[mjrogers]

There is no such thing as a free lunch.

Maybe I'm not getting what this concept means. I can't find 'lean burn' in the owners manual. I understand it to mean going at a steady highway speed where the assist kicks in for an extended period of time and the mpg becomes unbelievable. From reading this site there is a sweet spot where 'lean burn' kicks in.

My personal experience is that assist kicks in when accelerating or going up a hill at a steady speed. As soon as I stop accelerating, or stop climbing the hill the assist stops boosting the little 3 cyl engine.

Am I missing something?

 

[Guest]

lean burn

From my recollection, as I have passed through Davis, the hills are distant on the horizon :lol: I have been trying to keep the FCD display at the "75" mark and therefore in "lean burn". This is difficult and slow. I drove my return 22 mile commute last night at speeds 48-56 most of the way, occassionally at 65mph, did manage to complete the 44 mile round trip with a 71.2MPG, which is pretty good. previously I have achieved a 74mpg as a best, and more often 66mpg. So what I am understanding is the fuel mixture is more efficient in "lean burn", and I have to drive by the display at 75 or greater, and drive at slower speeds, to stay in the "lean burn" mode over the greatest distance. I have also not quite got the "assist" mode to work well for me, seems the MPG display will drop way down if I press the accelerator and go to assist up the many hills. Maybe the Assist mode is what I should strive for more, some sort of balance with Lean burn and Assist...

rodney
'03 silver MT no A/C
barefoot driver

 

[Armin]

what lean burn is and how to get there

There probably is a better explanation somewhere on this website, but I couldn't find it (is there a search feature? and FAQ?)

Anyways, lean-burn and rich burn are two distictive different modes of operation in the Insight's gasoline engine. It has nothing at all to do with the IMA. The lean-burn mode reduces the gas-fuel ratio significantly. (somebody who knows the numbers, please jump in). Lean-burn is only available in the 5-speed manual transmission model.

How to get into lean-burn:

Make sure your engine is completely warmed up, turn AC off, accelerate on a flat road in fifth gear to about 55-60 mph.

Now, reduce pressure on the gas pedal slowly and watch the instant-mpg bargraph to slowly rise one bar at a time. As I said, be gentle on the gas! When it gets to about 100 mpg, you will notice it suddenly jump up to 120 to 150 mpg. This was the activation of lean-burn!

Now, gently return the pressure on the gas, again one bar at a time, until you get to about 75 mpg. You are now driving in lean burn at the most power you can consistently get. If you press the gas further, just after the bargraph dropping to 70, it will suddenly jump to below 50, usually with assist coming on at the same time. You have returned to rich-burn.

The problem is the hysteresis: you need to get to above 100mpg to activate lean-burn, even though you can remain in lean down to 75 and sometimes 70-65 mpg. If you don't know this and just drive at 75mpg, the engine will remain in rich burn and use more gas.

 

[Motty82]

My experience is the same as Rodney’s. I try to keep the FCD display at 75 or greater to maximize "lean burn". "Assist" mode also seems to make little improvement on my MPG display as it still drops way down when I press the accelerator.

 

[Tim Maddux]

Armin's description of entering lean burn is very good... however I notice the jump sooner going right up to 75 mpg or so.

Once you're in lean-burn, the Insight dual catalyst system will start to fill up with NOx deposits. This will occasionally be purged as described on this page by the car dropping out of lean-burn and into rich burn mode:

http://www.insightcentral.net/encyclope ... lytic.html

This will also result in a slight power boost and corresponding dip in instantaneous MPG:

http://www.insightcentral.net/KB/faq-no ... ngineSurge

I have learned to compensate for this by lightening my foot on the engine pedal when the rich-burn kicks in, then dropping it my foot back down once lean burn re-engages. Its something I don't even have to think about anymore after driving the Insight for a couple years.

Another page talking about lean-burn air-fuel ratios:
http://www.insightcentral.net/encyclopedia/enlaf.html

This page also comments on no lean burn in CVTs. Honda's own tech specs state that the engine is the same, so I suspect that the lack of lean burn is due to the additional drag from the automatic transmission. This is supported by people who have stated they cannot maintain lean burn at highway speeds in a 5spd when they have put on tires with greater resistance. The Insight truly is engineered to a fine point.

