Injector HP ratings:
Calculating injector size: the first thing you need to do is to project the max HP you think you will make.
Divide flow rating by .5 and multiply the result by the number of injectors. This uses a 100% duty cycle.
These ratings are for naturally aspirated engines.
Example:
19/.5 = 38, 38 x 8 = 304 HP
24/.5 = 48, 48 x 8 = 384 HP
30/.5 = 60, 60 x 8 = 480 HP
The preferred duty cycle is about 85% maximum, so for a safety factor multiply the final figure times .85.
304 HP x .85 = 258 HP
385 HP x .85 = 326 HP
480 HP x .85 = 408 HP
Remember that the above ratings are at 39 PSI. Increasing the pressure will effectively increase the flow rating. Example: a 19 lb injector will flow 24 lbs at 63 PSI, and a 24 lb injector will flow 30 lbs at 63 PSI.
See
Automotive Performance Software / Interactive JavaScripts Calculators to get the calculators used in these examples.
Here's the duty cycle explanation. Duty cycle is how much of the time the intake is open the injectors are turned on. The 85% figure means that for 85% of the time the intake valve is open, the injectors are spraying. The idea is that you want some percentage of the duty cycle left over so that you have some room to grow the process.
If you are at 100% and you need more fuel, all you can do is turn up the fuel pressure. That means the whole fuel curve from idle to WOT is affected. Maybe you are already too rich at idle, and turning up the fuel pressure makes it worse. If you had some injector duty cycle left to play with, a custom tune could use that where it is needed. That would not over richen the whole range from idle to WOT.
Diagram courtesy of Tmoss & Stang&2birds
Other fuel system components you'll need with bigger injectors
Remember that if your increase injector size, you need to increase fuel pump size too. If you don't the larger injectors will run out of fuel pressure. The minimum recommended fuel pump size would be a 155 LPH unit which is good for 440 naturally aspirated HP. You can go larger if you want to, the excess is returned to the tank.
If you choose larger injectors, you will need a matching calibrated MAF or a custom tune. I recommend PMAS MAFs. See
HOME - they are rebuilding their website as of 30-Sep-2010, so you may not find all the information you would like to have.
I would also recommend that you plan on installing a adjustable fuel pressure regulator with the new pump. It will help you tune the system. I recommend Kirban fuel pressure regulators. See
Kirban Performance
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring
Mustang FAQ - Wiring & Engine Info Everyone should bookmark this site.
Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif
Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif
Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif
Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg
HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif
TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif
Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif
