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Fuel flow is controlled by varying the pulse width or
duty cycle of the injectors. Pulse width is the time in milliseconds
that the injector is open, while duty cycle is the injector’s overall
percentage of open time. A 70 percent duty cycle means that the injector
is open 70 percent of the injector’s maximum cycling time.
Ultimately, to find the optimum injector size for a given application
you have to test it. You can map it out on a dyno, sizing the injector
based on observed maximum brake horsepower (BHP), and the brake specific
fuel consumption (BSFC) at the peak power. You can also use a wide band
oxygen sensor that tells you the air/fuel ratio at the load points
you’re tuning for.
The following formulas will get you close to the correct size
injector for wide throttle performance:
(BHP x BSFC) = Injector Size (Flow Rate)
# of Injectors x 0.8
The scaler 0.8 adjusts the calculated injector size to produce the fuel
necessary for peak power at 80 percent duty cycle. An accurate BHP
figure is critical for proper injector sizing, but not all dynamometers
have fuel flow hr. for normally aspirated engines.
For example, look at an engine with a known BSFC of 0.49 making 300
Applying the formula we derive:
300 X 0.49 = 45.9 lbs. /hr (required injector flow rate)
4 x 0.8
1) The STD injectors for a 2.2 Cavalier N/A is 17 lbs. So if you
want to figure the injector size for whatever HP you want to achieve
just plug in your figure.
Let’s take for example, you want 150 HP then the figures would look
something like this.
* (150) x .49 = 7.35 = 22.96 Injector Flow rate
4 x 0.8 = 3.2
For motors that want to make high HP like 175-225, just insert that
number above where the * () is located.
Some guys try to get more out of their injectors by adding more fuel
pressure to the existing injectors. This practice will significantly
reduce the injector’s life span by over working.
In cases of turbo's there is a complete new set of rules, we can help
you establish an injector size (usually 30lbs or over), and upgrade the
fuel pressure. Let us know what your project goals are.
2) For upgraded motors and all turbo's, we do have the ability to
adjust your ECU for tuning, rev limiter, and fan switch adjusting and
injector size. Again let us know your projects needs.
Call us anytime at (985) 956-7009,
and we can help you achieve your project goals!
CLICK HERE for
our Cavalier 2.2 Fuel Injectors!
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