Non-hybrid coasting technique

Discussion in 'Fuel Economy' started by brick, Mar 8, 2006.

  1. brick

    brick Answers to "that guy."

    I'm driving a non-hybrid Accord with a manual transmission. Up until now (for years) I have tried my best to anticipate traffic and slow down without using the brakes. The thing is, I have always allowed the car to slow down in gear. This includes down-hill, coasting toward traffic controls, turns, etc. I used to think that this was the best way to do it since the injectors pretty much shut down in this state.

    I should disclaim that for the moment I'm not quite sold on ignition-off coasting. But even so, doesn't it make a whole lot more sense to take the car out of gear and let it idle while I coast vs. leaving it in gear? Not only does the car not slow down nearly as fast (if it does at all) but the overall friction losses decrease since the engine is turring at 1/2 the speed or lower. It seems to me that my overall consumption could be dramatically lower in the right circumstances. Especially if I can take my foot off the gas for long distances at higher speeds.

    Perhaps the optimal approach is a neutral-coast most of the time and engine brake when I know I need to reduce speed?
  2. tbaleno

    tbaleno Well-Known Member

    I think this would be best as well.
  3. philmcneal

    philmcneal Has it been 10 years? Wow

    see if you can use neutral to glide for a really long time, and at the end of that glide you KNEW you had to stop. Wouldn't it make sense to turn off your engine in the beggining of the glide? By the time your engine is on again, you've have had off for over a few minutes of a time.
  4. hawkgt647

    hawkgt647 Well-Known Member

    I would think the best coasting method would be engine off, in neutral. ( if you can tolerate it or if it's legal).
    Next best case would be engine running, in neutral.
    Next, engine running, just hold the clutch in. (short coasting, may wear the throw-out bearing over time)
    Next, coasting in gear, engine running (if the engine's fuel injectors are shut down) won't go as far, lots of pumping losses in the engine.

    A ScanGuage would help to show the difference using any of these methods.
  5. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Tim:

    ___I have absolutely no time to do much of anything until tomorrow afternoon but Tom, Phil, and Don and are dead on with their posts. I will try and post some pics in the gallery and add a few acronym descriptions besides those below so you can jump right in. Your Accord with a stick is going to do some absolutely miraculous things around town and will hold its own out on the highway after a few setup tweaks and a few changes in habits. Best mid-size car for hypermiling other then the upcoming Toyota Camry w/ HSD (TCH) and/or a year or so out, Ford Fusion hybrid (FFH).

    ___A quick note about ICE-On coasting … At ~ 30 mph in a NICE-On (Neutral-Internal Combustion Engine-On) with a warmed and completely setup Accord driving in 35 - 45 degree F temps, you are receiving in the neighborhood of 85 - 95 mpg. At higher speeds, the numbers pop up above 100 quite easily. You drop below 50 mpg at or around 10 – 15 mph in those temps with the same setup Accord. With the ICE-Off in a FAS (Forced Autostop), it is much much higher of course ;)

    ___Good Luck

  6. brick

    brick Answers to "that guy."

    Thanks for the responses guys! I added a sig with my vehicle's pertinent information in order to head off the basic questions about my setup. As for strategy, I'm planning to start off with the simplest methods first since I'm new to the advanced stuff. I started applying NICE-on coasting on the way home from work today, as well as a little DWL up the small hills. The commute is only about 9 miles so I won't have much indication of any progress for at least a couple of days. I didn't start any of this until 100 miles into my tank so I will be truly impressed if there is a detectable difference by half-tank. My scangauge shipped today and should take some of the guesswork out of it.

    So far so good, though. At least I managed not to hold up any traffic!

  7. psyshack

    psyshack He who posts articles


    Let us know how the scanguage works out for you and what you notice about basics concerning your Accord. I can share with you that our Accord coast circles around the Civic. But alas anything i do she rips apart in mpg in a matter of a few short miles.
  8. brick

    brick Answers to "that guy."

    Just for fun I thought I would post some initial observations after my first 30 miles of attempted hypermiling.

    On the pleasant side of things, the Accord really does coast better than I would have expected. More often than not I will overestimate how fast I need to be going when I put it in neutral with a particular target (such as an intersection) in mind. It's going to be really nice to swap out the winter tires for the summer wheels/tires and get them properly inflated.

    I have also noticed that I have better luck timing the traffic signals when I'm driving at or below the limit as opposed to the five or ten over that I had been doing along with everyone else. It tends to work well when I can see a red signal in the distance and start coasting, sometimes allowing me to keep some valuable KE through the intersection rather than stopping and starting again. Once in a while someone will even follow my lead at a fair distance!

    On the down side, DWL can feel downright wierd compared to normal constant-speed driving. My brain knows what's going on but my gut thinks something is very wrong. It also isn't particularly viable when there is traffic behind me and no passing lane. Unexpected speed transients can be very bad so I'm sure I will be forced to sacrifice a few MPG there.

    My scangauge will definitely be waiting at the post office tomorrow. I have a feeling that it will be essential to optimizing when I put my right foot down and how hard. Same goes for gear selection, since I'm never really sure if I would be better off cruising in fourth or fifth at transitional speeds around 45mph.
  9. hawkgt647

    hawkgt647 Well-Known Member

    When you do swap out the tires, think about trying the max pressure printed on the tire sidewall. You will give up a little ride comfort, but the FE gains may justify it.

