Basic P&G

Discussion in 'Fuel Economy' started by nissynis, Jun 13, 2008.

  1. nissynis

    nissynis NC Attorney

    I've scoured the site and found a great deal of information about the finer points of P&G. Might I ask the basic questions, though, with the hope that someone can answer or direct me to a P&G 101 thread?

    1) When is P&G to be used? As a replacement for steady-speed driving, right? That is, I should be thinking P&G if I would otherwise be cruising at a constant speed. ?

    2) What is the best delta, and the best avg speed for P&G? What kind of acceleration is appropriate for the pulse? The usual 3 mph/s?

    3) Why does P&G save fuel? It would seem to me that a pulse followed by DFCO would be inefficient compared to a steady cruise, because I would expend energy in accelerating that would exceed that needed to maintain a steady speed. On the other hand, I guess a pulse followed by a FAS w/ bump start would offer the benefit of having the ICE off for the glide portion, reducing the overall time the ICE is on for the cycle and saving fuel. That sure means a lot of FAS, though, a lot of FAS. (Maybe I should master the bump start -- just read a great post on how it is supposed to be a two-step process.)
     
  2. Vooch

    Vooch Well-Known Member

    first work on the easy techniques - try DWL for a week or so.
     
  3. kayasbluetaco

    kayasbluetaco Well-Known Member

    1) Yes... use in areas you would normally drive a constant speed.

    2. I do pretty quick accelration for the pulse, so that I am not burning fuel as long. My thought behind it is it makes sense that the pulse time is shorter than the glide time! And momentum of the quick acceleration would help extend it as well.

    3. Pulse followed by fas is probably the best. but I only use it on hills myself. Haven't braved doing it for a normal glide because I have too much traffic with me. But the bump starts make this an easier and more viable option because bump starting doesn't use as much fuel as starting with the ignition (as I understand) The reason pulse and glide saves you is because you may be burnbing more fuel for the accelration but you are using very little for the glide (none if fasing) so your average is better than it would be for steady... all I know is it really works :)
     
  4. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    Welcome, Nissynis!!

    1. Any time you have either steady speed driving or a series of stops you'll have to make. The stops are good because you can pulse to the speed that will just get you to the next point, then kill the engine and coast it in. Be mindful of traffic of course.
    2. The best delta is typically in the 15mph range. 10mph is also really good. 5mph is not so very helpful. P&G can be done at any speed but the really low speed stuff up to about 30mph can give some really eye popping numbers. I managed 73.0mpg in my Elantra over 17mi just over 2 months ago doing that. For an appropriate pulse aim for about 75% load or roughly 3/4 of full acceleration rate. This will require a slightly changing position on the pedal as you accelerate.
    3. P&G saves fuel because the engine is most efficient when under load. Steady state cruising is actually a very inefficient mode for the engine. Accelerating in the peak efficiency range of the engine will get you to speed most effectively and then you can average that (low) number up using the coast. You want your glide to be longer than your pulse if at all possible. This is an averaging game. Use the engine in its most efficient range, then turn it off. Yes, this is a lot of FASing but at higher speeds you will get almost the same results just using NICE-ON (engine running in N) because the idle fuel consumption is such a small percentage of the fuel needed to maintain the higher speeds.
    Great questions -- keep them coming!
     
  5. Shrek

    Shrek Kaizen Driver

    That is easy to explain and you can actually see the effect with a small experiment, but
    it explain better while looking at fuel per distance rather than distance per fuel, and as you do not have anything called Gallons per Mile I'll stick to metric:

    Drive at a rather high speed so that you are doing maybe 2500 rpm in top gear. Your iFCD will show maybe 6 l/100 km.

    On a flat or rather slightly descending stretch, reduce the accelerator pedal pressure until you can pull the gearshift to neutral without using the clutch, and instantly note the instant fuel-consumtion. On my car it might read 3 l/100km in this case.
    Then immediately drop the pedal so that the engine settles in idle, and note the consumption. In my case, maybe 0.7 l/100km

    This difference, 2.3 l/100 km is what it takes to keep the engine spinning fast enough to not slow you down, before it starts delivering net force to keep the car at a steady speed.
    There is so much resistance in the engine at cruising RPM.

    If you pulse&glide at a 10/90% rate, you would reduce that number by up to 90%
     
  6. 98CRV

    98CRV Well-Known Member




    1. I happen to be one who uses a 5 -6 mph delta range for the most part and it helps me a lot (doesn't mean that it will work well for others). Each car is very different, so let sgii help you do this.
     
  7. run500mph

    run500mph Well-Known Member

    I get huge numbers on flat long highway stretches using pulse and glide. I accelerate to about 75mph and FAS down to 45. Really long glides almost a mile. I get easily 48-50mpg on a car that is supposed to get 23mpg combined. I used to do steady state speed until Pale Malenesian told me how to do it. And yes 75% throttle is how to accelerate. No soft stuff. This is the trick that really made my mpg get really high. I used to do it in neutral, but FAS is where the real mpg's are.
     
  8. pumafeet10

    pumafeet10 Well-Known Member

    ok, here's my ? there are certain points on my route home from work where i go over an overpass, then down the other side and make a left turn to get on the highway with my ICE OFF. I m wondering if i should pulse and use the heavier accel up to speed or the slow since i am accelerating up from about 20 mph.

    Also at the end of my highway stint on my ride home i am going up hill on the off ramp and then back down to a stop light at the end of the ramp. most of the time getting a green light , BUT the left turn that i make is up a very steep hill . If i bump start it i put it in second and get about 20-23 mpg going up the hill with my acceleration light but enough to get up the hill. For this instance there is really no way to FAS since as soon as i would maybe 20 feet in im at a dead stop.

