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Old 28th May 2010, 08:24 PM   #16 (permalink)
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This is what I worked out.

Example. Injector is 380cc/min

So at 9% duty cycle that's 9% of 380 = 34.2 cc/min
Multiply by number of injectors, 6x34.2=205.2cc/min
Multiply by 60 to get hourly consumption 205.2x60=12312cc/hr
Convert to litres ,divide by 1000, 12312/1000=12.312
Convert to gallons, divide by 4.54, 12.312/4.54=2.71 gallons per hour.
Divide 60mph by gallons per hour to obtain mpg. 60/2.71=22.14mpg

If you want a quick way to calculate IDC from IPW at any given RPM, look here Stealth 316 - Injector Duty Cycle Calculation

Alternatively rpm x IPW / 1200 = IDC %

I did post these details on another forum and asked if anyone could confirm the validity of my calculations, but no-one did.
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Old 28th May 2010, 08:45 PM   #17 (permalink)
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Looks spot on.

There is a variable, the fuel pressure. It could swing 20psi. Thus varying the fuel volume a 20% or so.
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Old 29th May 2010, 10:55 AM   #18 (permalink)
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Quote:
Originally Posted by R32 Combat View Post
Looks spot on.

There is a variable, the fuel pressure. It could swing 20psi. Thus varying the fuel volume a 20% or so.
Hmm, yes. I had considered that, but without a fuel pressure reading there's not much I can do about factoring it in.
In an ideal world I would have fuel pressure and fuel flow readings, but this was just something I was thinking about when I was bored one day.
The inspiration for it was from thinking about some of my old cars that had "mpg" displays in them and how they had calculated it. Certainly, it's clear that there are too many variables for a truely accurate calculation. I did even consider going about making a box of tricks to display the values, but that's a little beyond my capabilities and probably taking things too far really.

Thanks for confirming my thoughts though. When you look at the figures, they're not too bad for a big old Datsun estate !
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