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Discussion Starter #1
Hi,
Has anyone devised a way to allow the US CVT to enter lean burn? If so, what modifications/changes need to be made?

Thanks for the help!
 

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Well, there have been posts over the past that discuss this topic, and have implied that same conclusion: go buy a 5-speed!
"Due to extra load of the CVT, the lower compression ratio, and other hardware changes, lean burn isn't possible."

However, there are also those tantalizing hints of the JDM CVT Insights which, anecdotally, and also from posts from imported-to-the-UK-Insight-owners, have lean burn capability.

Could we try to summarize what lead to the divergence between the manual and the CVT versions in the US? Since the Insight was designed in the same environment as the earlier Prius, the EV-1, and the CARB mandates that eventually lead to PZEV, was the CVT Insight designed, starting in '00 or early '01, to satisfy California emission regulations as they might have developed over the next five years?

Did the emissions goals dictate the lower compression ratio engine? I'm not knowledgable enough to predict how higher compressions affects emissions. Does the lower compression engine allow for a wider, or narrower, range of usable fuel:air ratios before predetonation takes place?

So, what other engine/fuel/air changes did Honda make when putting the CVT into the Insight?

- different fuel supply and return lines to the tank
- presumably different code, and possibly a few different circuits, in the ECM to handle such things as manual transmission clutch switches, or serial TCM communications. (Since there aren't any shared pins that do one thing in an MT car, and another in a CVT, it would be worth checking to see if the electronics are identical. Go put CVT code in an MT-derived ECM and see if the CVT runs!)
- post 2002, measurement and use of the 3rd O2 sensor downstream of the NOx absorptive catalytic converter

Honda seems to have kept all the other major pieces of the system identical, judging by the Service Manual, such as:

- indexed spark plugs
- Air/fuel (1st) and O2 (2nd) sensors
- Three-way (1st) and three-way NOx absorptive (2nd) catalytic converters

My biggest question involves the air/fuel sensor and the absorptive converter. Why keep such expensive parts on a vehicle that would never use them to their potential? The risk of design changes late in the design cycle is a good reason - but I'd gotten the feeling that Honda is very adept at quick and flexible design changes. Maybe they just put an order in for 20000 of the sensors and cats in expectation of the Insight selling better than it did, and so they had ones that needed to be used. . .

In any case, one fundamental question that we can answer is this: how much power does the CVT consume in steady-state cruise at ~45 mph, and over what power ranges will a MT stay in lean-burn? If the two overlap, derating the MT power by some fraction due to the lower compression ratio of the CVT, then the CVT could productively run in lean burn.

Another question I haven't seen addressed is this: what actual part number differences are there between the JDM Insights and the US CVT Insights? Should someone have access to the Japanese microfiche (or to a JDM Insight), that's a key question to answer.

One other thing to look at are the differences in wiring to the CVT and the MT ECMs. Using the Service Manual as a reference, they aren't major. They're almost all directly related to the transmission - shift lock switches, idle stop switch, 5VDC to the TCM, transmission position switches, TCM serial comms, and shift up/down light. There is also the 3rd O2 sensor used on the 2002-> MT cars.

This suggests that piggybacking two ECMs, one CVT, and one MT, would be a solution. Send all the signal inputs to both ECMs (hoping that the double load won't pull the signal lines down, otherwise, a buffer box will be needed), and make a Y-harness that pulls the transmission control signals from the CVT ECM, and the engine control signals from the MT ECM. Throw the 3rd O2 sensor and harness downstream of the NOx cat. Decide which ECM gets to run the check engine light. Build one Y-input and one Y-output wire harness to the ECM, and add one MT ECM, and let us know how it works!

Another, more fundamental way to do it would be to take a guess at Honda's lean burn logic and emulate it. What do you think they use? It probably uses all of the engine sensors to determine commanded engine power, decides on possible engine power given the environment, makes the lean burn decision based on that, and then goes lean burn until the knock sensor or excessive desired engine power pull it back out of lean burn.

Could we just use similar simplified logic as used in the turboed Insights? Simply shortening the injector-on cycles, controlled by the air-fuel sensor, and lengthened by the knock sensor, would be a basic method.

Making a CVT go lean burn seems to be an academic exercise. However, like I mentioned, I'm most interested in why Honda didn't keep the lean burn available in the US cars. What I see is that it's technically feasible, but was probably not designed in, so that the CVTs had low emissions not essential to the Japanese market.