 

[mjrogers]

Tim, you really di your homework

Tim Maddux said:

Once you're in lean-burn, the Insight dual catalyst system will start to fill up with NOx deposits. This will occasionally be purged as described on this page by the car dropping out of lean-burn and into rich burn mode

Thanks for the hyperlinks they were very informative. :mrgreen:

 

[benjamin]

Re: Tim, you really di your homework

Tim Maddux said:
Thanks for the hyperlinks they were very informative.

I'd like to add my thanks, Tim. You always make excellent use of our site. It's almost as if you know it better than I do! :wink:

Benjamin

 

[amplifiedmouse]

damn indiana for not having any hills for me to coast down. grrr

 

[Tim Maddux]

Re: Tim, you really di your homework

I'd like to add my thanks, Tim.

aw shucks. You're both quite welcome.

I learned most of what I know about my car from this website, and it was instrumental in my purchase decision 2 1/2 years ago. I'm glad I can give something back even if it is just links to the same great info.

 

[Will M]

For all this talk about lean burn, it doesn't seem like anyone has actually mentioned what it is. My understanding is that it is the special valve mode that was originally developed for the 1992 Civic VX. In that year, the Civic engine came with four different valve schemes:

CX = two valves per cyllinder. Everything conventional.

DX = four valves per cyllinder. The operation is conventional. They use four valves instead of two simply because within a circle (like the cyllinder head), you can get more surface area with four circles than with two, so you can move more air/gasoline mix in and more exhaust out more easily with two intake and two exhaust valves instead of one of each. My 1992 Civic is a DX.

VX = four valves per cyllinder with special hydrolics that will, on demand, disengage two of the valves, leaving one set of intake/exhaust valves closed while the others continue to open. This gives you less horsepower, but more complete combustion and substantially better gas mileage. The VX model Civic also had lightweight mag wheels (like the Insight) and the transmission was cranked so the engine was not revved as high at any given speed (like the Insight).

All the other versions of the Civic (Ex, Si, etc.) used the high performance version of the engine. This had four valves per cyllinder that would shift modes so that the two sets of two valves would alternate which one opened and which stayed closed. Since valves are a limiting factor on an engine defining redline, these high performance versions redlined closer to 12,000 rpm while the other versions redlined around 6,000 rpm. They got more horsepower and less gas mileage than the DX and the transmission was geared lower so the engine revved higher at any given vehicle speed.

The CX got something below 100hp (around 80, I think). The DX got 109hp. The Si and others got somewhere around 124hp. I forget what the VX got. Yeah, I was into cars then, too.

So, I think the "lean burn" mode is the mode where half the valves stay closed while the others do all the work. I witness it as a point when the gas mileage progress bar suddenly boosts about 20% and there's a very subtle sense of lessened horsepower. It takes a fine sense of touch on the accellerator to feel where this kicks in and out, and as others have said, on level ground, it is easier to do at lower speeds than at higher speeds.

 

[Tim Maddux]

Lean burn was pretty well-defined in the link I posted:
http://www.insightcentral.net/encyclopedia/enlaf.html

Instead of 14.7:1 air:fuel ratios the Insight engine runs as lean as 22:1 as noted here:
http://www.insightcentral.net/encyclope ... ngine.html

What you describe sounds like the VTEC-E system:
http://www.insightcentral.net/encyclopedia/envtece.html

which in one of the other links I provided to earlier mentions the activation/deactivation of the 2nd set of valves at around 2300 rpm.
http://www.insightcentral.net/KB/faq-no ... ngineSurge

Note that this happens regardless of whether you are in lean burn or rich burn, it's purely a function of RPM... though in 5th gear you have to speed a little bit to clear 2500RPM and that might knock you out of lean burn

 

[Rick Reece]

