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Old 01-22-2009, 10:48 AM   #1 (permalink)
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Default Newbie qustion on lean burn and mileage

Hi, I haven't had my insight too long, but have had some experience getting good mileage on my Civic HX. I have been averaging 72 mpg on my current tank of gas, but have a question. I can tell when I get into lean burn mode, but is it better to cruise in lean burn in 4th gear or lower the rpm and cruise in 5th. Seems like at 40-45 mph or when accending a slight grade I can maintain lean burn in 4th gear, but not in 5th unleass I'm going faster or I'm on the flats. At 50 mph + I can cruise efficiently in 5th. So should I stay in 4th and stay in the lean burn mode as long as I can. From the readout, it seems like 4th gear is more efficient, contrary to what I've always believed. Also, is it better at times to use some IMA in a lower gear early to pick up speed when going up a grade and then ease off and upshift as you hit the crest. I can see why the guys with MIMA can take advantage of this. I rarely see my battery level go down more that a couple of bars. I don't push down on the throttle much. In my HX, I've always used my Scanguage, keeping an eye on the GPH and lose speed going up a grade til I hit the crest.
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Old 01-22-2009, 05:41 PM   #2 (permalink)
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Default Re: Newbie qustion on lean burn and mileage

Lean burn in 3rd gear produces better MPG than not being in lean burn even in 5th gear.

Generally try to maximize your time in lean burn... Secondary to lean burn is staying in the highest gear you can while staying in lean burn.

The exception of course is the pulse and glide method... but that is another can of worms all together.

And of course watching the road carefully and managing your momentum is yet another powerful technique.
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Old 01-22-2009, 07:32 PM   #3 (permalink)
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Default Re: Newbie qustion on lean burn and mileage

Thanks for the reply, I'll give it a shot
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Old 01-26-2009, 11:35 PM   #4 (permalink)
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Hi met-head; Iamian is correct, but there's more to the story. First, you need to maximize the envelope at which lean burn can occur. The main way to do this is to make sure you have lots of air in your tires. I run 55 lbs. And hopefully you have the stock Bridgestone Potenza 165-65-14 rubber.

By far, cruising in 5th gear is the most efficient. But to keep it in lean burn you may need to slow down to 58 mph or less, depending on the wind, the grade, and the tires, etc. A steady speed of about 38 mph is ultimately going to yield the very best mpg, but who has the time or patience to linger there very long? Therefore, everything else is but a compromise. But surely, accelerating slowly & gently, and staying OUT of electric assist yields the best MPG.
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Old 01-27-2009, 12:38 AM   #5 (permalink)
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I have a dashdyno that I set the alarms to light green when AFR/voltage
is reading lean burn and red when not. Its not as distracting as looking
down to see the fcd. When cruising its surprising how easy it is to
go in and out of lean burn with small hills.

From some trial runs I have increased the mpg about 10mpg by
using this device. With addition of MIMA I could keep that green
light on all the time and boost mpg a lot more. That might be the
next project after finishing the seat install.
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Old 01-29-2009, 01:44 PM   #6 (permalink)
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Thanks for the response. I run 40 psi in my tires, may try to add a little. One other thing I notice on my freeway commute to work, is that I can get up to 60-65 mph, and then get into lean burn and stay there, but my speed will gradually decrease to 50 mph over the course of about a mile or so. So then, I'll get a little assist and get back up to 60+ and do it again. This seem to be more efficient than keeping a constant speed. Also, I've been building speed before slight hills and let the momentum carry me over. One more thing, is it better to try and stay out of assist, using light throttle to maintain speed, or use it to pulse and coast. I am averaging 70-72 mpg
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Old 01-29-2009, 10:52 PM   #7 (permalink)
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Hi Met, If you add 5 more pounds to each tire, that is a total of 20 lbs. That will make a substantial difference in your rolling resistance. Your lean burn envelope will increase, and you will glide farther.

Yes, it is generally best to stay out of the pack (electric assist). Pulse and glide is excellent at lower speeds, (0-35 mph) and when there is little or no traffic. Also, you will likely find a 4-10 % increase in mpg this summer when temps are hot.
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Old 02-02-2009, 08:40 PM   #8 (permalink)
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I still have a lot to learn. On my commute to work, I was taking it easy and getting low -mid 70's. The other day, I did a lot of pulse and glide, and coasting and not using any regen and got 83 mpg going to work, but my SOC got down below 1/2. On the trip home it was hard to cruise without regen until the SOC got up to about 3/4. On the way home I only got 69 mpg, so I guess not letting the SOC drop below about 3/4 is the best compromise. Does this sound right? What happens if the SOC gets too low? Let's say, I'm going over the Cajon pass (10 mile grade up to 4000 ft getting steeper as you approch the summit) If I run out of assist, do I just downshift, or do I need to plan my attack speed so I just run out of assist as I clear the summit, and then regen? What's harder on the IMA battery, keeping it nearly fully charged, or a healthy discharge and then charge. I figure a lot of discharge or charge generates heat which is bad, I guess.
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Old 02-02-2009, 10:05 PM   #9 (permalink)
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All energy for propulsion in an Insight comes from burning fuel. The IMA system can only recover a relatively small percentage that would otherwise be lost without using regenerative brakeing or downhill coasting in gear.

The specifics for _best_ MPG on any given route vary, and are different based on the 4 T's. Temperature (weather in general too), Traffic, Terrain and Time on trip.

If you misjudge IMA SoC consumption, coast too much, fail to recover or use too much SoC, you'll fall into a forced charge and MPG will suffer.

You'll need to employ the 3 P's too, and let your MPG meter be your guide.
(Practice, practice, practice)

See:
https://www.insightcentral.net/forums...gmt-long.html?

for more than you probably want to know about the IMA system.

HTH!



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Last edited by Insightful Trekker; 02-02-2009 at 10:12 PM.
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Old 02-04-2009, 10:02 AM   #10 (permalink)
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Thanks for the reply. I think I was just trying too hard. My wife uses the car to go to work on occasion (to take advantage of the carpool sticker). She says all the dashboard lights just confuse her. So I tell her to drive it like a normal car and don't worry. Her commute is 100 miles round trip and she gets 60-62 mpg, so I can't complain. I can get 70-72 driving easy, keeping the the SOC almost full. When I try to get much more than that, I start losing SOC. Of course, at 50 mph on level ground, I can get nearly 90. My big test will be next month when we make our semi annual Vegas run. We run 60-65 mph to see what kind of mpg we can get. We usually take my Civic HX and have gotten a best 48 mpg. Last time we took our 5 speed PT cruiser with the rear seats taken out, tires at 40 psi, and got 35.0. I'm looking forward to see what the insight can do.
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