-Jeff
 

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Some may find it interesting to know the effects of Lean Burn on the Gasoline Engines Efficiency.
But either way the Insight's peak engine efficiency during operation is higher than most car engines.
Also remember this is not the net vehicle efficiency just the engine itself converting fuel energy to motion.

 

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Isn't lean burn.... less.... needed... in a CVT?

In the MT, you get 5 speeds... just five.
What if none of the 5 is the "perfect match" to deliver the power you need in the most FE manner?

In the CVT, the car can lower the RPM at any MPH to reduce fuel consumption.
A 5-speed can't do that... so the 5 speed leans out to reduce power output and reduce fuel useage.

Also, in the 5-speed, I've learned that lean-burn is not just "on or off".
There are many shades of "lean".

The A/F can be 16:1, 18:1, 21:1, 24:1 or anything, in-between.

The CVT has nearly "infinate" gear ratios.
The MT has nearly "infinate" air/fuel ratios.

So what is the real reason the CVT gets lower MPG?
It could all be from extra weight, and extra friction.
You get lower MPG in all automatics, don't you? Cars without "lean-burn".

I can picture it now... you modify your CVT to do lean burn, and then to maintain speed, your RPM goes way up, and your MPG is back to where you started at. I havn't proven that is true... I just said I can picture it.

When a car maker puts a different model in a different market, in small numbers like this, we may never know the reason.
It may not have been "better", It may have been cheaper, or they themselves wanted to experiment, who knows?
 

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Insightful Trekker said:
Ian,

It would be nice to know where your quote is attributable to. Link Please?

And maybe shrink the font size in the quoted box. It scrolls off to the right and is unreadable.
The EPA document number is included in the picture I posted above along with the release date of the report... it is at the bottom ... sorry you missed it.... or are you just spoiled with people providing point and click links for you?

The original was a PDF I posted a picture of the text from the pdf as an easy way for me to post it without retyping everything.

As a picture it does not have a font size to change.... it does not overlap or go over on my screen.

As a picture you can right click on it to make it a full screen or to save it.

The original paper is 50 pages long... I have uploaded a copy to my web site you can see / read it here:

Nice point and click link follows ;)

http://www.geocities.com/ian_p_george/420d04002.pdf

The picture of the text that I took is from page 17.

I think it is interesting how the Insight in lean burn is pretty much just as efficient as a diesel engine even if the Diesel fuel still has more energy than a equal amount of gasoline does.
 

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IamIan said:
.... or are you just spoiled with people providing point and click links for you?
Who me :?: :badgrin:

Yes, I missed the "code". (and wouldn't have gone on the expedition to try and decode it (see answer #1 above :badgrin: ))

Thanks, Interesting bit of data. :)

gpsman1,

Sorry wrong answer. It was done as an emissions reduction option. A CVT meets ULEV requirements whereas a 5 speed does not.

IIRC Japanese version CVT's are "lean-burn" equipped.
 

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Discussion Starter #9
Thanks for everyone's info on the CVT lean burn question. I was hoping it was as straight forward as switching out a computer box and presto...lean burn! If anyone as tried to replicate the Japanese lean burn CVTs or has any other thoughts I would appreciate hearing them.

Thanks
 

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Sorry for polluting your thread windham, thought you had long gone.

AFAIK its not a _simple_ task. At the very least a Japanese cylinder head and PCM would be needed. But IIRC the pistons might hold the key to the increased compression ratio. Lean burn is a fine line, a small window, and compression would play a large role in its function. Then there is the difference in O2 sensors. That's the short list. Getting it all to work might also require some other odd tweaks. And unless you can obtain a Japanese SM, are able to read it, looking for other potential pitfalls...

If the Insight had been produced in large enough numbers getting a "used" Japanese engine wouldn't be too difficult. There are import companies supplying the North American market with such right now. But I doubt they'd go to the trouble of searching for an Insight. Simply not enough markup and volume in sales for the effort (IF one could be found...).

IF you _could_ pull it all together you'd have a one-of-a-kind, with all the eventual glitches that any mechanic in his right mind would _run_ away from. Citrus Smoothie can tell you some stories about his Japanese import and the trouble he had getting a particular glitch fixed.

Save up and go buy a 5 speed. :)
 

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IIRC a couple of years back we had a member that was fluent in both English and Japanese. Only a few posts and not heard from since.

He did provide some information from Honda's Japan corporate site that wasn't readily available elsewhere, but alas there have been no reports on Japanese Insight enthusiast website(s).




For fisrt time readers of this thread also see:

Lean burn for Japanese spec CVT cars?
viewtopic.php?f=3&t=7880&p=69808#p69802

But this thread's discussion is more complete on the topic.
 
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