Fuel Hard Line size guidance?

GR124 · Postby **GR124** » Wed Sep 13, 2017 10:15 am

Still plugging away building my locost racer. To give a run down the engine is standard BP4W and will be run like that for now. However may upgrade to turbo (dreaming). I what to future proof the fuel system. Not sure if this comes into the equation but I have a Bosch 044 external pump.

The hard tube exiting and entering the standard fuel tank pump assembly is 8mm OD.

* Do I run 9.5mm (3/8) for both feed and return lines?

Postby **NitroDann** » Wed Sep 13, 2017 3:48 pm

That will be plenty for any project you have which is MX5 based which is not a competition drag car.

GR124 · Postby **GR124** » Wed Sep 13, 2017 5:35 pm

NitroDann wrote:That will be plenty for any project you have which is MX5 based which is not a competition drag car.

Dan, will 3/8 return be ok? no dramas with pressure loss?

Postby **NitroDann** » Wed Sep 13, 2017 6:27 pm

Im not sure what you mean by pressure loss on the return.

Explain?

GR124 · Postby **GR124** » Wed Sep 13, 2017 8:29 pm

NitroDann wrote:Im not sure what you mean by pressure loss on the return.

Explain?

Hi Dan
Excuse my lack of understanding, I'm learning fast,
I've done some more research and found that there is a fuel pressure regulator on the engine end of the fuel return line.
So I guess this FPR regulates the fuel pressure at the rail so the return line after the FPR can be as big as you like (in theory) ?
True????

Magpie · Postby **Magpie** » Wed Sep 13, 2017 9:03 pm

You want the hose size to match the orifice size of the FPR. You do not want to heat the fuel returning to the tank. You could consider going returnless as this removes fuel being returned to the tank.

GR124 · Postby **GR124** » Wed Sep 13, 2017 11:44 pm

Magpie wrote:You want the hose size to match the orifice size of the FPR. You do not want to heat the fuel returning to the tank. You could consider going returnless as this removes fuel being returned to the tank.

Thanks for your reply Magpie.
If been doing some WWW reading and the returnless seems a little daunting right at this time. I wanted to keep things simple, so for now (I think) the best rout for me is to keep the engine and fuel system standard with a return line.

I understand the returnless setup, its the regulator that has me a little confused. Do you require an electronic adjustable reg for returnless? I ask this because the standard FPR is operated by a vacuum hose.

Magpie · Postby **Magpie** » Thu Sep 14, 2017 8:24 am

the vacumn line on the FPR is for rising rate, that is increasing the fuel pressure as boost increases. Not needed in a NA car... The only thing I have noticed since swapping from a return system is the FP is a little less stable than it was in the past. This could be fixed by putting a fuel damper on, but I have not got around to that yet.

The fuel pressure rate is set and forget, unless the FPR fails.

A returnless system is where the FPR is installed, that is BEFORE the fuel rail not after.