HCH-II - SAHM "Super Highway Mode" (70-90 MPG)

Discussion in 'Honda Hybrids' started by msantos, Jul 27, 2008.

  1. msantos

    msantos Eco Accelerometrist

    Yep, you read correctly.

    This mode is something I had a chance of trying on my last trip to HybridFest 2008 in Madison and may very well represent a big plus for those who do a lot of highway style driving. Coincidentally, Wayne (xcel) had a 2008 HCH-II on his hands during that same week and he was able to validate the evocation details and the results with pretty much the same conclusions. You'll find Wayne's impressions and conclusions regarding this mode on his " 2008 HCH-II for a week review Blog" thread.

    So, in addition to us now having a super-highway mode for the Prius II, we are now faced with a similar mode for the HCH-II and depending on your diligence you may be able to coax anywhere from 70 MPG to 90 MPG (2.6-3.3 L/100km). Please let us know if you manage to get better and for how long you can sustain it ;).

    And now, to formally introduce this mode ...

    SAHM (Super Atkinson Highway Mode)
    (you should have a Scangauge not only to evoke the mode successfully but also to keep it on for as long as possible ;) )

    How to evoke this mode :
    Set the ScanGauge to display the following gauges:
    IGN - Keep IGN between 30 and 36
    LOD - Monitor LOD values between 40-60
    MPG or LHK - optional
    Mode's operational objectives:
    Vehicle speed:
    50-65 MPH (80-105 KM/H)
    • To get it into the IGN 30, one must reach a steady target speed (ie. 55-62MPH) and then ease into the 50-55 MPG range (4.3-4.6 L/100km).

      • SoC must be at a good 7 bars in order for this mode to become available. The presence of 1 bar or hidden regen will deny you this mode. Drive for a short while and it will quickly become available.
      • Drive steadily for several minutes after a stop in order to get this mode back.
      • The platform must be sufficiently warmed up, preferably at stage 3 or better.
    • When the FE stabilizes simply lift the foot off the accelerator ever so slightly and then gently re-apply. This will have the effect of bumping the IGN up a notch into the mid 20's. If you notice the FE you'll see yourself getting bumped into the 60's (3.6-4 L/100km)or so.
    • At this point, lift the foot off the accelerator pedal again in the same way and re-apply. This last step will bump the IGN even higher into the 30-36 range. Along with that, the FE also climbs to the 70-90 MPG range (2.6-3.3 L/100km). Now the real test begins of keeping it in this range.
    To keep it in the second IGN bump, I monitor the LOD values since if they grow too high beyond, say 60, the IGN begins to drop... and if it drops too far then you literally fall off the SAHM mode.

    Conversely, if you lighten your foot too much, the IGN climbs beyond 34 and the chances of getting kicked out of the mode also increase.
    So the trick, (for me at least) is to monitor the iFCD , IGN and LOD and simply ignore the speeds. This should be pretty natural to many of us as this is basically the DWL technique.

    Ignoring the speeds actually worked very well for me as I could keep this mode on even as I climbed the smaller hills. Anything moderately steep or steeper and the LOD simply grabs you and pulls you off this mode. I suspect the grade logic control has a hand here too.
    Enjoy and and let us know how it works for you.


    Last edited: Dec 28, 2009
  2. msantos

    msantos Eco Accelerometrist

    New update:

    I just got some feedback (Thanks Paul) concerning the SAHM mode that finally confirms some other observations I had noted but was not sure of a couple of weeks ago.

    Apparently, there is one other important determinant that stands in the way of not only evoking this mode but also keeping it for extended periods of time: The SoC.

    In the simplest of terms, the SoC must be parked at 7 bars before this mode becomes lock-able... and it is not just any 7 bars but an adequate 7 bar SoC! This can be achieved by driving at a steady speed for a while and slowly the SoC will rest at 7 bars without much trouble. Once it plateaus at this level then the mode is easier to lock in on single IGN bump.
    Obviously, I was not sure about this on my last highway trip because I kept a steady SoC for the entire 731 miles of the trip. But I did notice that every time I emerged from a pit stop, locking the SAHM mode in was difficult at least until a few minutes later.

    I am going to be taking the family on a 4 hour camping trip to Hecla Island next week and I intend to double check on this while having the HDS station plugged in for the duration of the trip. Unfortunately, the Scangauge cannot co-exist while the tablet is on the ODB-II port, but I should be able to not only lock the mode in but also watch the SoC from a numerical perspective which is a better confirmation of the SoC's role in this mode.


