I remember the HCH being lower than the Prius and I thought more aerodynamic with a smaller cross-section. Also, Honda has a reputation for very efficient engines even though I knew the HCH didn't have the lean-burn. I was expecting the HCH having better high-speed performance than the Prius.

The HCH does do pretty good, even better than the Prius at 55-60 mph. What this suggests is something non-linear or unexpected is happening at speeds of 65 mph and above. This is something worth investigating to understand if it is engine, drive train or aerodynamic.

Actually the AC effect was perhaps a little high but it seemed to go away at 70 mph. But I'm not really interested in tuning AC systems.

No what bothers me is the shape of the MPG curve is wrong (see blue line below):

The HCH down-slope is more consistent with the onset of some non-linear effect. It would be interesting to find out the source.

Bob Wilson

 

Bob -

I think the speed vs MPG data for this 16 run test are okay and are fairly represented by the chart. The replicated runs seem to give low noise versus signal so I was fairly confident that the FE behaved as shown for the test conditions used. I dont know what the FE data would show above 70mph - probably lower, but I wont drive there anyhow...

To me, it would be premature to claim non linear or unexpected effects based on my test data.

The AC effect (at MAX AC) is what it was - more of a hit at 50 than at 70.

 

First, I want to thank you for providing excellent data. We've been mostly in the dark in this area and this bring enlightenment.
No argument from me! I've recently found that 68 mph is about the highest cruise speed I ever want to use for efficiency and hill climbing works best at 55-60 mph. I've been faster, up to 101 mph, to gather some engineering data but I don't recommend it.

We're in the same boat here. With my Prius, I'd noticed a sudden drop off from 70 mph to 75 mph. It turns out this corresponds to hitting the MG1 limit of 6,500 rpm that begins right at 70 mph. From 70 mph and above, the ICE has to run all of the time to generate power to keep MG1 rpm below 6,500 rpm. This causes a distinct fall-off in efficiency.

It is the steepness of the curve and the wrong inflection that has me wondering. What is going on above 65 mph?

Interesting, I'm not quite ready to look at tuning AC systems. Still, you've provided a valuable 'heads up' to our HCH community.

Understand I couldn't be happier to see this data because it gives us clues, insights, about were we need to look for further improvements.

Bob Wilson

 

I actually don't notice any change in my MPG from using the A/C in my HCHII.
The biggest change in my MPG comes from highway (which i do M-F for my work commute) to city driving (which I do on the weekend).

 

Thanks for all the feedback. I added a years worth of tanks FE vs outdoor temps (to the origional post). As others have found, there is a fairly strong relationship.