Fuel pressure / Flow rate formula

[Barry E. King]

fuel required per cylinder (lbs/hr) = (HP x BSFC) / (# injectors x IDC)

Assuming a normally aspirated engine, you'll expect to see roughly 0.5 lbs
of fuel per hour.  Use 0.6 for a forced induction application.

Target 80% IDC (injector duty cycle) so that the selected injector is not
running maxed out.

fuel/cyl = (400 HP x 0.5 lbs/hr/HP) / (8 cyl * 0.80)
         = 200 lbs/hr / 6.4 cyl
         = 31.25 lbs/hr/cyl

So, each injector needs to support a flow rate of at least 31.25 lbs/hr.
You can convert lbs/hr to cc/min by multiplying by a factor of 10.5  The
above example yields 328 cc/min.  Note that the above approach builds in a
safety margin.   It is generally considered not cool to run injectors much
past 80% duty cycle for extended periods of time.

I just checked:  RC's website also has this same formula on their site.

There are other more accurate ways to determine fuel requirements but this
formula seems to be very close.


Regards,

Barry

> -----Original Message-----
> From: owner-diy_efi at efi332.eng.ohio-state.edu
> [mailto:owner-diy_efi at efi332.eng.ohio-state.edu]On Behalf Of
> jdzura at csc.com
> Sent: Friday, November 13, 1998 7:01 AM
> To: diy_efi at efi332.eng.ohio-state.edu
> Subject: Re: Fuel pressure / Flow rate formula
>
>
>
>
> >You need to know HP of your app etc, then figure out max Lbs/hr fuel you
> >need to support it, and divide by number of injectors.  Once you have
> that,
> >use the next larger size to give you some room for "growth".
>
> Can you provide an example of the math? Say for a 400 HP V8
>
>
>
> Thanks
>
>
>