MSefi.com read only forum (Jan.15,2018)

Hello,

I want to convert my small block chevy to FI. Any recommendations on the fuel supply and return line size ? The engines output would be somewhere near 500 hp.

Thanks

Yves

I haven't seen anything bigger than 3/8" If you are worried about pressure and gph, the fuel pump should be able to pick up the slack as far as pumping enough gas to your engine. Fluid mechanics says that you'll get the volume that you need...just make sure you have a pump that is powerful enough to do it. You can use a 3/8" return line as well if you want. I run a 5/16" return only because that's what was on the car and it was already in place as it was the original supply line.

Hmmm...could this be why my pump sounds louder during idle? I don't hear it too much during drive, maybe I should swap my 5/16" for a 3/8" perhaps....

usagoal wrote:Hmmm...could this be why my pump sounds louder during idle? I don't hear it too much during drive, maybe I should swap my 5/16" for a 3/8" perhaps....

If you can put a tap on the return line at the rail right after the regulator, and measure the pressure at idle, you'll be able to tell right away... Probably shouldn't be more than a couple psi. Hmm, could be the regulator too, if you have a big pump it might not be keeping up at idle?

I do actually have a threaded port on the fuel rail (after the regulator) to check fuel pressure. It's 35lbs at idle. Can't check during acceleration because the gauge won't reach the window. Goes up a little when I rev it though (it was late when I checked it, can't wake the neigbors). I can hear the pump change it's pitch during accel, decel, and especially coming to a stop it gets louder. Do you think it's working harder to push fuel through the smaller return line? Similar to a vacuum cleaner when you block off/restrict it's suction...it gets loud. Just my opinion. Just for info: I did check out the pump's specs before ordering. It should be enough for my engine.

I mean on the other side of the regulator, where the pressure should be zero, but maybe it's not...

And you can test the line pressure at WOT by just shutting off the engine, that puts the regulator port at ambient and hence the regulator thinks your running at 100 kPa.

Eric

Well mine is a C3 vette, so where in the same boat.

I would have expected that a return line would not have that much pressure since it has an open end in the tank...maybe i'm missing something.

I was planning on using an in line pump. Have not decided on the pump. Thanks to mention i should have 255 ltr/h