  3. Harold

    Harold Well-Known Member

    Have you noticed any change with the ice tempretures climbing. Could this be hard on the cat. conveters and the valve system? ::(
  4. xcel

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

    Hi Manuel:

    ___The 08 HCH-II I had for a week allowed SAHM in a lot more regions than what your 06 and 07 must allow? I could enter into SAHM at basically any speed above approximately 35 mph and could hold while DWL. I could also enter it at any SoC from 4-bars on up. During one forced charging events from 4 to 6 bars, I was even able to hold it from the fifth to sixth bar! I was running 60 + in the Bridgestone Insignia’s which I think might help enter and hold SAHM easier them most even thought the car had less than 5,000 miles on the odometer.

    ___Below 35 mph, her RPM was in the 1,100 RPM range and I would see IG14/TPS 14 where she would hold that magic 100 mpg + range while just barely touching the throttle in the most gentle of DWL scenarios. I do not know if that helps?

    ___Next item. All my “in the driver seat pics” were completely unreadable. I will curse this Kodak until the day I die :mad: The next time you are out, could you have your wife take a snap of your SG-II while displaying English units from the back seat for the HCH-II review I have to start putting together? If not, I will try and get a test drive of an HCH-II from my local Honda dealer with my son in the back snapping pics of the ScanGauge showing SAHM.

    ___Harold, just my thoughts but there are no mis-fire events during SAHM so the CAT is not being stressed. In fact, I can almost bet it is as happy as it could ever be being fully lit and the exhaust gas flow is as small as can possibly be achieved before valve closure in EV-Glide :)

    ___Pack temps would not be involved here either because you are not drawing or filling 98% of te time you are “in the SAHM zone “ :D

    ___Good Luck

  5. msantos

    msantos Eco Accelerometrist

    Hi Harold;

    Not reason to worry. Under this mode, the vehicle is not only operating in a safe range of temperature and emissions wise but also on its most optimal FE range. As previously confirmed, this mode is not an anomaly but rather an implicit feature/behavior owed to the design characteristics of the power-plant.

    Hi Wayne:

    Good point, but I believe that is yet another mode altogether as the operational profile is somewhat different (as indicated by the IGN and other readings), but yet with similar iFE results. I personally confirm that engaging this low speed mode with a less than 7 bar SoC is definitely possible (as long as a forced regen routine is not under-way).

    The other odd thing I did not mention is that the "higher speed mode" seems to have (and some of us managed to somewhat confirm this), is that the RPM is not always a reliable indicator of mode's presence since it may easily vary from 1500 RPM to almost 2000 RPM without changing the iFE much.

    Yes, I will certainly do that. it should be much easier now that I actually have someone to hold the camera for me. :)


  6. xcel

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

    Hi Manuel:

    ___Thank you!

    ___The IG14/TPS14 at an RPM of 1,100 is what I believe both Tarabell, RHwinger and Bear15 see quite a bit on their own daily grinds. I was looking at the pics of Tarabell’s FCD(s) and tach (I have the larger originals from when we first setup that article) and saw the same thing in the review HCH-II at the lower speeds. It is definitely not SAHM given the IGN, TPS and speeds but it sure is nice to see it once the lights and traffic has been cleared ;)

    ___Good Luck

  7. msantos

    msantos Eco Accelerometrist

    That's the one.

    That particular low-speed-steady-state high FE mode is quite easy to evoke once the ICE warms up past stage 3. All you have to do is stabilize your foot after reaching the target speed and the PCM+ECU will do the rest. Around these parts we call it the "mid-3s" because when you have the iFCD displaying in metric the iFCD plants itself midway between the 0 and 6 L/100km into the 2.5 to 3.7 l/100km (65-94 MPG) FE zone. Keeping it there is also easy since all it requires is moderate steadiness on the foot .
    I am also guilty of squeezing that low speed mode for all its got on a regular basis during the summer months. During the winter months its another story as the ICE+PCM barely make it past stage 2. :(


    Last edited: Jul 31, 2008
  8. Dan

    Dan KiloTanked in post 153451

    So when are the Highway Tours going to begin?

    12.3 gal tank, + a 0.7 gal over stuff, + 77 mpg SAHM = 1000 mile SAHM range.


  9. msantos

    msantos Eco Accelerometrist

    Highway Tours? (sorry I feel like a decapitated chicken as I never heard of that before):D

    You mean... some kind of an FE/Distance challenge of some sort just to teach the pre-historic automotive press a thing or two about hybrids on the highway? :) Oh man, would I love that !!!

