Help Me with Injector Size

Don't forget that the BSFC will vary depending on how efficient the engine is. I'd use the following figures as a guide:

Bone stock 5.0: BSFC 0.51
Full basic bolt-on 5.0, stock H/C/I: BSFC 0.48
Mild H/C/I 5.0: BSFC 0.45
Higher HP H/C/I 5.0: BSFC 0.42

Using the 85% maximum recommended duty cycle and stock 39psi fuel pressure:

19lb injectors are good for up to 270hp (full basic bolt-on 5.0).
24lb injectors are good for up to 390hp (higher HP H/C/I 5.0).

You could increase the fuel pressure with an adjustable regulator to raise the HP threshold but there's a limit to how far you can go without risking the injectors sticking open.
e.g. Ford Racing 340hp crate combo (GT40X heads, E303 cam, Cobra intake). Assuming a BSFC of 0.45 (Mild H/C/I), stock 19lb injectors would be at 100% duty cycle at stock fuel pressure. Even if you raise the fuel pressure to 50psi, the injector duty cycle would still be too high at 88%. If you use 24lb injectors at stock fuel pressure, the duty cycle will be a comfortable 80%.

If you're likely to err with the injector size, it's better to err on them being a little too big rather than too small. As long as the MAF is calibrated for the correct injector size and the O2 sensors are functioning properly, the engine computer's adaptive learning memory will ensure that the A/F mixture is close to optimum under all conditions.

Just tell us what your engine setup is and we will tell you what to use.
No reason to over complicate something so simple

Lifted94XLT said:

Sounds good, I'm slow when it comes to calculations::
Stock bore 302, Factory Crank and rods with Forged Aluminum Pistons (factory dish), Ported E6 heads, X303, 1.6 alum roller rockers, Gt40 intake, 70mm TB, bigger MAF (haven't bought yet obvisouly), and I'll be running a wet kit.... I'm assuming somewhere close to 100shot. I also have an Aeromotive Adj Fuel Press Reg so I can play with my pressure. I had it set to 42psi before motor went down for rebuild.... I think I've got everything in there.
Thanks for the help guys.
--Ryan

Click to expand...

You'll probably want 24 or 30lb/hr injectors for that build.

Keep in mind that a "wet" nitrous kit supplies its own fuel, so the engine's injector sizing doesn't need to be influenced by how much nitrous is added.

I don't know what your plans are for a fuel pump, but you're going to need something in the 190LPH range (but going bigger doesn't hurt). Fuel pump sizing IS influenced by the added nitrous system.

Assuming you have a headers-back exhaust, your 302 will be putting out roughly 320-325 flywheel HP (all motor) so you'll need 24lb injectors.