EcoModder Forum Alternative MPG Calculation

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 06-16-2022, 07:13 PM #1 (permalink) EcoModding Lurker   Join Date: Apr 2022 Location: Springfield OH Posts: 26 Thanks: 0 Thanked 5 Times in 4 Posts Alternative MPG Calculation I just wanted to verify my thinking and math with the tools I have. I run a Holley Terminator X and I can take logs of short trips and sections of drives. In the logs I can see my overall fuel flow in lb/hr and speed in MPH. I setup a spread sheet of a log of my daily commute to work and the average speed was 35.87 mph and found the average fuel flow to be 12.75 lb/hr for the whole trip. My question is the formula based on these values. I have been using this formula. Code: `(speed)/(fuel flow)*(weight of gas/gallon)` My understanding is a gallon of gas is 6.3lbs. In the above case I got 17.44mpg but at the pump doing the tradition calculation I have been multiplying the miles by 1.09. I have comparred the Jeep ODO to a GPS and the GPS reads higher by about 9%. So when I multiply the speed by 1.09 and do the calculation again, I get just over 19mpg. Does my barely passed highschool math check out or am I wrong? I have been making some lean tunes and so far the best I have gotten was 16mpg for the last 2 tanks using a corrected speed and 13mpg before that, so I am a bit skeptical I did this good.
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 06-16-2022, 07:25 PM #2 (permalink) マット     Join Date: Nov 2015 Location: Indiana Posts: 718 The Van - '95 Chevy Astro Cl V8 Swapped Team Chevy 90 day: 7.84 mpg (US) The new bike - '17 Kawasaki Versys X 300 abs Motorcycle 90 day: 71.94 mpg (US) The Mercury - '95 Mercury Tracer Trio Team Ford 90 day: 34.35 mpg (US) Toyota - '22 Toyota Corolla Hatchback 90 day: 40.11 mpg (US) Thanks: 131 Thanked 258 Times in 188 Posts Did you mention the average speed of 35.87 because that's all you have to work with? I see your thinking, but I don't think that would be a very accurate way of calculating it. __________________ 1973 Fiat 124 Special 1975 Honda Civic CVCC 4spd 1981 Kawasaki KZ750E 1981 Kawasaki KZ650 CSR 1983 Kawasaki KZ1100-A3 1986 Nissan 300zx Turbo 5 spd 1995 Chevy Astro RWD (current project) 1995 Mercury Tracer 2017 Kawasaki VersysX 300 2022 Corolla Hatchback 6MT https://www.youtube.com/channel/UC6s...LulDUQ8HMj5VKA
06-16-2022, 07:35 PM   #3 (permalink)
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 Originally Posted by M_a_t_t Did you mention the average speed of 35.87 because that's all you have to work with? I see your thinking, but I don't think that would be a very accurate way of calculating it.
I got all sorts of values I can use. I converted the data log to a excel spread sheet and there is about 40,000 lines of data that are roughly at 0.024 seconds per point. I attached pics of the different data points that are possible if setup. The Fuel Economy data point does not work on mine because it requires an electric GM trans that I do not have.
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 06-16-2022, 08:06 PM #4 (permalink) マット     Join Date: Nov 2015 Location: Indiana Posts: 718 The Van - '95 Chevy Astro Cl V8 Swapped Team Chevy 90 day: 7.84 mpg (US) The new bike - '17 Kawasaki Versys X 300 abs Motorcycle 90 day: 71.94 mpg (US) The Mercury - '95 Mercury Tracer Trio Team Ford 90 day: 34.35 mpg (US) Toyota - '22 Toyota Corolla Hatchback 90 day: 40.11 mpg (US) Thanks: 131 Thanked 258 Times in 188 Posts If you have it plot each point as a mpg number (instant speed / instant fuel rate) then average that it would be accurate, but probably the wrong units. It might be easier to have excel convert it to gallons/hr then plot it I thought maybe all you had were averages, which wouldn't necessarily give the whole picture. *I didn't look at your pictures since I am on my phone. I will when I get home though In case I missed something. __________________ 1973 Fiat 124 Special 1975 Honda Civic CVCC 4spd 1981 Kawasaki KZ750E 1981 Kawasaki KZ650 CSR 1983 Kawasaki KZ1100-A3 1986 Nissan 300zx Turbo 5 spd 1995 Chevy Astro RWD (current project) 1995 Mercury Tracer 2017 Kawasaki VersysX 300 2022 Corolla Hatchback 6MT https://www.youtube.com/channel/UC6s...LulDUQ8HMj5VKA
06-16-2022, 08:18 PM   #5 (permalink)
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 Originally Posted by M_a_t_t If you have it plot each point as a mpg number (instant speed / instant fuel rate) then average that it would be accurate, but probably the wrong units. It might be easier to have excel convert it to gallons/hr then plot it I thought maybe all you had were averages, which wouldn't necessarily give the whole picture. *I didn't look at your pictures since I am on my phone. I will when I get home though In case I missed something.