VX

Will,
I haved a 94 VX with 212K miles and it still runs fine (If the weather is bad then this is the car I drive). Most of your description sounds fine but the VX actually had 20hp more than the CX. CX 75 HP and the VX is 94 both 1.5L. I have a car and driver article where they explain the technology along with a road trip (LA to SF and back on a tank of gas). I believe they averaged 68 mpg but the car was EPA rated at 57. Interestingly enough the VX was a small percentage of sales (Made in Japan and a 2K option for the VTEC-E engine). Best option I ever bought.
The Insight definitely builds on this technology. The VX has an alternator that only charges when the engine has a low load whereas the Insight has no alternator but a DC to DC converter.
As a final point I can no longer get stock tires for the 94 VX. It used LRR tires but they are no longer made. On a bathroom scale (Hardly accurate) both the VX and Insight wheels weigh the same. Some day I will have to try that on a scale with more resolution. Have fun, Rick

 

[Insightful Trekker]

<replied inline>


Between all of us here we should be able to write the "encyclopedia" for the evolution of the Insight.

> For all this talk about lean burn, it doesn't seem like anyone has actually
> mentioned what it is. My understanding is that it is the special valve mode that
> was originally developed for the 1992 Civic VX. In that year, the Civic engine
> came with four different valve schemes:

CX <snip>
DX <snip>
VX <snip>

Don't forget EX or Si. Same valve train as the DX with a different lift/duration cam and maybe valve size(s). And a transmission to match.

><snip> Since valves are a limiting factor on an engine defining redline, <break>

Valve lift and duration will be the primary limiting factor in the attainable RPM of the mechanical capabilities of an engine. Unless you force feed it e.g. supercharger or turbocharger. The ultimate limiting factor is the liner velocity of the pistons/rings. At some point the pistons/rings simply due to the heat of combustion and friction will begin to weld themselves to the cylinder wall. As you approach this point durability becomes unsatisfactory.

> these high performance versions redlined closer to 12,000 rpm while the other
> versions redlined around 6,000 rpm. They got more horsepower and less gas
> mileage than the DX and the transmission was geared lower so the engine
> revved higher at any given vehicle speed.

What I remember of this bygone era was that no production version of any Honda had a redline above 9000.

Honda's evolution of the "lean burn" actually started way back in the late 70's I believe with their CVCC engines (Compound Vortex Combustion Chamber). Those engines were equipped with 3 valves per cylinder, 2 conventional and a 3rd CVCC valve. Initial combustion took place in a pre chamber then the CVCC valve opened the burning mixture into the leaner main chamber. It also required a 3 barrel carburetor with separate intake runners for the CVCC system. And ultimately enough vacuum lines to make you crazy when trying to isolate a vacuum leak.
This was done primarily as an emissions control design and allowed Honda to delay installing an exhaust system catalyst.

The VX model was (as I remember) Honda's first production model of their VTEC system (Variable valve Timing and lift Electronic Control)

http://www.leecao.com/honda/vtec/index.html

<snip>

> So, I think the "lean burn" mode is the mode where half the valves stay closed
> while the others do all the work. I witness it as a point when the gas mileage
> progress bar suddenly boosts about 20% and there's a very subtle sense of lessened
> horsepower. It takes a fine sense of touch on the accellerator to feel where this
> kicks in and out, and as others have said, on level ground, it is easier to do at
> lower speeds than at higher speeds.

I believe your mixing up lean burn with low output VTEC vs. high output VTEC. Agreed, no lean burn can occur in high output VTEC mode. But lean burn cannot be sustained even in moderate to aggressive low output VTEC mode. Its the chemistry and physics of combustion that simply cannot provide "lean burn" except within a narrow window of speed, load, acceleration, etc. The ECM constantly monitors vehicle conditions and "leans" the fuel mixture to the design limits. The system is capable of this because the mixture around the tip of the spark plug can be controlled close to the ideal of 14.7:1 air:fuel mix. The remainder of the chamber is progressively much leaner. Loose control of this and you'd get cylinder mis-fires and possibly pre-ignition. Continuous misfires can ultimately cause a CAT to melt down and fuse into a solid plug of clay in the exhaust system. A pre-ignition condition if sustained will inflict severe mechanical damage to an engine.

John K. Bullock
aka. Insightful Trekker