fuel tank vent size

[421Altered]

What is the proper size for a fuel tank vent when running alky with mech injection and a 1/2 pump, with a -10 line to the pump from the tank?  The tank is 4 gallons and mounted about 4 feet in front of the engine.  Also at the hit, is it possible for the fuel to slosh back due to g forces and close the rollover vent, thereby not allowing the tank to vent?  The rollover valve is mounted on the top rear of the tank.  Thanks.

[Spud Miller]

 For that size pump, a single -6 sized (3/8") vent would be more than enough vent. Air comes in a hole much easier than fuel goes out, so the vent doesn't need to be equal to the outlet size or anything like that.

 G-forces and the rollover vent shouldn't be an issue...suction will open it when it needs to. That same fuel rushing back hard against the back of the tank actually creates a bit of positive pressure on the outlet. No problem.

 Spud

[dusterdave173]

One note
I see almost every car with a curly "pigtail" with many loops
One loop will do--when you have a lot of tight loops fuel can stay there and actually block the vent like a sink trap
We ran a copper stub with one loop of clear hose so you could see what was happening--it never failed
3/8ths worked perfect and with the clear soft hose you can shove a bolt in the hose during travel or storage to prevent alky from sucking in water
Just my two cents worth

[Curly1]

I agree -6 is large enough.

[421Altered]

Thanks to all that replied and the info from Spud.  That's what I'm looking for. Thanks again!

[racerken]

Dusterdave.  That is why I run my loups horazontal  rather than vertical .

[dreracecar]

Quick test is to have the tank outside filled with water and the outlet blocked off, pull the plug and the water should not surge as it leaves the outlet, if it gulps and surges something is wrong. 

[421Altered]

Thanks dreracecar!