When they put the cummins 24v in a ford f650, the overflow valve is not threaded into the injection pump. It is threaded into the full return tee at the rear of the block. Does keeping the fuel return off the back of the head pressurized like that help performance?

 

Suppose to be at the VP44 output port...

 

In a Cummins yes, in a F650 it may not be. I haven't seen this set up, but am not saying it can't exist.

I can't see keeping residual pressure in the return side of the injectors will aid in any type of performance.