[MetroMPG]

I got a message from someone who was curious how I got 95.x mpg over a tank in my 2000 Insight (that's the 2012-11-11 fill-up in my fuel log).

Figured I'd post a response here in the forum, because I'd rather have the info out there for others to see as well.

(Also... there are other Insight guys getting higher mileage than this on a regular basis. EG: Check out 3-Wheeler's summer tanks from last year.)

I'm in hilly part of my state so I thought that you may live in a much flatter region or you know something I certainly do not

Terrain/typical routes:

I do live in a pretty flat area -- all the driving on that tank was in south/eastern Ontario.

But that doesn't mean you can't get phenomenal numbers driving in hills/mountains -- it just requires different techniques than driving on the flat. (In fact you can do even better in hills, but you have to kill the engine on the downhill parts of your terrain, something the Insight won't do by itself, at speed.)

The majority of that 95 mpg tank (1790 km / 1112 mi) was covered in:

- decently warm weather over a span of about 3 months (Aug - early Nov)
- on lightly travelled secondary highways
- with a max posted limit of 80 km/h (50 mph).
- multiple trips, but none were short... most were ~200 km round trip

Main driving technique:

I rarely exceeded the speed limit. Sometimes I was below it (if it wasn't holding anyone up). But mostly I was trying to stay at the limit.

At that speed, if you pay attention to the Insight's instant fuel economy display (the graph) and adjust your right foot regularly, it's possible to keep it in maximum lean burn most of the time.

So, I was "target driving" (a.k.a. "driving with load"), with the goal of holding the instant gauge at or above 100 mpg indicated.

Minor driving techniques:

- Driving without brakes
- Engine-off coasting to most stops/turns (I installed a kill switch to do that.)

Aero & other mods:

The car had a number of aero mods in place as well:

- full upper & partial lower grille block
- passenger mirror deleted (see this thread about these mods which 'widen' the lean burn envelope)
- driver's side mirror folded back while on the highway (a round convex mirror keeps a smaller side view)
- hatchback wiper delete
- sometimes passenger or both front wipers deleted
- tires @ 55 .... not advised! You could die! (TM)
- electric power steering disabled .... not advised! You could die! (TM)

All these mods help reduce engine load and make it easier to achieve & hold lean burn mode at speed.

Very minimal use of electric assist:

I also have the hybrid/IMA inhibit switch installed (a.k.a. clutch switch or CALPOD mod). It fools the car into thinking the clutch is pressed (even while driving along), and it responds by disabling the following:
- electric assist (good),
- charging the hybrid pack from the engine, under most conditions (good),
- regenerative braking (bad).

I use electric assist sparingly. Why? Because when you take energy out of the pack, you have put it back in at some point. And the car may not necessarily wait for you to "refill" the battery by regenerative braking/engine braking.

And I don't want the car burning gasoline to recharge the pack via the engine while I'm cruising down the highway. You sure can't hold 100 mpg @ 50 mph when it's doing that.

So most of the time, I'm using juice from the hybrid battery to:
- re-start the engine (via the big electric motor),
- and power the 12v DC-DC converter when the engine is otherwise off (e.g. I do lots of engine-off coasting up to stops/turns).

In city driving, I'm regularly flipping the clutch switch on/off so I can capture energy with regenerative coasting or braking, then flipping it again to prevent assist. If I manage to fill up the battery through regen, I'll sometimes splurge and "spend" some of it with assist when its useful (e.g. climbing a hill while holding a high instant MPG).

Hope that helps!

PS: it's going to be significantly easier to get 90+ mpg tanks like this once I've sorted out the boat tail.

PPS: I wasn't sure whether to put this post in the ecodriver's ed section, or the ecomodding section. I picked the driving section because it's possible to get stupid high numbers in these same conditions from an unmodified Insight using driving technique alone. But you'd have to drive at a lower average speed than I do.