So I finally got around to upgrading my fuel system for my LS swap due to needing a walbro 255 and having the fuel pressure rock up to 70 psi at idle. Ended up doing a Vette filter/regulator and when I removed the NB regulator I found a restriction orifice......a very small restriction orifice




Has anyone else seen this? Thoughts on its purpose? I'm guessing it's to smooth out the regulator function, makes me wonder if simply removing the orifice would have made the stock fuel system support 400whp fine, I had no pressure drop on the top end.

 

I’m certain my 99 did not have one of those in it. The effect would be to raise the pressure at the rail during idle, which makes no sense. I say that because at idle is when the flow rate through the regulator is greatest.

DNM

 

Right? It's very odd. I've had others confirm they had the same issue and others claim they didn't. This car was a california emissions vehicle at one point, wonder if that's a thing for those

 

Could it have something to do with how the unused fuel is returned to the tank? The nb returnless system does have a bypass return after the filter, and back to tank.

 

This is how a return less system works, it's not really return less, it's just a short circuit with a single line to the front of the car. The orifice is inline before the regulator so it'll cap flow and generally slow down the reactions of the regulator