[ZX3TUNR]

Found this on another site posted by Shmee. Very interesting..

Quote:ok, so you've upgraded your car with a bunch of aftermarket parts and want to get the most out of everything you have. one way to do this is to replace your stock injectortors with bigger ones for more reliable fueling.

Here is how to choose what suits you best:

Step #1
Determine your Hoursepower
You can figure out your hp by taking a few runs on the dyno, this is the best way to do itbut there are other ways. The Gtech Pro if set with your correct weight is fairly accurate or you can make a guesstimate based on the "Reported" hp gains from each aftermarket part(this is not a very accurate way of determining your hp but it will work if you make conservative gains for each part).

Step #2
Determine Approximate "BSFC"
Brake-specific fuel consumption(BSFC for short) is the amount of fuel consumed per unit of power produced. You can determine your exact BSFC through dyno testing or estimate this figure using the chart below.
Engine type............BSFC Using Gasoline
High Compression..............0.45(no-to-few mods) to 0.55(highly modified)
Super/Turbocharged............0.55(no-to-few mods) to 0.65(with modifactions)

Step #3
Determine Safe Duty Cycle
The duty cycle is the time the fuel injector is open verus the total time between firing events. The safe duty cycle is 0.80 for most OE Engines and 0.85 for modified and road racing engines.

Step #4
Calculate You Optimum Injector Size
With the info from steps 1-3 above you can now calculate your optimum fuel injector size for your car.

Max.HP x BSFC
--------------------------------- = Injector size in lbs/hr
number of injectors x duty cycle


We'll use a fairly well modified Focus with all the basic bolt ons which makes approximately 150fwhp for the following example:

150 x 0.48
------------ = 22.5lbs/hr
4 x 0.80

to convert your optimum injector size from lbs/hr to cc/min you can use this formula:

lbs/hr x 60
------------ = cc/min
6.177

Our Focus converts as follows:

22.5lbs/hr x 60
---------------- = 218.6cc/min
6.177

You should ALWAYS round up to the next highest size of injector so you have room to work with if you decide to add additional mods after you upgrade your injectors.

While it is not entirely needed to upgrade your injectors at 150hp in a Focus, it's still not a bad idea if you think you might be leaning out.

hope this helps some of you guys.