you take a bicycle out you can easly feel how momentum changes going up and down hills.
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Old 08-26-2007, 08:22 PM   #6
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I've found that unless I need to accelerate quickly, I can shift our 5 into the next higher gear at about 1700 rpm without drama. No matter what your useable rpm range however, it makes no sense to shift into a gear that prevents you from accelerating to your target speed. It works sort of like an exponential curve in reverse up to that point, with quicker acceleration just being available for the most of it.

I think, therefore I doubt.
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Old 08-27-2007, 05:53 AM   #7
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Based on my understanding of the BSFC ovals, I try to keep revs between 2000 and 2600 rpm, and engine load at about 75-80%.
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Old 08-29-2007, 08:49 AM   #8
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I accelerate through the gears at an engine load (100% in the case of my direct injected diesel) that provides the most power for some volume of fuel per minute (Brake horsepower Specific Fuel Consumption, or the previous BSFC acronym) while keeping close to the engine speed at which that maximum power output to fuel per minute input ratio is best (around 2000 rpm in my case).
However, once at my the desired speed, I get into the highest gear I can maintain. Even if that means foot to the floor acceleration (or the maximum possible without wheel or clutch slip) in 1st (idle to 2500 rpm), 2nd (1500 to 2500) and then shift into 5th (1000 rpm) to maintain the 35 mph I reached in 2nd.

Hill climbing techniques are dependent on the hill length, slope angle, speed limitations and such. Try to approach the base of the hill with enough speed to be able to maintain a steady accelerator pedal position and let the road speed fall off as altitude is gained. If done ideally, your right foot won't move, and your speed as you crest will be just above the speed at which you'd want to shift down a gear.
Long hills may necessitate shifting down anyway, as may truly steep ones.

Finally, climbing hills doesn't waste energy any more than acceleration does. It's the braking that turns that momentum into unuseable heat and dust.

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