Efi fuel return pipe

winkle · Post by **winkle** » Fri Aug 17, 2007 8:50 am

Im sure this question has been asked before, but is the fuel return pipe to the tank the same diameter as the supply from the pump

Im running a 3.9 hotwire system in a circuit racer so ive got nothing standard to refer to.

3.9 spaceframe toyota starlet.
Live dangerously, syphon fuel, smoke in bed, run with scissors!

chodjinn · Post by **chodjinn** » Fri Aug 17, 2007 9:56 am

Well the fuel return pipe on my 3.9 MGB is the same diameter as the supply; 8mm.

winkle · Post by **winkle** » Fri Aug 17, 2007 10:14 am

Thanks for that, youve put my mind at rest. I was sure it was but a couple of people put doubts in my head!

Ian Anderson · Post by **Ian Anderson** » Fri Aug 17, 2007 12:20 pm

The return pipe should be of such a size that it can flow the maximum capacity from the pump.

So if you are idling and the engine is not using much fuel then your return should be able to flow pretty much all the capacity of the pump.

Now say for example you run 8 mm to the rail and 4mm after the rail the decrease in capacity will cause an increase in fuel pressure and this will cause havoc with the settings. (OK this is a fairly extreme example but you get the ides)

By running the same diameters you should not have any problem.

Ian

winkle · Post by **winkle** » Fri Aug 17, 2007 1:14 pm

Thanks Ian I appreciate your advice also. Will run both supply and return in 8mm.