Someone asked me how I got a 95 mpg US tank (2.5 L/100 km) in my Insight

[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.

[Frank Lee]

Sounds like you could ditch the electric assist equipment and come out ahead- less weight, expense, bother, etc.

[MetroMPG]

You're right. For a pure highway car (which is 90-95% how I use it), it probably hurts me a bit more than it helps.

But it's really nice to have a super quiet high voltage starter!

And even though I try to avoid the devil's pedal like the plague, sometimes it's not possible/practical, and then it's nice to be able to put some of that slow-down energy back into the pack. And then most of that stored energy gets spent later by the DC-DC converter when the ICE is off. Not for electric assist.

Also, the hybrid bits are great in the city for looking after re-starting the ICE after killing it. Shift into gear... automatic restart! Tap the accelerator... automatic restart! Deplete the brake vacuum reservoir... automatic restart! Turn on the climate control... automatic restart!

Not necessary, but nice.

And yes, all of those functions (except the high voltage quiet starter) could be looked after by a "smart" 12v system (with less capacity obviously). We're seeing just such 12v "micro hybrid" systems on more and more new cars.

[hackish]

How about this idea. Wire up an additional switch like the factory one for the brake lights that interrupts your hybrid disable. This way if you need to slow down you can engage the regen with light pedal pressure thus keeping the main pack topped up, or even gaining charge in it so you can selectively use the electric assist with no fuel economy penalty.

-Michael

[MetroMPG]

Yup, that mod exists.

Trust me - I'm never wasting an opportunity to capture braking energy -- I'm just doing it with the finger-activated switch. TMP (too many projects)!

But it absolutely could be automated.

[hackish]

I've been so thinking about having my company buy me a car and eco-mod the crap out of it. I'd love to develop a reflash for a prius to allow the user to customize some of its operation, like only regen the braking within certain pack limits and only use the electric assist under other conditions. This would also be very helpful for those who have added one of the larger supplemental packs.

Unfortunately before such a decision is made it would have to be studied to figure out if there is any hope of cost recovery. $25k for a car, $100k in R&D - could enough product be sold to cover that? Hard to sell something for to improve something 95% of its owners are already happy with.

-Michael

[IamIan]

Originally Posted by Frank Lee

Sounds like you could ditch the electric assist equipment and come out ahead- less weight, expense, bother, etc.

All depends on the usage of course.

There is always the weight, complexity, and cost penalty to the hybrid system ... but there are conditions there is offers benefits ... weather or not those conditions happen often enough to result in a net positive balance or a net negative balance to MPG is up to one's usage.

[Frank Lee]

As a flatland highway cruiser, hybrids don't benefit me.

The local auto junkyard had a damaged Insight but the #%^&& wouldn't sell it. I would have gone gas-only with it if there'd been any damage to any part of the electric drive.

[MetroMPG]

All depends on the usage of course.

Agreed. And for most drivers, under most conditions, the hybrid bits are a net benefit.

Also, on the point of driving without the extra torque from electric assist, I think most of those same drivers would find the car both woefully underpowered and over-geared without assist.

It's worth reminding folks of where I'm coming from: even without assist, my Insight has more power/torque than my Firefly/Metro (which I even "de-tuned" from stock by installing an "economy" cam, and then a taller final drive). And they weigh about the same.

So it all feels perfectly acceptable to me!

[IamIan]

Originally Posted by Frank Lee

As a flatland highway cruiser, hybrids don't benefit me.

The local auto junkyard had a damaged Insight but the #%^&& wouldn't sell it. I would have gone gas-only with it if there'd been any damage to any part of the electric drive.

One of my co-workers here in RI just bought a Gen-1 Insight for $2,700 ... a 2000 year with about 200,000 miles on it ... IMA battery code ... and didn't want to pay Honda what the dealer quoted to fix it ... so previous owner ran it as it was ( gas only ) with the error until the inspection lapsed ... not able to pass inspection as it was he sold it... luckily the error he got did not disable the DC-DC , just the IMA ( assist, Regen , Auto-Stop ).

So we reset / cleared the code ... and borrowed my grid charger ...IMA light hasn't come back in 2 weeks ... he passed his inspection ... so even if it does come back now ... he has the rest of the 2 year inspection to be able to run it as gas only.... it's a simple unplug two things and flip a switch.

Not a bad deal for $2,700 ... even if he only ends up running it as gas only... what other car could one buy for $2,700 that would do better? ... His personal MPG has almost tripled sense his old pickup he used to drive.

Originally Posted by MetroMPG

Agreed. And for most drivers, under most conditions, the hybrid bits are a net benefit.

Also, on the point of driving without the extra torque from electric assist, I think most of those same drivers would find the car both woefully underpowered and over-geared without assist.

It's worth reminding folks of where I'm coming from: even without assist, my Insight has more power/torque than my Firefly/Metro (which I even "de-tuned" from stock by installing an "economy" cam, and then a taller final drive). And they weigh about the same.

So it all feels perfectly acceptable to me!

yup ... as I recall down in the low RPMs ... where ICEs loose their power , but electric motors ( not so much ) ... the IMA motor can add up to something like about ~75% more torque than the ICE would have by itself around 1,500 RPMs... that is a big chunk ... A lot of people wouldn't buy a car with that much less low end torque ... even if they only use it less than 1% of the time.