Calculate your instantaneous MPG
09-12-2006, 12:17 PM
#1
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Calculate your instantaneous MPG
My theoretical calculation of MPG using MPH and MAF readings.
Ever since i purchased my scangauge, i've kept on eye on my MAF readings and engine load. THey told me things like 3.8 lbs/min and 19% load, which tells me how hard my engine is working but doesn't relate it to speed. So i set to work converting lbs/min of air into miles/gal of gas.
Fallow my work.
min ...... 14.7 lbs(air) .. 6.17 lbs .. 1 hour . miles ..... miles
------ x ----------- x -------- x ------ x ------ = -------
lbs(air) ....1 lbs(gas) ..... 1 gal ..... 60min . hour ...... gal
MAF A/F RATIO Density CONV. SPEED MPG
READING of gas
simplified out this comes to:
1.51165 x MPH
-------------- = MPG
MAF
Again this data is good but i don't want to have to calculate it while i'm driving so i made a table in exel.
My logic behind this is to find the speed at which my truck gets best MPG at on the freeway. I will do this by setting my cruise control at 55 MPH and record my MAF readings up to 75 MPH. Then look on my chart and see where the drop off is in MPG. So far it looks like it is around 72 MPH
NOw i know things like the F/A ratio can differ per truck and will mess with the calculations so this is something that could be improved apon.
Ever since i purchased my scangauge, i've kept on eye on my MAF readings and engine load. THey told me things like 3.8 lbs/min and 19% load, which tells me how hard my engine is working but doesn't relate it to speed. So i set to work converting lbs/min of air into miles/gal of gas.
Fallow my work.
min ...... 14.7 lbs(air) .. 6.17 lbs .. 1 hour . miles ..... miles
------ x ----------- x -------- x ------ x ------ = -------
lbs(air) ....1 lbs(gas) ..... 1 gal ..... 60min . hour ...... gal
MAF A/F RATIO Density CONV. SPEED MPG
READING of gas
simplified out this comes to:
1.51165 x MPH
-------------- = MPG
MAF
Again this data is good but i don't want to have to calculate it while i'm driving so i made a table in exel.
My logic behind this is to find the speed at which my truck gets best MPG at on the freeway. I will do this by setting my cruise control at 55 MPH and record my MAF readings up to 75 MPH. Then look on my chart and see where the drop off is in MPG. So far it looks like it is around 72 MPH
NOw i know things like the F/A ratio can differ per truck and will mess with the calculations so this is something that could be improved apon.
Last edited by allenmehrer; 09-12-2006 at 12:24 PM.
09-12-2006, 12:24 PM
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min ...... 14.7 lbs(air) .. 6.17 lbs .. 1 hour . miles ..... miles
------ x ----------- x -------- x ------ x ------ = -------
lbs(air) ....1 lbs(gas) ..... 1 gal ..... 60min . hour ...... gal
------ x ----------- x -------- x ------ x ------ = -------
lbs(air) ....1 lbs(gas) ..... 1 gal ..... 60min . hour ...... gal
09-12-2006, 12:42 PM
#5
Here's the equation a few of us collaboratively came up with on the EFI Live forum...
{SAE.VSS.mph}/({GM.INJFLOW.lbpm} * {GM.IBPW1} * {SAE.RPM} * 4 / 6250 )
in english...
mph /
(Injector flow rate in lbs per minute * injector base pulse width 1 * rpm * 4/6250)
6250 is a simplification of unit conversions... I forget the details exactly.
Works quite well.
{SAE.VSS.mph}/({GM.INJFLOW.lbpm} * {GM.IBPW1} * {SAE.RPM} * 4 / 6250 )
in english...
mph /
(Injector flow rate in lbs per minute * injector base pulse width 1 * rpm * 4/6250)
6250 is a simplification of unit conversions... I forget the details exactly.
Works quite well.
09-12-2006, 12:58 PM
#6
How do I change this text
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From th HPTuner boards......
I've used this and it seams to give a high reading for trucks....
Originally Posted by soundengineer
for a MPG PID
something like this might do the trick...not 100% sure..perhaps I'll play with it today some..
[SENS.20]/(([PID.6210]*0.132276)*[SENS.112]*[SENS.70]*8/6175)
then just make a histo that the x axis is the MPG PID..and select the MPG PID to log as well..
result should give you 1 box on the histo...and it will average as you drive....
would be nice to have better resolution on the MPH sensor like I talkek to chris about at one time
something like this might do the trick...not 100% sure..perhaps I'll play with it today some..
[SENS.20]/(([PID.6210]*0.132276)*[SENS.112]*[SENS.70]*8/6175)
then just make a histo that the x axis is the MPG PID..and select the MPG PID to log as well..
result should give you 1 box on the histo...and it will average as you drive....
would be nice to have better resolution on the MPH sensor like I talkek to chris about at one time
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09-12-2006, 08:18 PM
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RPM
MPH
Intake Air Temperature
Mass Air Flow Sensor Frequency
Mass Air Flow Sensor (lb/min.)
Engine Coolant Temperature
Injector Pulse Width (bank 1 and 2 if supported)
Long Term Fuel Trim (bank 1 and 2 if supported)
Short Term Fuel Trim (bank 1 and 2 if supported)
O2 Sensor Voltage (bank 1 and 2 if supported)
Manifold Pressure in PSI (Boost pressure for factory
turbo/supercharger applications)
Ignition Advance
Knock Retard
Engine Run Time
Battery Voltage
Transmission Temperature
Idle air Control Counts
Throttle Position Percentage
Throttle Position Voltage
Engine Load
Oil pressure (some 8 cylinder engines)
well this is all that i get from my scanguage
MPH
Intake Air Temperature
Mass Air Flow Sensor Frequency
Mass Air Flow Sensor (lb/min.)
Engine Coolant Temperature
Injector Pulse Width (bank 1 and 2 if supported)
Long Term Fuel Trim (bank 1 and 2 if supported)
Short Term Fuel Trim (bank 1 and 2 if supported)
O2 Sensor Voltage (bank 1 and 2 if supported)
Manifold Pressure in PSI (Boost pressure for factory
turbo/supercharger applications)
Ignition Advance
Knock Retard
Engine Run Time
Battery Voltage
Transmission Temperature
Idle air Control Counts
Throttle Position Percentage
Throttle Position Voltage
Engine Load
Oil pressure (some 8 cylinder engines)
well this is all that i get from my scanguage