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I just added a fuel cell in my car and not sure on vent size. I’ve searched some and haven’t found a whole lot of info. Is a -6 vent enough or should I use -10?
 

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Ok thanks! I’ve got everything I need to do it in -6. Guess I should order the stuff in -8
 

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How big is you fuel pump? That will determine the size you need. I do agree, -8 should be plenty, but if you don't have a killer fuel pump, you can get by with the -6 you already have.
 

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T/S 368E
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.

If you already have a box full of -6 stuff, just do 2.
As mentioned, all of my cars are -8, very common even with a monster 500+ pump.


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unless you are making a shit ton of hp -6 is plenty. I made 800hp on e85 using the factory vent which was slightly smaller than -6.
 

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Discussion Starter #9
Car makes 1k at the wheels. Not sure on the pump size at the moment can’t remember but 120lb injectors at 80%
 

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Be safe run 2 -6. Pump size and style are what are important to know how much venting. Mechanical need a ton, in tank electric, not so much.
 

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I wouldn't put a loop in the vent line. If gas gets in there the loop will work as a trap and wont vent properly. I ran mine up high in the trunk and through the floor with a bulkhead fitting.

Exactly what I did in my no-box car, I didn't want to risk it being blocked.


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The vent only needs to be big enough to let air into the tank to make up for the amount of fuel the engine uses plus a very small amount for evaporation. The size of the fuel pump makes no difference. You are only trying to let enough air into the tank to make up for the fuel that leaves the tank and doesn’t return. A -6 is more than enough for this application.
 

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Methanol needs a bigger vent than gasoline


The vent only needs to be big enough to let air into the tank to make up for the amount of fuel the engine uses plus a very small amount for evaporation. The size of the fuel pump makes no difference. You are only trying to let enough air into the tank to make up for the fuel that leaves the tank and doesn’t return. A -6 is more than enough for this application.
 

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Discussion Starter #16
Cool. Thanks for all the replies believe I’m gonna do the 6 and ride on.
 

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-6 is plenty of vent size for just about any application. As was pointed out in a previous post, the function of the vent is to allow sufficient air into the tank/cell to compensate for the volume of fuel being pumped out.
 

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Be safe run 2 -6. Pump size and style are what are important to know how much venting. Mechanical need a ton, in tank electric, not so much.
I dont understand this. Its the quantity of flow out of the tank that matters. Why would the style of pump determine that on any given engine?
 

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I dont understand this. Its the quantity of flow out of the tank that matters. Why would the style of pump determine that on any given engine?
Belt driven mechanical pump needs to be gravity fed, known to cavitate when it has to try to pull fuel into it. Also fuel has to travel a few inches to feet to get to the pump itself. An in tank pump has a constant supply right at the inlet amd dont have a problem pulling fuel into it itself.

It's why a mechanical pump has 14, 20 or larger feed hose
 
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