Vacuum needed to properly run a fpr?

[ChuckDeez]

Ok, does anyone know who much vacuum it takes to make a fuel pressure regulator work properly? I'm seeing 12in Hg at idle and my fuel pressure dosen't change like is should when I remove the vac line. It's 38psi at idle, it does go up when driving to around 42psi. This is with the stock regulator, I tried an adjustable one with the same results, I'm also running a 255lph high pressure pump as I have a dry nitrous kit on the car.
Thanks for any help.
Chuck

 

[mustangfan1990]

Thats enough vaccum your fuel pressure at 42 is plenty I would say. Max fuel pressure is around that anyway....when you are driving your car at WOT there is no vaccumm. When I barely hit my gas to accelrate my vaccum goes to 0 so dont think your problem lies with your FPR. When you take the line off it should go to max fuel pressure. But to me your FP seems fine IDK though

 

[ChuckDeez]

Thanks for the response, the only reason I asked was because when the car was mostly stock the fuel pressure at idle was around 32psi and would go up to around 40psi when at WOT. I changed the cam and fuel pump at the same time and now the fuel pressure dosen't act like it used to. I'm just trying to figure out if it's the lack of vacuum or the high pressure pump that is responsible for the change in fuel pressure.
Thanks again,
Chuck