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fuel tank vent size

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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!

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