The limit of 39/42lb injectors on 05+ 4.0Ls

[Justin@VMP]

Most of the 4.0 guys have been using the blue pencil 39/42lb injectors because procharger and vortech supply them and they have the correct connector. They are slightly longer than stock so .25" rail spacers have to be used.

They are really 42s if you go by standard injector flow ratings.

I had rebecca's car on the dyno for some testing. I didn't realize it back in march because I was only running the car to 6000rpm, but today running it to 6200rpm I can definitely see a lean slope at the end of the pull. The injectors were maxed out at 395rwhp/15psi. Raising the fuel pressure to 45psi kept them from pegging, and suprisingly the fuel pump had no problem doing this since I upgraded the wiring in march and dropped the duty cycle by 10-12%.

The car will be getting GT500 52s when I tune it to run on E85. The 52s are a direct replacement, same cost as 39/42s, and stock length so no spacers are needed. At the same time I'll probably install a Ford GT pump to get the extra fuel flow needed for E85.