So I did the hutch mod while I had my tank out... U have the riff raff frx installed... My fuel pressure with the middle spring installed was 65 and 62under load.. After hutch mod my pressure runs 69 to 70 and 64 u den load... Is this expected?

 

Not unheard of. I think it has to do with the return line routing and extension under the fluid level, that or the use of fittings that restrict the flow in the return line.

Doesn't really have a negative effect so I wouldn't worry about it.

 

mine had similar numbers. put the lightest spring in and now running around 60, dipping to low 50's at wot

 

I ran into an issue with the hose clamp on the new fuel line connected to the tank. I double-clamped that and problem was solved. I use the lightest FRx spring as well: 60 PSI while running, no less than 55 PSI at WOT. This is with a new OEM pump and an inlet strainer, not an inlet filter.

 

So what is optimal fuel pressure for our truck? I could put the lighter spring in.. Would there be any benefit to the lower fuel pressure can the little higher number cause any issues?

 

Do not get below 46 psi (OEM factory spec number to run correctly).

 

High fuel pressure just works the pump harder, it does not improve performance. In fact, high FP and pouncing on the throttle makes a weird dynamic where the FP dips hard for a sec, until the pump has the opportunity to "ramp up" to the fuel demand. Lower pressure (regulator open more) makes a consistent higher flow through the pump, and WOT just diverts that flow (indirectly) from the regulator outlet to the heads.

 

ok so should i install the lower pressure spring or is it ok.

 

Completely up to you. The fuel pump is either on 100% or off 0%, so I don't really agree with the working it harder angle. Varying backpressure might theoretically put some additional strain on the pump, but it's all well within the spec of what the fixed GPH pump can handle.

If 60+ psi fuel pressure really caused a bunch of problems with the pump, do you think this is the first we would be hearing of it? Do you think Clay would be selling upgraded higher pressure springs? Do you think we would have mods dating back for years and years such as the BB mod designed to increase fuel pressure?

There's been several stories where fuel pressure over 70 psi starts to cause issues on some trucks but not others. But that mostly has to do with idle issues.