What would happen if Install FPR with Stock FPR still attached?

I were not getting enough pressure with stock as fuel is returning running into my adjstable FPR would it not just always stay pressured at least were my adjustable would be set?

 

the pressure would always be the higher pressure setting between the two. i.e you would only be able to increase pressure with the adjustable, not lower it from stock

 

See this actually has me thinking, because if we're talking absolute pressure and not relative then yeah, adding an FPR would definitely make it run about at the higher of the two. BUT, what if both FPR's operate on relative pressure? The comparative pressure between the inlet and outlet of the FPR. If that were the case then with two 35psi FPR's there's basically 0psi* fp at the return line, then 35psi* between the last FPR and the first FPR, then 70psi* before the first FPR. This is, of course, assuming the pump can withstand/maintain that kind of backpressure.

*relative to atmospheric pressure for simplicity's sake, the math should work fine and it's easier to understand this way

 

if your fuel pressure is too low, it is likely a fuel pump voltage issue (assuming you have a properly sized fuel pump). An FPR is like a wastegate--if it is undersized, you will get spikes. Now that doesn't mean FPR's don't fail and result in lower pressure, but that's not too common on these cars. Usually you get a pressure drop from a fuel pump problem or a pressure spike due to a larger fuel pump on a stock FPR.

 

agreed

you really only need to upgrade your fpr if your pressure is too high.. if the pressure is too low, your fuel pump is not flowing enough. and it is not very healthy for your system to run more pressure than stock