Contour Enthusiasts Group Archives Forums Modifications Zetec Performance Injector Sizes

The "(injectors size*number of injectors)/0.55=Crank Horsepower" is a very conservative formula that is usually used for forced induction applications. 0.55 BSFC is rather high for a naturally aspirated 16 valve motor. For a naturally aspirated Zetec motor, You shold be using (Horsepower*BSFC)/(Number of Injectors*Max Duty Cycle) = lb/hr needed.

Ford BSFC you can use a number in the range of 0.40 to 0/45.

So, if you have 170 HP at the flywheel and use a 0.45 BSFC, have 4 injectors and want 85% max duty cycle, the result would be:
(170*0.45)/(4*0.85) = 22.5 lb/hr.

If you can't get them in the size you need, you can round up. There are some injector manufacturers that sell 23 lb/hr and 24 lb/hr injectors.