Injector sizing

[James Ballenger]

	Injector sizing is based on the fuel demands of your engine.  The best
formula I have found to do this is (Hp*BSFC)/# cylinders = (Lb/hr)/Duty
cycle.  I think must use Hp to find the correct size of injector for your
car.  Hp is power = force per unit time.  You need to know, based on
horsepower, how much fuel your car can consumer per unit time.  You must
know this on a per unit time basis to be able to find a fuel pump and
injectors that can deliver the necessary amount of fuel in the prescribed
amount of time.

	Your maximum pulsewidth will occur at max VE (max tq).  BUT, max tq occurs
below max hp.  So even though you will need the most fuel at max VE, you
should also have a longer time to deliver this amount of fuel.  So your
engine example is correct, partially.  Yes the 350 ft-lbs engine will use
more fuel at the max VE point, but because it has less horsepower, we know
that this point occurs much lower in the rev range than the other engine and
it will have significantly more time to deliver the amount of fuel you need.
This is why you need to consider Hp for injector sizing and not tq.

	You will need VE/tq to find the actual pulsewidths.  I am currently looking
for a formula or a source to calculate my injector pulsewidth tables based
on a tq curve I have.

James Ballenger


>-----Original Message-----
>From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
>Behalf Of Tlsalt at aol.com
>Sent: Saturday, February 24, 2001 11:40 AM
>To: diy_efi at diy-efi.org
>Subject: Injector sizing
>
>
>Hello all,
>
>    I have a question about injector sizing.  Does anyone know
>of a torque
>based injector sizing formula ? All of the formulas I've seen
>use horsepower
>to determine injector size.  I am looking at a supercharged
>application and
>am a little puzzled about the torque output.  If maximum VE
>occurs at the
>torque peak, won't the highest fuel requirement be at peak
>torque?  I realize
>fuel consumption will be highest over time at higher rpm, but
>I'm interested
>in maximum pulsewidth.  For example, I have a 3.8 liter engine
>with 270cc
>injectors that has around 240 hp and 230 ft/lbs of torque.  I
>am looking at
>another 3.8 liter engine that is supercharged with 350 ft/lbs
>of torque and
>less horsepower ! (how do they do that ?)  Obviously it takes
>more fuel to
>make an additional 120 ft/lbs of torque.  Does the higher BSFC
>(0.55 lbs vs
>0.45lbs) in the formula enough for this difference?  Am I
>missing something?
>
>Paul
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