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Old 06-05-2008, 08:15 AM   #11 (permalink)
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My thinking is that pulse up/glide down is better, because the fuel savings is achieved in the P&G technique by the glide phase. So extending or maximizing the glide would be more beneficial.
And sickpuppy has a good point about the aerodynamic penalty of pulsing down.
P&G may be an 'advanced' technique, but it's accessible immediately, unlike waiting for the weekend/spare moment to install the vac gauge to DWL.

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Old 06-05-2008, 09:07 AM   #12 (permalink)
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Quote:
Originally Posted by Tango Charlie View Post
I'm inclined (sorry ) to agree with you, but let me play the devil's advocate, for the sake of argument. 'Pulsing up' contradicts the 'ride like a cyclist' mantra. It puts more of a load on the engine, further decreasing efficiency. Is the 'glide down' enough to compensate?
Just have to point out that the above isn't true all the time, or maybe anytime for some of us. If your car has the HP to stay under 75% throttle in top gear going up the hill, it is more effecient to run the engine like that than drop a gear and use 35% throttle with more rpm. I didn't believe this until I got my scangauge but it shows that to be true.

I love P&G with hills, my 50.5km commute this morning had an average speed of 71km/h with a max of 110km/h gliding down a big hill, the speed limit is 80km/h. I got 6.0L/100km, 39MPG out of an automatic 95 Neon in light traffic.

The hills allow me to P&G in some traffic and get me to work with out any extra time and get nearly 1/3 better mileage(I use to average about 30mpg on the same route). I should note that this is engine on gliding too.

I have a couple of different route options that I can use. Some with more hills but more stops as well. The route I used today has the fewest stops and is in the middle for hills and is probably my most efficient route, sometime I'll have to try the hilliest route but it will take significantly longer but it might be the most efficient.
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Old 06-05-2008, 10:16 AM   #13 (permalink)
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Where the bicycle analogy breaks down is when you consider BSFC. Human legs are most efficient at any range of output. Car engines have a very peaky efficiency chart - very different. Driving the terrain like a biker is good, but P&G is better, because of this fact. If the car's engine was efficient over its whole range, it wouldn't matter. Metro can probably verify this with his Electric.
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Old 06-05-2008, 01:37 PM   #14 (permalink)
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I could verify it if I had onboard energy consumption instrumentation... which I don't, unfortunately.
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Old 06-05-2008, 01:46 PM   #15 (permalink)
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sorry. For you and for us.
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Old 07-07-2013, 11:31 PM   #16 (permalink)
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If you want to do a fun and educational experiment, do it on a bicycle.
You can wind thru your gears with less energy expenditure and peddle more efficiently going down hill. IMHO
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Old 07-08-2013, 03:41 AM   #17 (permalink)
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Quote:
Originally Posted by sickpuppy318 View Post
A higher peak speed (pulse down) would mean more of an aerodynamic penalty, right?
Sure - and drag is something you can't ever recover.
Drag, mechanical or aerodynamical, is permanently lost energy.
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Old 07-08-2013, 07:45 AM   #18 (permalink)
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It really depends on the grade and length of the hills. My local area has hills like Interstate overpasses. The hills get steeper when I go west. I've done a lot of local driving, basically living here for almost all of the 40+ years I've been driving. With the Fiesta's factory MPG gauge as well as the ones on my Altima and CVT first gen Insight (both sold and gone) I have developed some tricks to utilize hills for better mileage than perfectly flat ground.

Very gradual acceleration (in top gear) cost very little in additional fuel consumption. If the hill allows you to maintain your coasting speed then hit the top of that hill at the speed limit. That's about the steepest hill here, very few will allow the vehicle speed to increase above 45 MPH, so on any congested road I look for some drafting help to maintain my coast above 45 MPH.

Some hills require a completely different tactic. Thes are short duration but slightly steeper hills. On these I will gradually accelerate approaching the hill and go neutral coast up the hill and regain my speed downhill. My highest speed is close to 60 MPH (55zone) and at the crest of the hill that speed will drop to 40 MPH. This avoids the hit in fuel economy I would see if I just let the hill increase my engines load trying to maintain a constant speed. I regain most of my speed coasting on the down slope of same hill.

Other very shallow hills I will P&G on the upslope and even sometimes on the downslope. Again I am using very gradual acceleration, like 10 seconds to increase my speed by 5 MPH (faster on the downslope). This allows me to avoid any 10 MPH over situations where the roads are heavily monitored by the local police, while also not being too great an impediment to traffic.

In every instance I try to maintain a speed of over 40 MPH. In the Fiesta that is where it goes into 6th gear. I also try to avoid any load where the transmission shifts out of 6th gear at speeds over 40 MPH.

My speed peak and low points depend on surrounding traffic. If it's heavy I look for a big rig to fall in behind and pulse-draft. If lighter then I increase my speed differential range, but in both cases I try to avoid impeeding traffic flow. If someone wants to plant their nose up my rear end this tactic also serves to frustrate them enough so they pass me, just thinking I am an old geezer who can't drive worth a darn. Little do they know.

All the cars in this response were automatics. I need one in case the wifes car becomes undriveable for any reason, and with the congestion here you avoid crawling through a 1 mile 1 hour nightmare in a manual.

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Old 07-08-2013, 11:19 AM   #19 (permalink)
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It would seem that you are typically going to be staying in lower gears while pulsing/burning up a hill where you can quickly gain speed and get into higher gears while pulsing down a hill.
It is my contention that the car is more efficient gaining speed in a higher gear while going down hill thus storing inertia for the coming hill climb.

Here on the big island we will drive from Hilo to Kailua-Kona over Saddle road but in that case you have to just get up that mountain getting poor mileage but then you get to coast for miles and mile on the other side.
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Old 07-08-2013, 03:53 PM   #20 (permalink)
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Quote:
Originally Posted by esnap View Post
It would seem that you are typically going to be staying in lower gears while pulsing/burning up a hill where you can quickly gain speed and get into higher gears while pulsing down a hill.
It is my contention that the car is more efficient gaining speed in a higher gear while going down hill thus storing inertia for the coming hill climb.

Here on the big island we will drive from Hilo to Kailua-Kona over Saddle road but in that case you have to just get up that mountain getting poor mileage but then you get to coast for miles and mile on the other side.
The method you describe is not correct for most situations. You want to hold the highest gear possible that allows you to travel at a reasonable speed up the hill. This might mean pressing the throttle about 80%. It is more efficient than downshifting and using less throttle opening. Coast the downhill portion and supply some pulses if the grade isn't steep enough to maintain the speed you want. Much easier to do with a manual transmission.

Going over a mountain pass is very efficient since it acts like a long pulse and glide. You pulse up the mountain, and glide down the backside. I did this recently going from Montana to Oregon through some passes. My car is geared low, so I could hold 65mph in 6th gear going up, and then neutral coast on the backside. If only I had an engine kill switch, my economy would have been even better.

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