I am making a fuel return block and my current return barb fitting has a 3/16" ID. I am assuming that this is too large and I am planning on adding a fitting to the inside and just drilling the required hole size.
My old filter with a return line has a 1/16" hole for the vapor return and the psi held steady at 6psi at idle. Should I drill it at 1/16" or just let the return line have the 3/16" ID to keep the fuel moving?

Note: This is for an electric fuel pump.

Thanks

Fuel return block ? Do you have a regulator ? you should and it will only return what doesn't get used.

The pump is a street pump and it only puts out 7psi max.
I am pretty sure that I have read some threads of members making their own return blocks (T's) and I am wanting to know what size restriction works. So far I have found threads showing .060-.080" in size.
Thanks

i use a vapor separator with a mechanical pump and reduce the return orifice size to .035".

How did you decide on the .035?

Does anyone know the thread size of a Holley/QF main jet? Is it 1/4-32?

Thanks

With the NAPA vapor return/filter with the .060" return orifice gave me 6+psi at the carb. If I make the orifice smaller, would the pressure at the carb go up until the fuel pump is maxed out?
Thanks

yes, not sure how much tho

With no regulator, "rule of thumb" the orifice should be .050". Too big and fuel pressure drops. Too small, there is not enough re-circulation to keep things cool and free of vapor.

Good info, thanks!

I have modified my return line barb fitting for a plug. I will drill the plug with the appropriate hole size before I install it.
If I can find a 1/4-32 tap, I may tap down farther into the barb fitting for a jet. Then I can test different size holes to see if the fuel pressure changes.

Thanks again to everyone.

I am using a Holley Red pump. My fuel pressure at idle always shows 6+ (apx 6.2-6.5) at idle with the NAPA vapor/fuel filter that has a .060 return hole.

I have a .052" drill bit that I might start with. I have plenty of plugs to drill out if I can't find a tap.

Thanks

a constant flow pump will probably react differently than a pulse. if .060" is working good for you now then stick with it.

I decided to start a little smaller on the hole size with a .052" return hole. I now have a solid 6 3/4psi at idle!
Going from the .060" to the .052" moved the idle psi from 6 1/4 to 6 3/4! I am keeping it there since the pump is rated at 7psi.
Before I installed the return block, I was running water through it to clean it out before I installed it on the car. I was surprised how much fluid can come through such a small hole. This should still allow good circulation back to the tank.

Thanks allot for the replies!

Success! did you drill/tap the big end of the barb fitting for an NPT plug then drill/tap the NPT plug 1/4-32 for the holley jet?

I only tapped the barb fitting for the NPT plug, then drilled the plug to .052. I had trouble locating the 1/4-32 tap, so I just drilled the plug.
Thanks for your help.