[Diy_efi] Base Fuel Calculations..

[Gregory Croft]

Wow..

Thanks for the formula. :)

For my 122 C.I. Engine, with 55lbs injectors..
I got a whopping 3.6ms pulse width. heh..

Very interesting..

I think I'll play some more with my fuel map and see what I can do. :)

Greg

----- Original Message -----
From: <Tlsalt at aol.com>
To: <diy_efi at diy-efi.org>
Sent: Friday, January 03, 2003 9:43 AM
Subject: Re: [Diy_efi] Base Fuel Calculations..


> Gregory Croft wrote,
>
> I am starting from scratch.
> I have a full stand alone system, and am figuring out both the fuel map,
and
> the ignition map.
>
> My unit doesn't do VE calcs, Just a spreadsheet like excel with pulse
width.
> It's a batch fire system.
>
> Unfortunately, I don't have any of the factory stuff. Daimler is pretty
> tight with their fuel maps for the neon...
> I have datalogged with an OBD-II scanner, but that doesn't report
> pulsewidth.
>
> I don't have any literature or formulas..
>
> Hello Greg,
>
> I suggest you get a copy of Jeff Hartman's book, it's a good starting
point.
> The formula he suggests uses cylinder displacement and estimated VE (at
peak
> torque) to calculate the weight of air in the cylinder and then computing
the
> weight of fuel needed using a target air-fuel ratio (12.5:1) and
converting
> to injector puslewidth based on the injector rating.  His method is a very
> rough guide, but I have used it and it will get you up and running so that
> you can start tuning the engine. You will have to estimate VE at the
torque
> peak rpm to calculate the highest pulse width and extrapolate the rest of
the
> fuel curve.  Try to get an accurate copy of the factory hp and torque
curve.
> If the injectors are properly sized, the idle pulsewidth will be somewhere
> around 2ms.
>
> Convert static displacement (cu in) to displacement at VE (est 80-90%
street
> engines).
> Divide cu in by cubic in foot (1728).
> Multiple by lbs air per cu foot (0.07651).
> Divide by number of cylinders.
> Divide by target air -fuel ratio.
> Divide by number of injections per power stroke.
>
> Equals= lbs fuel per injection(A)
>
> Divide injector rating (lbs/hr) by 3,600,000 (lbs fuel per ms) (B)
>
> A/B = pulsewidth at peak torque
>
> Example:
>
> 454ci *90 VE=408ci
> 408/1728=0.2364......
> 0.2364......*0.07651=0.01809........
> 0.01809...../8=0.00226......
> 0.00226..../12.5=0.0001809.....
> 0.0001809/2=0.0000904.....(A)
>
> 30lb/hr injector/3,600,000=0.000008333....(B)
>
> (A)/(B)= 10.85ms pulsewidth
>
> Paul Saltwick
>
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