Re: Answers
The flow is rated in pounds-per-hour. The Brake Specific Fuel Consumption (BSFC) is simply how many pounds of fuel it takes to make 1 hp for 1 hour. BSFC will be about 0.45 for most street injection set ups. The formula for pounds of fuel per hour is:
BSFC × Peak HP = lbs/hr
The computer controls the duty cycle. If you run too large of an injector you're simply wasting your money; the computer will keep it closed until fuel is needed. On the other hand, if you run an injector that is too small, the computer will be cycling it open much more often to try and meet the demand for more fuel, which of course, the injector can't deliver.
Injectors will work best if they don't exceed more than 85 duty cycle. An injector that flows 26.5 lbs/hr will be at an 85% duty cycle when flowing 22.5 lbs/hr, but you may not find an injector that flows exactly what you need. The formula for injector sizing is:
lbs/hr = (BHP × BSFC) ÷ (No. of Injectors × DC)
Where:
BHP = Peak Brake Horsepower
BSFC = Brake Specific Fuel Consumption
DC = Injector Duty Cycle
You can figure how much hp your injectors can support with the following formula:
HP = (lbs/hr × No. of injectors × DC) ÷ BSFC
Using a 0.45 BSFC is good for normally aspirated engines, but if blower, turbo, or dry nitrous system is being used, a 0.5 BSFC is better.
If you are using 1 injector per cylinder in a normally aspirated engine, you can used the following formula to estimate the size of the injector by air flow:
Injector size = (CFM × 0.44298) ÷ (No. of cylinders)
And just for the heck of it: 
There are two basic types of injectors; saturated (high impedance), and peak and hold (low impedance).
Saturated injectors are more common and draw less amperage form the ECU. Saturated injectors also create less heat because the have less amperage. A saturated injector will have an impedance of about 12 ohms, this means that at 12 volts it take 1 amp to hold the injector open. Peak and hold injectors will have an impedance closer to 2 ohms and draw about 6 amps. Most ECM's cannot handle the amperage and using peak and hold injectors will harm the them. If you desire peak and hold injectors a separate aftermarket injector controller or aftermarket ECM may be required. Peak and hold injectors use high current to open the injector very quickly and precisely, then they draw less to hold the injector open. For high horsepower and flow rates, the peak and hold injectors are much more precise, but they are more venerable because of the heat they make. If it is a street engine that will be daily driven, saturated injectors are more reliable for long term use. Peak and hold are better for high horse power and competition use.
_ken
