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Josh Able: puny fuel injectors
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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