[Formulajones]

It depends on how far you are regulating it down, how big the pump is that is required to feed the HP you have etc...

If you are running a simple 500hp setup with a carb, and regulating it down to 6-7 psi, you can run a typical 255 LPH pump. In which case you can probably get away with a 3/8 return line. I still generally run a 1/2" return anyway because the cost is the same, and it leaves room to grow later. I tend to like running a bigger pump than required anyway to give some wiggle room that the formulas don't take into account like friction and G forces that affect fuel delivery. Plus most of the pump ratings are free flow anyway.

[FrankieT/A]

Originally Posted by Formulajones

It depends on how far you are regulating it down, how big the pump is that is required to feed the HP you have etc...

If you are running a simple 500hp setup with a carb, and regulating it down to 6-7 psi, you can run a typical 255 LPH pump. In which case you can probably get away with a 3/8 return line. I still generally run a 1/2" return anyway because the cost is the same, and it leaves room to grow later. I tend to like running a bigger pump than required anyway to give some wiggle room that the formulas don't take into account like friction and G forces that affect fuel delivery. Plus most of the pump ratings are free flow anyway.

I agree with a lot of what Jones is saying. But be careful, I put in a Walbro 340 LPH pump and that friggin' thing puts out 90 PSI of pressure dead headed. Lol