I have a 2006 GT w/Saleen SuperShaker. I have a 3.4 pulley with 39# injectors & GT500 fuel pump. I want to upgrade to 3.2 or 3.0 puley in the future. Do I need to increase injectors to 60# or will the 39# injectors be ok?

 

I have a set of roush p-51 injectors for sale they 52# injectors, I can let them go for 300 shipped. PM me if you are interested.

 

That's really a question of how much power you're going to be making. Because a specific sized injector will support x amount of power, you can calculate what you need based on your power output.

Other things to keep in mind is that you don't want your pump or your injectors running at 100% duty cycle. In fact for the injectors I'd want to stay somewhere in the 80% range.

Lets say you want to support 550 hp at the crank...or around 500 at the wheels.

To achieve that number with 8 injectors will require 52.6 lb/hr injectors to achieve 85% duty cycle. This is with the assumption of a higher brake specific fuel consumption due to being a force fed engine.

Conversely, with your 39lb/hr injectors you can support just over 400hp at 85% duty cycle. If you're much over that power output with your current injectors, you may or may not be on borrowed time, as you're eating into your safety margins for durability and repeatability.

here's a calculator you can use to determine what size injectors you need for your application.

http://www.z31.com/software/injector.pl

I hope that helps.