EcoModder Forum Pulse and Glide Fuel Economy Calculator 4 valve / Cylinder

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EcoModding Apprentice

Join Date: Dec 2007
Location: Melbourne
Posts: 152

The Mighty Mira - '92 Daihatsu Mira
90 day: 61.32 mpg (US)
Thanks: 0
Thanked 7 Times in 7 Posts
Pulse and Glide Fuel Economy Calculator 4 valve / Cylinder

Attached is my updated fuel economy calculator for generic 4 valve EFI engines. I've tidied it up a bit, and automated it so that most people here should be able to figure out how it works - I've really dumbed it down this time, no looking up BSFC values, you don't even have to google an air density chart, all you need is temperature and altitude. I assume dry air, but I did the calculations to adjust density for humidity and decided not to bother. Even at 30 deg C, and 100 degrees C, the difference is only 1.6% in air density. At 25 degrees, it's only 1.1%.

Note that it is available either as an ODS file in a nod to open formats, or in reverse engineered xls (MS Excel format). Either should work. Created in Ubuntu using Openoffice. Note that EVERYONE can use this spreadsheet for free, whether they have Windows, Mac or Linux. I suggest trying either gnumeric or openoffice.

Figures you will need to know:
Average speed during pulse and glide (assumes constant acceleration)
Total drop in speed until the next pulse starts
rpm@100kph
Drag Coefficient (google it, or do a coast down test)
Frontal Area
Coefficient of Rolling Resistance (use 0.06 for heavily pumped tyres)
Total Mass of Car (include driver etc)
Temperature
Altitude above sea level
Displacement of engine (or the idle fuel burn rate)

Note that you can unhide the rows to see my workings out and verify my equations, which I'd strongly encourage. Read my provisos as well.

Attached Files
 pg4vlvods.zip (60.6 KB, 126 views) pg4vlvxls.zip (54.3 KB, 133 views)
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"Every body perseveres in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed." - Isaac Newton

Last edited by newtonsfirstlaw; 12-11-2007 at 06:27 PM..

 Today Popular topics Other popular topics in this forum... View the most popular topics in this subforum by views or by posts
 12-10-2007, 07:18 PM #2 (permalink) EcoModding Apprentice   Join Date: Dec 2007 Location: Melbourne Posts: 152 The Mighty Mira - '92 Daihatsu Mira 90 day: 61.32 mpg (US) Thanks: 0 Thanked 7 Times in 7 Posts No comments yet? Let me know if anyone desires a two valve per cylinder version. It's a bit of a pain because the BSFC is not linear along a line of best fit over the best BSFC/rpm curve. The 4 valve per cylinder model was a gift. __________________ "Every body perseveres in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed." - Isaac Newton
 12-10-2007, 07:23 PM #3 (permalink) Dartmouth 2010     Join Date: Nov 2007 Location: Hanover, NH Posts: 6,427 Vegan Powa! - '91 Honda CRX DX Team Honda 90 day: 66.52 mpg (US) Thanks: 92 Thanked 114 Times in 82 Posts I just got a chance to play with it, very cool! Seems like gearing makes a large difference in my case (as I would expect). Think about making a web version? __________________ EcoModder's best: Donate to EM | Window clings | EM Shirts | Better Gas Mileage | MPG Tracking More fun sites: Green Home Improvement | crxMPG | Benjamin FT Jones | Vegan Recipes | Car-free Living
EcoModding Apprentice

Join Date: Dec 2007
Location: Melbourne
Posts: 152

The Mighty Mira - '92 Daihatsu Mira
90 day: 61.32 mpg (US)
Thanks: 0
Thanked 7 Times in 7 Posts
Quote:
 Originally Posted by SVOboy I just got a chance to play with it, very cool! Seems like gearing makes a large difference in my case (as I would expect).
Are you sure it's the gearing? Gearing is basically rpm @100kph. Did you change it from the base 4200?

My car is insanely highly geared (the defaults are for my car, and me), and a best case gearing for my car would be financially impractical IMO, the best I could do would be to increase tire radius by 15%, which might net a 9% gain at 100kph, lessening as I go slower. Going the whole hog would net me about 15% from memory.

Easier and cheaper to just take 20% longer to get to my destination, and travel at 80-90kph, and 100kph when I can't help it. At that speed, everything is working for me. Gearing is better, drag is way down, coasts are nice and long. It feels like riding around on a bike!

I can't help but think that there ought to be dedicated slow lanes on highways, where people can travel 80kph and not be pestered. It would open things up to vehicles like the Honda Cub etc.

If businesses were granted a fixed number of allotments where people could come to work and leave during morning and evening rush hours, traffic would be vastly improved and more efficient highway speeds would not result in more congestion. I used to hate the nanny state, but in this day and age it makes sense. At the moment the general population is behaving like a bunch of idiots, having feasts at the beginning of winter with the seed grain and the vegetables in the root cellar.

I wouldn't mind, but I happen to be sharing the same house with those idiots.

Anyway, I was thinking that gearing losses at speed might be useful. It would just be Loss = 100*[BSFCcurrent - BSFCbase)/BSFCbase]
Quote:
 Think about making a web version?
Not really, I like the open nature of ODF, and the fact that other people can double check my calculations (i.e. basic Open Source theory) so that other people can build on my work and everyone can benefit. Of course, someone else is free to do so. The equations are there.
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"Every body perseveres in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed." - Isaac Newton

 12-10-2007, 07:49 PM #5 (permalink) Dartmouth 2010     Join Date: Nov 2007 Location: Hanover, NH Posts: 6,427 Vegan Powa! - '91 Honda CRX DX Team Honda 90 day: 66.52 mpg (US) Thanks: 92 Thanked 114 Times in 82 Posts Interesting observations indeed. Of course speed was a huge factor for my car (more so than acceleration), but I was surprised at how much difference playing with gearing at 100kmh while driving at 100kmh changed things around. The only problem with dedicated slows lanes is that they would have to be cross by traffic to get in/off ramps and things, where the speed difference might make things unsafe, I think. __________________ EcoModder's best: Donate to EM | Window clings | EM Shirts | Better Gas Mileage | MPG Tracking More fun sites: Green Home Improvement | crxMPG | Benjamin FT Jones | Vegan Recipes | Car-free Living
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Join Date: Nov 2007
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Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

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90 day: 53.56 mpg (US)

Winter beater Metro - '00 Chevrolet Metro
90 day: 61.98 mpg (US)

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90 day: 58.72 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
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Quote:
 Originally Posted by newtonsfirstlaw Let me know if anyone desires a two valve per cylinder version.
Um, yes please. Will try out the 4-valve version shortly...

Ben: you've got 3 valves per, don't you?
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www.MetroMPG.com - fuel efficiency info for Geo Metro owners
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EcoModding Apprentice

Join Date: Dec 2007
Location: Melbourne
Posts: 152

The Mighty Mira - '92 Daihatsu Mira
90 day: 61.32 mpg (US)
Thanks: 0
Thanked 7 Times in 7 Posts
Quote:
 Originally Posted by SVOboy Interesting observations indeed. Of course speed was a huge factor for my car (more so than acceleration), but I was surprised at how much difference playing with gearing at 100kmh while driving at 100kmh changed things around.
One thing I forgot to add, this assumes that we are accelerating using 62% of available power, whatever throttle that is at. Deviate too far either way and there will be FE penalties. See the BSFC graph. Pick an rpm, and vary the load on the engine. The BSFC is efficiency, lower = better.
Quote:
 The only problem with dedicated slows lanes is that they would have to be cross by traffic to get in/off ramps and things, where the speed difference might make things unsafe, I think.
I think this is done in Germany already. Might be better to just slow down everybody to about 50mph/80kph. I almost can't believe I'm writing this - I used to go a bit above the speed limit religiously. But that's a very good compromise speed - lions share of the benefit, and still a fast speed.
__________________
"Every body perseveres in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed." - Isaac Newton

 12-10-2007, 08:07 PM #8 (permalink) Dartmouth 2010     Join Date: Nov 2007 Location: Hanover, NH Posts: 6,427 Vegan Powa! - '91 Honda CRX DX Team Honda 90 day: 66.52 mpg (US) Thanks: 92 Thanked 114 Times in 82 Posts I prefer slowing down to 285 kmh, by train! Anywho, Darin, I see that you're making a joke, I just don't get it, __________________ EcoModder's best: Donate to EM | Window clings | EM Shirts | Better Gas Mileage | MPG Tracking More fun sites: Green Home Improvement | crxMPG | Benjamin FT Jones | Vegan Recipes | Car-free Living
EcoModding Apprentice

Join Date: Dec 2007
Location: Melbourne
Posts: 152

The Mighty Mira - '92 Daihatsu Mira
90 day: 61.32 mpg (US)
Thanks: 0
Thanked 7 Times in 7 Posts
Quote:
 Originally Posted by MetroMPG Um, yes please. Will try out the 4-valve version shortly...
Urg. That's a bit of work. If someone feels like printing out the 2 valve engine map in the spreadsheet, drawing a line between (2000, 102) and (5200, 125), marking every gradation from 0.40 (estimated) at (2000,102) and 0.565 (estimated) at (5200, 125), i.e. 0.40, 0.41, 0.42, ... 0.56 by interpolating between the lines, and measuring where they are in terms of rpm, I'd be more than happy to write a lookup function to lookup the correct value.

I might do it later sometime though.

Until then, a useful kludge would be to go into the hidden columns and add 0.05 to the BSFC formula, for rpm at actual speeds greater than 3000rpm
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"Every body perseveres in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed." - Isaac Newton

 12-10-2007, 08:27 PM #10 (permalink) Batman Junior     Join Date: Nov 2007 Location: 1000 Islands, Ontario, Canada Posts: 21,827 Blackfly - '98 Geo Metro Team Metro Last 3: 70.09 mpg (US) MPGiata - '90 Mazda Miata 90 day: 53.56 mpg (US) Winter beater Metro - '00 Chevrolet Metro 90 day: 61.98 mpg (US) Fancy Metro - '14 Mitsubishi Mirage top spec 90 day: 58.72 mpg (US) Even Fancier Metro - '14 Mitsubishi Mirage top spec 90 day: 61.46 mpg (US) Thanks: 3,528 Thanked 6,319 Times in 3,269 Posts I'm OK with the kludge, too. Will report in later. __________________ Latest mods: 3-cylinder Mitsubishi Mirage. EcoMods now in progress... Ecodriving test: Manual vs. automatic transmission MPG showdown EcoModder has launched a forum for the efficient new Mitsubishi Mirage www.MetroMPG.com - fuel efficiency info for Geo Metro owners www.ForkenSwift.com - electric car conversion on a beer budget