Josh Able: puny fuel injectors

[brianm@earendel.org (Brian McGarvey)]

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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