When do you know you need one of these things? or how much horsepower before you drain your rail pressure? just wondering because i have heard people say different things.

 

FASS or GDP recomended around 475, and cp3 modifications are a toss up from truck to truck and setup to setup with programer/box stack and injectors one will be needed.

 

I would say less than that on some trucks, I was draining the rail and pulling lp psi down to 0 with the original Smarty on SW7(dynoed 407hp)

 

I noticed my truck would stop pulling with Crazy Larry on WOT runs in 5th and6th gear on the stock lift pump. If you do upgrade don't go too small like I did. As the mods kept getting done I have out grown my Fass 95/95 and have had to purchase a 150/150. Now I have a spare laying around I dont need