Injector Rail

[tpepmeie]

Originally Posted by XfireZ51

Todd,
For purposes of comparison, aren't the Bosch injectors rated at 43.5?

It depends on who's quoting them. Most aftermarket resellers will use 43.5, because it is more standard. However, if you use Bosch-made Ford Motorsports injectors, they are typically rated at 39.15 psi. For example, the red Bosch 30-lbers I had in the 427 were Ford Motorsports injectors rated at 30lbs @ 39.15 psi. Ford provides calibration data which had the characterizations at all different pressures (they flow ~35 lbs/hr at our rail pressure.) The conversion from Ford characterization to GM tables is quite involved, but can be done.

Originally Posted by XfireZ51

Using a 50.8psi fuel pressure brings flow for the RCs to 21.5.
Not sure that the calibration value is at a 50.8psi. You might be able to shed more light on that.

I wouldn't speculate on what or why the GM calibration uses that 22.7 flow rate--I've always wondered that myself. I'm sure there is a reason. However, to accurately meter the fuel delivery, that variable needs to reflect the operating conditions of the injector. There is no other calculation in the program which converts that data value to the actual rail pressure. The regulator is designed to deliver a constant 3.5 bar (50.8 psi) pressure difference between the manifold and the injector feed. It's the flow rate under those conditions which dictate how much mass of fuel is delivered for a given pulse width.

Years ago, I had some lightly used stock injectors tested. They flowed 20.1 lbs/hr @ 43.5psi, which is 21.7 lbs/hr @ 50.8psi. Still short of the factory calibration value (22.78). It is possible that the flow v. pressure is not perfectly linear for the multecs, but who knows.