Originally Posted by JustinC,May 1 2009, 05:59 AM

Hey guys,

I was wondering if there is a limit to the stock FPR. I know a lot of people go to a rising rate FPR.

I think the stock is rising rate, however I know it is not adjustable, just wondering at what boost level you should swap from the stock to an aftermarket one. I will be using KPRO.

Thanks

Originally Posted by suprmonky73,May 1 2009, 09:24 AM

sorry for the off topic but is your avatar from bonkers?

Originally Posted by siadam,May 1 2009, 09:21 AM

Our fpr's are rising rate. They are 1:1 I believe. I just made 500whp on the stock rail/fpr. Unless you need to run crazy fuel pressures, stock is fine imo.

I'd venture a guess than anything below 550whp-600whp is fine.

Originally Posted by Sellout,May 1 2009, 08:05 PM

A 1:1 pressure regulator isn't a rising rate regulator. It raises the fuel pressure 1 psi for a 1 psi increase in manifold pressure, which makes the ΔP across the injector the same regardless of manifold pressure. With 6psi boost and 43psi base pressure (set by removing the vacuum source from the FPR), the stock regulator would give you 49psi for a ΔP across the injector of 43psi.

A rising rate pressure regulator would raise the fuel pressure by something more than 1 psi for each increase of 1 psi in manifold pressure. If you're raising fuel pressure by 3 psi per pound of boost, for example, a 43 psi base pressure (set by removing the vacuum source from the FPR) would give you 61psi of fuel pressure at 6psi boost, which gives you a ΔP across the injector of 55psi.

You should only use a rising rate FPR for boost enrichment when you're not using a better method of controlling fuel. If you're running an AEM EMS, or a K-pro setup, you don't want a rising rate regulator, and the stock one should be fine all the way up until you're running a fuel pump so large that the stock regulator can't return enough fuel to keep the fuel pressure where you want it across the RPM range.