    Since this is pretty much my everyday route i feel like im stuck in a rut with figuring other ways to do it!

    David
     
  9. run500mph

    run500mph Well-Known Member

    Well, it all depends on if you can pulse before getting to the overpass hilll. If you can't pulse before, then do DWL (driving with load) which is what you described as going up the hill with as light a throttle as you can as you let your speed droop a little, then let off the gas at the top(or a light pulse at the top/crest of the overpass) and coast FAS or at least Nice-on to your left hand turn and beyond if you can.

    Now, for the end of your highway stint going home, if I understand this right, then I would pulse before getting to the offramp, and then coast fas all the way maybe throught the green if you can. Then as you go up hill after the turn, then either bump start or use the starter to keep going up with light acceleration. But at least you can sometimes get a bit of up the hill coast if you get the green. That's about as good as you can get there.

    Just remember, the more you FAS either on flat or other roads, the less time you burn.
    Can't do it in every situation but just do it as much as possible. Using the starter sometimes if you have to is no big deal. Hope it helps.
     
  10. wdb

    wdb semi-hyper

    I read your comment and a couple of others in other threads, and I just had a very interesting drive home. Same route as always, same speeds as usual, the big difference being that I was much more aggressive with acceleration during the "pulse" part of my P&G cycles. Previously I was acclerating in a gentle-to-middling manner, but tonight I tromped on it. While I normally struggle to break 40MPG, tonight I hit 50! Wow. That's a big enough difference for me to consider tossing in the occasional P&G (which I find to be a bit of a chore, and much less pleasant than setting the CC and listening to the radio) so that I can achieve my goal of a steady, reliable 40MPG on my commute.

    I tend to use a 10- to 15-MPH speed band, with the top of the band just wee a bit above the posted speed limit. Traffic conditions may cause that to vary, as does the presence of the constabulary...:Banane38:
     
  11. gershon

    gershon Well-Known Member

    I read here about using more throttle (70-80 LOD) on the pulse part of the pulse and glide.

    So, I went out and tried it first on an empty road between 31 and 39 mph and didn't look at the mpg during the pulse part. Just during the glide. My mileage went way up during the practice.

    Then I discovered it can fit in well with light city traffic. I tried to time my pulses so they would end on the crest of a hill and my glides for the downhills where I could FAS. It worked great. Now I don't think of them as red lights. They are opportunities to glide. Even getting a light red is not quite as big a deal if my engine is already off.

    By doing this, my MPG went up 4 or 5 mpg for a light traffic city route.

    After I finished the route, I found my average speed was 30 mph. Exactly what it usually is. Maybe someday, I'll drive that route without hypermiling and see how fast I go.

    My last tank was 47.4 mpg. Now I think 50 is possible if I P&G for a whole tank.
     
  12. tomw

    tomw Active Member

    I drive an automatic. How much throttle should I do on a pulse? Is it just enough not to have the tranny switch gears to a lower one, or more is better?
    Thanks.
     
  13. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    Tom, you definitely don't want the transmission to downshift when pulsing -- try to give it just enough to be right above that shift point and you should be in the right ballpark.
     
  14. nissynis

    nissynis NC Attorney

    I was suprised to read this. I had thought that a basic HM technique was avoiding "jack-rabbit starts." You are suggesting, however, that the engine is most efficient in the 2K-3K RPM range, while accelerating. I assume these are reconcilable. Is it because we are talking about acceleration in top gear? That is, there are two factors here: (1) being in the highest gear possible to minimize RPMs (the important principle when going from dead stop to speed), and (2) utilizing the sweet spot *within* a particular gear by nearly flooring it. Is that right?


    I am using a lot of FASing out there, and absolutely loving it. However, I do have a highway stretch in heavy traffic on the way home, and remain hesitant to FAS there. Which would be preferable: Pulse + NICE-ON Glide, or Pulse + DFCO Glide? With the former, the glides are certainly going to be longer, but at the cost of idle-consumption. The latter would have shorter glides but those glides would be free. I'm sure this is a solved problem with a clear answer....

    Thanks for the advice.
     
  15. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

  16. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    Nissynis, you shouldn't be in the 2-3K range unless you are on the highway. You want 75% load at the lowest RPM you can get with reasonable acceleration (and no lugging!).

    For coasting in a P&G regimen, NICE-ON is preferred. Only use DFCO if you actually need to slow down.
     
  17. run500mph

    run500mph Well-Known Member

    Oh yeah, good for you! I couldnt believe the change when I used p&g. I always coast fas and P&G now. I hit in the low 50's on a regular basis now. I like it because I used to drive steady and slow and didn't like it. Now I pulse up to 75 and coast down to 45 in my particular highway situation. The key was 75% throttle, not slow acceleration, which Pale Malenesian taught me. Enjoy the savings.
     
  18. Smile-n-Nod

    Smile-n-Nod Well-Known Member

    Why is that? In another post, I was told that when accelerating from a stop (in an automatic transmission), it's best to led the RPMs drop by lifting from the accelerator momentarily. Why should the transmission not downshift during a pulse?
     
  19. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    Both recommendations are saying the same thing. You want the transmission in as high a gear (lowest rpm) as possible, in all cases.

    (you may be confusing up and down shifting. By downshift, we mean when it kicks the rpm up a notch)
     
  20. Smile-n-Nod

    Smile-n-Nod Well-Known Member

    Ah, you're right. I didn't understand the terminology. Thanks.
     

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