Hi everyone today i removed the fuel pipe from my coupe which runs from the bay to the tank. Having seen how small it is i would like to increase it for better flow to the carbi (suck through turbo a14, low pressure electric pump) Can any one advise on which size tube to use. I was thinking 3/8" or is it a waste of time considering the tank still has the standard fitting which i think is 1/4"

Fuel line fuel flow:

1/4" Tube id. .180" HP pressure= 165, HP suction 110
5/16 Tube id. .243" HP pressure= 300, HP suction 200
3/8 Tube id. .310" HP pressure= 500, HP suction 335
1/2 Tube id. .444" HP pressure= 1000,HP suction 675

Suction size is between tank and pump, pressure size is between pump and injectors/Carb.

Hope this helps.

I would recomend going to at least 5/16 from tank to pump. 1/4" to the carb should be ok. But if you are planing HP/engine upgrades down the track, It is fairly standard to use 1/2" from tank to pump and 3/8" to fuel rail on anything up to about 500HP.

The above chart, Give you an idea. If you are getting close to 165Hp, You should go bigger than 1/4" to the carb.

not a bad guide, but dependant on some variables

with a low pressure pump 1/4" should be fine

the increase in pipe size is requred when using high pressure pumps such as EFI pumps. Over the length of the pipe the pressure will drop significantly if the pipe is too small.

rough guide

standard fuel pump is approx 3-5psi
elec lift pumps are 4-6psi
holley black/blue pumps are 14-16psi (suit blow through carby turbo)
Efi pumps are 50-90psi

I experienced lean running in top after a sustained run through the gears in my old rally sedan. It was running a Facet lift style pump with 3/8" piping from pump to carbs. Ended up pulling the tank and getting a 3/8" outlet welded in, also found bigger fittings for the pump and boring them out as large as possible, this fixed it up.
If you are going to the effort of running a bigger line, go that little bit more and fix the lot up to make it optimal.

Thanks for the help guys. My car is not going to be a power house but it might be one day ha ha ha. I think ill increase the size of the fuel tube and tank fitting as well since im going to do it i might as well do it properly. Ill most likely go 5/16 and make a two piece tube so it can be removed easily if needed.