Calculating lbs per hour

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Shady16
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Calculating lbs per hour

Post by Shady16 »

Anyone have a formula to take injector size and the pulse width ms and covert it to lbs per hour? So if I add x number to the nitrous fuel I can use a formula to figure out the actual lbs per hour I'm using? I'm only concerned with fuel added not total fuel used. Thanks
LT401Vette
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Re: Calculating lbs per hour

Post by LT401Vette »

It is in TS, with the "Trip/Economy" Gauges once you set it up in the dialog:
Data Logging --> Performance and Economy Fields

I discovered TS was not logging fuel flow in lb/hr though, but that is corrected in the beta that was put up yesterday. So the beta will include Fuel Flow lb/hr in your data logs.

The raw formula isn't complicated either, but dead time should be taken out. How dead time is taken out is dependent on whether and MS1, MS2 or MS3
Phil Tobin
EFI Analytics, helping to simplify EFI
Next Generation tuning software.
Supporting all MegaSquirt versions and firmwares.
http://www.TunerStudio.com
http://www.efiAnalytics.com/MegaLogViewer/
Support the firmware running your engine:
http://www.msextra.com/doc/donations.html
Shady16
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Posts: 72
Joined: Thu Jul 31, 2014 12:47 pm

Re: Calculating lbs per hour

Post by Shady16 »

What's the formula? I want to know how many ms = how many lbs per hour added in the nitrous table. I have software that tells me how many lbs per hour needs to be added for x amount of pph of nitrous. Thank you for your time and the reply.
LT401Vette
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Re: Calculating lbs per hour

Post by LT401Vette »

It is basically just dutycycle * injector flow rate * number of injectors.

The only catch is you really want to use net duty cycle, which is based on PW - dead time.
The easy, but only ball park way to get that is to use PW-1. This assumes it is always a dead time of 1.0, so if you are just guessing your dead times this is probably about what you are using any way.

Assuming you are running full sequential so your injector is firing once every 720°:

netDutyCycle = { ( pulseWidth1 - 1 ) * rpm / 120000 }

If your running high duty cycles, this is probably close enough. If you have large injectors, the dead time error becomes a larger error in flow, but you still need accurate dead time values for it to matter.
You can make a more accurate netDutyCycle by doing a lookup of the set dead time which varies by volts:

Using an MS3 with current firmware and assuming you are using the same deadtimes for all injectors:

netDutyCycle = { ( pulseWidth1 - deadtime1 ) * rpm / 1200 }, "%" ;

or do the lookup local in TS to give the same results:

netDutyCycle = { ( pulseWidth1 - (inj2Open1 * tableLookup( array.opentimepct0, array.opentimev, batteryVoltage) / 100 )) * rpm / 1200 }, "%"

Now flow in cc/min is:
fuelFlow_cc = { (netDutyCycle * staged_pri_size * nInjectors) / 100 }

or in lb/hr:
fuelFlow_lph = { (netDutyCycle * staged_pri_size * nInjectors) / 1000.5 }


Now if you want to make it a step more accurate, then you might want to replace pulseWidth1 with an average PW for all the cylinders to compensate for any cylinder trimming you might be doing.

Again, though, this is all done for you if you turn on the Performance and economy fields in TunerStudio.
Phil Tobin
EFI Analytics, helping to simplify EFI
Next Generation tuning software.
Supporting all MegaSquirt versions and firmwares.
http://www.TunerStudio.com
http://www.efiAnalytics.com/MegaLogViewer/
Support the firmware running your engine:
http://www.msextra.com/doc/donations.html
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