I don't know what size injectors are in my engine and was wondering if anyone knows what they are . I also have a set from Ford Racing and don't know what size they are, here is a couple of pic's of them..
Revised 20-May-2011 to add MAF and custom tune requirements for use with larger injectors
Injector HP ratings: 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 at the flywheel.
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.
19/.5 = 38, 38 x 8 = 304 HP x .85 = 258 HP
24/.5 = 48, 48 x 8 = 384 HP x .85 = 326 HP
30/.5 = 60, 60 x 8 = 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.
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.
With larger than stock injectors or higher that stock fuel pressure, you will need an aftermarket MAF that matches the injector size. The MAF ’lies” to the computer to get a fuel delivery schedule that meets the engine’s needs and isn’t too rich or too lean. The best strategy is an aftermarket MAF and a custom tune to insure the best air/fuel ratio over all the RPM range.
Don't forget to increase the fuel pump size with you increase injector size or significantly increase the fuel pressure
Diagram courtesy of Tmoss & Stang&2birds
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