The only fuel flow I can get is in lb/hr. So how could I convert that to gal/hr?

 06-16-2022, 08:45 PM #6 (permalink) マット     Join Date: Nov 2015 Location: Indiana Posts: 718 The Van - '95 Chevy Astro Cl V8 Swapped Team Chevy 90 day: 7.84 mpg (US) The new bike - '17 Kawasaki Versys X 300 abs Motorcycle 90 day: 71.94 mpg (US) The Mercury - '95 Mercury Tracer Trio Team Ford 90 day: 34.35 mpg (US) Toyota - '22 Toyota Corolla Hatchback 90 day: 40.11 mpg (US) Thanks: 131 Thanked 258 Times in 188 Posts Divide by 6.3 (or whatever the weight of gas plus % ethanol is). __________________ 1973 Fiat 124 Special 1975 Honda Civic CVCC 4spd 1981 Kawasaki KZ750E 1981 Kawasaki KZ650 CSR 1983 Kawasaki KZ1100-A3 1986 Nissan 300zx Turbo 5 spd 1995 Chevy Astro RWD (current project) 1995 Mercury Tracer 2017 Kawasaki VersysX 300 2022 Corolla Hatchback 6MT https://www.youtube.com/channel/UC6s...LulDUQ8HMj5VKA
 06-16-2022, 08:51 PM #7 (permalink) マット     Join Date: Nov 2015 Location: Indiana Posts: 718 The Van - '95 Chevy Astro Cl V8 Swapped Team Chevy 90 day: 7.84 mpg (US) The new bike - '17 Kawasaki Versys X 300 abs Motorcycle 90 day: 71.94 mpg (US) The Mercury - '95 Mercury Tracer Trio Team Ford 90 day: 34.35 mpg (US) Toyota - '22 Toyota Corolla Hatchback 90 day: 40.11 mpg (US) Thanks: 131 Thanked 258 Times in 188 Posts If you only wanted the average for the trip/data recorded same you probably could have used the averages. Just use the average flow rate and average speed and the overall time to calculate total. So if you averaged 35.87 mph for one hour and 12.75 lb/hr (2.023 gal/hr) then you would get the average for the data. Which would be 17.7 mpg Sorry, I just realized that after re reading everything. If you do it the other way you would be able to see how your fuel economy was fluctuating and with some more math you could tell when and where you were getting the best fuel economy __________________ 1973 Fiat 124 Special 1975 Honda Civic CVCC 4spd 1981 Kawasaki KZ750E 1981 Kawasaki KZ650 CSR 1983 Kawasaki KZ1100-A3 1986 Nissan 300zx Turbo 5 spd 1995 Chevy Astro RWD (current project) 1995 Mercury Tracer 2017 Kawasaki VersysX 300 2022 Corolla Hatchback 6MT https://www.youtube.com/channel/UC6s...LulDUQ8HMj5VKA
06-16-2022, 09:04 PM   #8 (permalink)
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 Originally Posted by M_a_t_t If you only wanted the average for the trip/data recorded same you probably could have used the averages. Just use the average flow rate and average speed and the overall time to calculate total. So if you averaged 35.87 mph for one hour and 12.75 lb/hr (2.023 gal/hr) then you would get the average for the data. Which would be 17.7 mpg Sorry, I just realized that after re reading everything. If you do it the other way you would be able to see how your fuel economy was fluctuating and with some more math you could tell when and where you were getting the best fuel economy
Its been nice having these numbers since I can setup certain inputs to offset target AFR or ignition timing by flipping switches and I can see what has the best effect on fuel economy and just use averages of certain points instead of the whole log.

 06-18-2022, 05:19 AM #9 (permalink) EcoModding Apprentice   Join Date: Apr 2022 Location: California Posts: 166 Cx9 - '18 Mazda CX9 Grand Touring 90 day: 31.41 mpg (US) Prius - '10 Toyota Prius III 90 day: 57.8 mpg (US) Tundra - '00 Tundra V6 long bed base work truck 90 day: 19.4 mpg (US) Thanks: 95 Thanked 91 Times in 61 Posts Does your car return fuel to tank or is it returnless? If it returns fuel, does your fuel flow calculation account for that?
06-18-2022, 09:21 AM   #10 (permalink)
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 Originally Posted by Drifter Does your car return fuel to tank or is it returnless? If it returns fuel, does your fuel flow calculation account for that?
It is a return, and I am not sure how it calculated flow, but my guess is it takes a calculation based off of the fuel injector flow specs that had to be entered in manually or pick a preset factory injector part number, the fuel pressure, and the duty cycle of the injector. Mine is a return system with a regulator roughly 12” from the tank.