What duty cycle range gives the most accurate injection for an injector?
And how do I find out what fuel injector size I'll need for a given amount of HP?

 

Did you look at the Automotive Calculations on CamaroZ28.Com sticky at the top of the Engine Tech forum?

 

One guideline I've found to be helpful for sizing injectors is to multiply the flywheel HP X 0.07 to get the minimum acceptable injector size. Example:

500 flywheel HP x 0.07 = 35 #/HR

That is only for normally aspirated engines, and assumes a moderately efficient tune (0.476 #/HR/HP brake specific fuel consumption) and a maximum duty cycle of 85%. There is no problem going with a larger injector than you need, as long as you don't get ridiculous. The big problem is the ability of the PCM drivers to operate the large injectors at the small pulse width required for idle. The LT1 PCM doesn't seem to have any problems with injectors up to 42 #/HR with regard to idle quality.

 

I forget where I was reading it, but most injectors hit their max flow rate around 80-85% and some of them actually flow less as they approach 100%.