Josh Able: puny fuel injectors

[mkii@nycap.rr.com (Josh Able)]

Billy1.8t (probably the fastest 1.8t) has 4 extra injectors wired up. :D


Josh Able

----- Original Message -----
From: "Brian McGarvey" <brianm@earendel.org>
To: "Jonas K." <jkarlsso@metabolex.com>
Cc: "scirocco list" <scirocco-l@scirocco.org>
Sent: Tuesday, June 11, 2002 1:56 PM
Subject: Re: Josh Able: puny fuel injectors


>
> Hmm..
> the engineer in me speaks up. Somebody noted the issue of resolution and
> FI in the same sentence. Why not use t-body injectors for idle and main
> injectors for off idle.
> brian.
> why just use one injector when 2 will do...
> brian
>
>  On Tue, 11 Jun 2002, Jonas K. wrote:
>
> > On 6/11/02 9:22 AM, "Josh Able" <mkii@nycap.rr.com> wrote:
> >
> > >
> > > 31 pound = 310cc
> > > running at about 75% duty cycle
> >
> > OK, good to know.
> >
> > > trust me Scott, other shops that sell full kits use these and produce
350ish
> > > hp.
> >
> > For those interested in this, here are the formula's lifted from Marren
Fuel
> > Injection's website <http://www.injector.com/fuelinjectors.htm>
> >
> > ------
> > Injector Flow Rate (lb/hr) =  (Engine HPx BSFC)/(Number of Injectors x
0.8)
> >
> >    For example, to calculate the individual injector size for a 650 HP V
> > using 8 injectors and assuming a BSFC of 0.5:
> >
> >  Injector Flow Rate (lb/hr)  = (650 x 0.5)/(8x0.8) = 50.78 lb/hr
> >
> > If you know an injector flow rate, you can solve the above equation for
a
> > rough estimate of fuel system capacity like this:
> >
> > Engine HP = (Injector Flow Rate x Number of Injectors x 0.8)/(BSFC)
> >
> >    For example, using the same estimated values from above:
> >
> >     Engine HP =   (50 x 8 x 0.8)/(0.5) = 640 HP
> > ----------
> >
> > These are universal formulas, it's related to how much energy is stored
in
> > the chemical bonds of the fuel, which is released as the fuel is turned
into
> > water, CO2, CO, and NOx.
> >
> > BSFC is Brake Specific Fuel Consumption. 0.5 is typical.
> > The 0.8 you see is for 80% duty cycle. We'll sub in 0.75 since your duty
> > cycle is 75%.
> >
> > The second formula then becomes:
> >
> > Engine HP = (31 x 4 x 0.75)/(0.5)  = 186
> >
> > This assumes fuel pressure of 3bar
> >
> > Josh, I'm not doubting your dyno charts. I just think that everything
> > doesn't add up (or multiply and divide either). If you really are
getting
> > 300whp from 4 31lb/hr injectors, then you've just become the hero of all
the
> > environmentalists and conservationists out there. You're generating 160%
of
> > the power from the same amount of fuel. People have been trying to do
that
> > for about 100 years. :-)
> >
> > Seriously, I'd really be interested in your setup (injector size,
pressure),
> > as I'm dropping a turbo into my Audi. 2.3l, 20v, k27/k26 hybrid turbo,
> > 36lb/hr injectors, 4bar. I'm aiming at 300Hp myself to keep it nice on
the
> > street. My own calculations indicate that with 5 injectors at 36lb each
this
> > is about right.
> >
> > Also, what's your idle like. I've heard that with big ole injectors,
> > resolution at idle gets poor, so it gets real rough below 1000rpm.
> >
> > Anywhoo,
> > My .02
> >
> > Jonas
> > 78 Scirocco 1.8
> > 85 Scirocco 2.0
> > 90 Coupe Quattro 20v
> >
> >
> >
> >
> >
> > > From: "Scott F. Williams" <sfwilliams@comcast.net>
> >
> > >
> > >>> nope, even 20v turbos pushing closer to 375hp use 310 many times,
> > > anything
> > >>> they tend to run to rich.
> > >>
> > >> My man, this is 100% *impossible*. Way more gasoline is needed to
make
> > > that
> > >> kind of power. This isn't even an engine capability discussion. We're
> > >> talking about the amount of chemical energy stored in a given volume
of
> > >> gasoline. There's only but so much in there! Like I said before,
there are
> > >> three ways to flow more fuel:
> > >>
> > >> a) increase the fuel pressure
> > >> In order to make 297hp at the wheels, you'd have to run a fuel
pressure of
> > >> 185psi. This is about 4x the stock amount. Not only would this burst
the
> > >> fuel lines, it would blow the fuel pressure regulator to bits,
destroy the
> > >> injectors immediately, and would completely overwhelm the engine
> > > management
> > >> system.
> > >>
> > >> b) leave the injectors on longer
> > >> The injectors can only flow their maximum rated amount of fuel. In
your
> > >> stated case that is 310cc/minute at full duty cycle. However, the ECU
> > > pulses
> > >> them on/off at anything less than full load. That is how you get a
> > > variable
> > >> amount of fuel delivery. Figure at idle they might be running at 5%
duty
> > >> cycle. Running them at maximum flow (non-pulsed)is 100% duty cycle.
> > > However,
> > >> the maximum safe duty cycle is 80%. Pushing the injectors beyond this
> > > point
> > >> for a prolonged period of time will destroy them.
> > >>
> > >> To make the point clear, in order to deliver enough fuel at a
*dangerous*
> > >> 100% duty cycle (at 50.75psi fuel pressure) you'd need to run 480cc
> > >> injectors! Those 310cc pee shooters would be overwhelmed at just
210hp! In
> > >> fact, with that math considered, it sounds like the 310cc are the
engine's
> > >> *stock* injectors.
> > >>
> > >> c) install bigger injectors
> > >> If you're following me so far, you'll understand why what you're
claiming
> > >> isn't feasible in the slightest.
> > >>
> > >>> hm..31 pound injectors do = 310cc right?
> > >>
> > >> Er... *no*. The conversion is actually 10.5:1. That is, 1lb/hour =
> > >> 10.5cc/min. So, if you've really got .31 pound injectors, then the
metric
> > >> flow rating is really 3.25cc. Now *that* really is far fetched! :^)
> > >>
> > >> Seriously, man. You need to go back to your builder and demand
accurate
> > >> information. Little injectors like that are simply incapable of
flowing
> > >> enough gas to produce the horsepower that they've sold you on. I
totally
> > >> believe that your engine can make that level of power. However, the
> > >> injectors aren't up to the task. You've either got erroneous flow
capacity
> > >> information or you're making a lot less power then you think.
> > >>
> > >> I'm not busting your balls, of course. These are the inflexible laws
of
> > >> physics and thermodynamics that we're playing with here!
> > >>
> > >> P.S. If you're injectors are grossly undersized, you will blow the
thing
> > > to
> > >> smithereens in short order. You *must* do the research to ensure that
> > > you've
> > >> got a safe combination. Do it in the name of science, paranoia, or
> > > whatever.
> > >> Just do it and do it right away.
> > >> --
> > >> Scott F. Williams
> > >> NJ Scirocco nut
> > >> '99 Subaru Impreza 2.5 RS
> > >> Mazda 323 GTX turbo "assaulted" vehicle
> > >> Golf GTI 16v "rollycar"
> > >> ClubVAC: "Roads found. Drivers wanted."
> > >>
> > >>
> > >>
> > >> _______________________________________________
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> > >>
> > >
> > >
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