    As long as you're not "lugging" the engine in too low of an RPM range, the taller the gear that the engine will pull should be the best for FE. Again, the ScanGuage will help here.
    My Insight will pull 5th with the RPM's at 1050 or so. And making very small moves to the throttle, you can accelerate. It just happens in slow motion.:)
  10. gonavy

    gonavy Well-Known Member

    oh you guys with sticks. I'm jealous. (Not in that way) I can only dream about FASing ...

    Over the winter, I started to play with the neutral coast (engine on) vs foot off gas in gear (injectors shut, per my scangage). Of course I don't roll as far, but it seems (not rigorously tested out) that my FE ends up being ~the same.

    Remember- the HAH has 3 cylinders sealed for lower pump losses, but IMA is generating away during an in-gear coast. In neutral, all 6 cylinders are firing away. So my HAH results may be one-off from normal AT vehicles.

    Although I coast further in neutral, the engine is consuming fuel, and autostop never engages in neutral, forcing a manual stop. This is in contrast, and apparently balanced, with driving longer, coasting less, but consuming zero fuel during the coast and AS still engages at the end. All of these are on the scale of 100ft to 1/4 mile- everything from upcoming stops to simply eating/extending the buffer to the next car on the hwy or coasting a hill.

    All I can conclude is that the FE difference is small between these two methods in the HAH. Which you use depends on the slope of the road, how far you need to go, what speed you want at the end, how tired you are, etc.
  11. brick

    brick Answers to "that guy."

    A few more observations from today's driving.

    I only did about 25 miles of driving today but I tried to keep pushing it a little harder. I am starting to get more comfortable operating in this new mode, and I think that the energy flow is getting smoother. Anticipating how a coast will work out is getting a bit easier and I'm starting to get better about not building up extra speed unnecessarily. I still have no idea if I'm actually making a difference but at least I know I should be. This beautiful weather doesn't hurt anything, either.

    I am also starting to get over a few of my pre-conceived notions about driving anything but over the limit. First, I absolutely do not lose time vs. the rest of traffic. Probably four times out of five that someone accelerates past me off of a light I end up right next to them or immediately behind them at the next. Also, I don't find that I interrupt the traffic pattern. I was afraid that I would end up with a constant line of cars behind me but that just wasn't the case. In fact, a surprising number of people will just hang back even when there is an empty lane to pass. Apparently the average driver isn't quite as much of a lead foot as I thought?

    I'm apartment hunting tomorrow, which means the potential for 100+ miles of mixed driving. Should be fun. :)
  12. psyshack

    psyshack He who posts articles


    Dont worry about the traffic behind you. Thats there problem. In stop light to stop light,,, you have proven your point. I just love the ones that flip me off when Im in a hypermiling mode and we are at the next stop light door handle to door handle and they seem to think I need fliped off again as im setting there with ICE off. Thank God my wifes with me most of the time. She calms me down. In my gut I have no problem with breaking that finger and doing things with it thats un christian. Just like you,,, Im seeing more folks that will follow a slower lead here and there. Or they wont make the pass to exit in one mile like they use too.
  13. brick

    brick Answers to "that guy."

    With a little help from the ScanGauge I managed to find the answer to my original question about the best way to coast. I have been paying attention to the fuel flow readout as I move between the two modes: NICE-on and in-gear engine braking. My engine, when fully warmed up, burns fuel at a rate of 0.3gph while idling. MPG numbers during NICE-on coasting can be in the 100s. Originally I thought that it might be just as efficient or better to leave the engine in a very high gear during a descent because I assumed that the injectors closed, leaving the engine to pump only air. Not the case! Coasting in gear results in a fuel flow rate of 0.4gph-0.6gph and instant MPG numbers to match. So not only am I bleeding KE to pumping losses, but I am effectively dumping fuel overboard in the process. Why they would design the car to do that is a mystery to me. (If pressed I would guess emissions control.)

    Thus far I'm sitting at just below half-tank at 275 miles. (Half-tank was right at 250). The fuel gauge is fairly consistent and I haven't seen numbers like that since my long road trips last summer. But this is a mix of ~30% highway and 70% around town. What's more, I didn't even start applying any of the new techniques until 100 miles in. My next fill up at the end of the week is going to be extremely interesting! This really is like a game. The better the numbers get the harder I want to push it.
  14. hawkgt647

    hawkgt647 Well-Known Member

    Oh-Oh... sounds like he has the fever!

    Looks like with warmer weather coming soon, you should be getting your 10% increase easily.
  15. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Don:

    ___I can see a lot more then 10% coming from Brick on this tank alone. Wait until he discovers that thing called FAS … Oh boy, look out then :D

    ___Good Luck

  16. psyshack

    psyshack He who posts articles

    FAS rules!!!!!
  17. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Psy:


    ___Was it “Make friends with your FAST” or was it “FAS”? I love my FAS :D

    ___Brick, all kidding aside, if you have a stick, use it for what comes naturally when and where appropriate. Using 0 gph is the true way of maximizing FE. We don’t have a hybrid pack to rely on for propulsion in a FAS scenario of course but if you are coming up on the rear bumper of an automobile waiting for a light as just one of a hundred case studies, you really have to consider shutting her down and taking the free ride in.

    ___Good Luck

  18. brick

    brick Answers to "that guy."

    Odds are I will want to add FAS to my repertoir before too long. I can think of a couple of places on my daily commute where it would work pretty well. For example, the home stretch on the way to the office is at least 1/3 of a mile down hil in a 35 zone. Once or twice last week I managed to coast down that hill, through the left hand turn (got lucky with no traffic) around the parking lot and into my space without touching the throttle. So don't worry, your message isn't lost. :)


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