So,... in a nutshell, to hypermile...

Discussion in 'Start Your Journey Here' started by MinnesotaNice, Apr 27, 2012.

  1. MinnesotaNice

    MinnesotaNice Member

    I'm new to all this, looking at a lot of information about FE, etc. but I'm coming to a few simplifications to understand it. Tell me if this is right. (I was a physic major so... it guides my thinking).

    Basically, I'll get the best mileage if I either have the ICE off, in a coast or because I took my bike :). Or, I'm operating at minimum BSFC, probably rapidly storing up gas energy as kinetic energy (accelerating for later coast) since all cars are in a sense highly overpowered. We have a sledge hammer to drive a tack. The trick is then not getting arrested, kill by road rage, crashing, or having to hit the brakes wasting that kinetic energy.

    Other effects: weather, choice of route, managing engine warm-up costs, good maintenance, having "efficient hardware" to start with (engine, aerodynamics, rolling resistance).

    There's a question of choice of gear and average speed (in theory always at minimum BSFC), but that's kind of a trade-off of time to destination .vs. fuel used (i.e. time is money) because wind drag increases with (the square) of speed. We decide how much our time is worth .vs. fuel. Also, there's limited gear choices and manual or automatic control.

    Where is the minimum BSFC operating point (s)? It seems it would be helpful to have a procedure to map this out practically, then instruments to tell me where I'm at, say with a bar for rpm and throttle position, above or below minimum. Rather, it seems most people "hunt" for it with data clouded with all other effects, tracking instantaneous and averages of FE.

    In general, what features, describe a car best for pulse and glide as I describe it? (apart from "efficient hardware") A manual transmission with kill switch? Or key-in-ignition FAS? Some make/model hybrid? What size engine would it have? Once you completely put your driving behavior on the table to the point of advanced hypermiling techniques, it seems current hybrids are not right. They're better for people who don't want to change driving behavior (much). Or think about it. Of course, the "efficient hardware" tends to my hybrids.

    On engine size.... what if I had a prius chassis (say) with a tiny non-hybrid (what? 10-20 hp?) engine that was right at min BSFC in 5th gear (MT) and 60 mph? Any guess how long the acceleration would be up to 60? Even 60-90 seconds seems like overall, a great idea! It would be a bit of a social adjustment though!

  2. herm

    herm Well-Known Member

    BSFC is different for every engine, the rule of thumb is to keep the rpm while pulsing to 2000-2500, use a vacuum gauge or a scangauge to find that point.

    Dont forget the most important factor is the driver.
  3. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Super Moderator Staff Member

    You might be able to find the BSFC map for your car.

    If you can't just model it as a car with a similar displacement and cylinder count and then add some secondary terms to account for the difference in the engines. :D
  4. alvaro84

    alvaro84 Homura-chan's selfishness

    I think the smaller the engine the less it needs Pulse&Glide, I see this technique as an entertaining damage control for too strong engines.

    With that 10-20hp engine you mentioned you'd need quite a bit of power just to cruise at highway speeds, which means decent load (a better area of the BSFC graph). I may be doing it wrong (it's definitely possible not having any instruments to get feedback from)
    , but our 28hp 250cc bike (Ciliegia) doesn't really benefit from high speed pulse & glide while the 650cc 50hp one (Teresa) gets better FE when P&G'ing. I also think that at city speeds both vehicles can benefit from this technique (but this is just a theory, as I've never had (near) pure city tanks to draw any conclusions).
  5. MinnesotaNice

    MinnesotaNice Member

    I have the Mitsubishi 1.8 L 4G62 SOHC 8-valve engine. Multiport Fuel Injection. In a 1993 Expo LRV.

    Best BSCF estimate I found is this from here

    said to be "based on a sample of 1995 model year, naturally aspirated, EFI 2-valve engines. "
    The best BSFC is ...around 2000 rpm and three-quarters load.
  6. MinnesotaNice

    MinnesotaNice Member

    Exactly. Looking at the map I posted, more load generally puts you in more efficient islands.

    Right, and what if the cruise load was exactly in the center of the optimal island at 60 on the flat? It'd be perfect, optimal. My question is.... Could you, or How could you... live with it, the rest of the time?

  7. alvaro84

    alvaro84 Homura-chan's selfishness

    I think I'd use it a similar manner as I feel (but can't measure) with our smaller bike: steady speed on the open road, some P&G in the city, and definitely glide when I need to lose speed.

    Uphills maybe DWL would be the best choice: to remain at the optimal spot and gradually lose speed. When it's not too long, I suppose. There are many here who can tell you much more about DWL than I can.

    For steeper inclines I think that 10-20hp engine would need a lightweight chassis. And probably downshift to retain speed when you don't DWL.

    I don't DWL too much, though, it doesn't seem to fit Teresa too well. Light weight, too much power, insanely strong engine brake (without DFCO at the revs I use!) and bad aerodynamics tell me to P&G or keep the lowest possible speed in the highest (or second highest) gear. And glide whenever I want to slow down.

    (What I found the best so far was P&G in top gear, between ~70 and 120km/h [45-75mph], 2800-4800rpm - and it's not something I'd usually do on the rural roads I frequent. Here I use the pulse on the crest, glide down, hold bottom of 5th while climbing approach, with lower peaks (90-100km/h ~ 56-62ph is typical) and occasionally skipping P&G on flat, just stick to the bottom of 5th, or the 56mph speed limit when I'm on busy roads).

    Sorry if I'm not clear, it's my night shift and it's 5am here.
  8. diamondlarry

    diamondlarry Super MPG Man/god :D

    To me, wise use of kinetic energy, IE not wasting it, is the key to successful hypermiling. I strive to build just enough kinetic energy to get me to my next pulse point or the next stop sign. I always tell people to drive their car like they would ride a bicycle; build speed before uphills, coast down the other side, coast up to stops, etc.
  9. MinnesotaNice

    MinnesotaNice Member

    I've biked quite a lot, and that is how I think of it too. It just hurts to cram on the brakes on the bike at speed and have to pump it back up to speed. Like when light changes unexpectedly or an obstacle appears.

Share This Page