  10. xcel

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

    Hi Dan:

    ___As you noted, this is one of the areas where an HCH-II can walk over a Prius-II. And it can be held up to 60 mph albeit at an ever lowering mpg as speeds climb. In any kind of stop and crawl or impediment laydened segment, I would sometimes curse the efficient girl because she wasn’t a Prius :(

    ___Manuel, why don’t you work on your Honda connections up North as the Canadian press always has some kind of cross the country challenge going on. Who better to take an HCH-II across the Continent on less than 3 tanks of fuel in the summer :D

    ___Good Luck

  11. Harold

    Harold Well-Known Member

    Thank you ,to you manuel and exel. H:)
  12. msantos

    msantos Eco Accelerometrist


    That would be a memorable challenge for sure... and I would love to do it just to see the look on my wife's face (she would think I finally went crazy) :D

    Lets see:
    From Halifax to Vancouver with at least two drivers and one car, and... assuming that we do get avg 77 MPG we would need at least 4 fillups for these 12.4 Gallon tanks ($5.5 USD/Gallon, this year's Canadian gas pricing):
    If we got a 70 MPG avg, then 5 fillups:
    If we got a 65 MPG avg, then at least 5 fillups:
    Thinking cap on:

    A partnership with the automotive press (yuk, they do this regularly) would definitely not work as they are all chronic lead foots. I think many of them would rather pick a voluntary lobotomy instead of driving for so many days with a focus on FE. :(

    Getting press coverage from the general media would not be a problem as that would be a simple matter of making half a dozen phone calls. Then, we would just have Honda Canada wire a short press release a day before the event to nail the remaining press channels.

    Anybody want to ride along in a challenge like this ? :D :D


  13. xcel

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

    Hi Manuel:

    ___Let us say we can filler er up with 13.2 gallons and I know of at least one volunteer... And possibly 10 more ;)

    ___Good Luck

  14. Harold

    Harold Well-Known Member

    The Rockies may throw a wrench into the ointment!!! But it is fun dreaming? ;)H
  15. msantos

    msantos Eco Accelerometrist

    Hi Harold;

    It sure throws a big wrench into it, all right. I figure that in total we have roughly 611 miles worth of agonizing SoC/RPM pain and suffering ;)


  16. psyshack

    psyshack He who posts articles

    To me,, this sounds like what I do daily. Pulse and bleed cycle. Even in the Mazda I can see several miles tick off at 72 mpg until load becomes unmanageble. Then its all gone.

    I don't have the SG in the Mazda. but do use the hacked DIS. Its slow. but does work. The Civic use to post up numbers in the high 80s to low 90 mpg range if you got it in a super hwy mode.

    Wayne,,,, how does the Accord respond to this type of driving? I will see what our Accord does next week when I get to drive it.
  17. Mr. Kite

    Mr. Kite Well-Known Member

    Based upon my experience from the 5 times I've topped off my HCHII, you can get about 1.9 extra gallons in by topping off. The most gallons I put in was 14.035. I assume it was pretty close, but I didn't run it dry.
  18. xcel

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

    Hi Jeff:

    ___The SAHM is not a DWL/DWB bleed off and pulse but a DWL/DWB steady state cruise with the iFCD in the 70 to 90 range up to at least 60 mph. I did not go much over 63 mph using it the entire time I had the HCH-II but you keep losing 5 mpg pips the faster you go ;) The Accord will hold 52 mpg at 52 mph but the HCH-II is worth a lot more.

    ___Going back to my first 80 + degree segment to downtown Chicago and back, she allowed 82.2 per the FCD which is low by 1.5 to 3 mpg vs. actual. This was pre-rush so the roads were still relatively wide open and this is where she shines. 45 – 60 mph, IGN 29 - 36 and a TPS of 17 or so. Keeping LOD under 50 is a must as well. I keep forgetting about that as Manuel has described throughout the forum more than a few times.

    ___Good Luck

  19. owlmaster08

    owlmaster08 Well-Known Member

    Hum, and I thought i didn't need a scangauge for my HCHII since it had a tach already...

    $170 only to achieve SAHM...
  20. msirach

    msirach Well-Known Member

    I achieved the super highway mode on my way home this morning WITHOUT the Scangauge. I could keep it in o.k. at 40 to 45 mph, but around 55 mph, I couldn't keep it in. Using the Scangauge though had taught me "the feel". I'll be traveling with the Scangauge again tonight.
    It won't cost you $170 though. You can get in on the group buy for $20 less.

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