Fuel tank vent size

[PatricksDad]

The journey continues on my friend's '70 Chevelle. The fuel system is largely in place, save electrics (more on that later).

We've welded in a Moroso sump, and are using an Aeromotive SS 11213, deadheaded at a Jegs billet adjustable regulator, all feeding a Quickfuel Dominator.

Do I need to upgrade or replace the fuel tank venting system? I'm suspicious of the two lines that I can see coming out of the top of the tank, but since I have no idea how the tank was originally plumbed or vented, I'm looking for advice on using the stock setup or fabbing something custom.

[Barry Donovan]

deadhead is natural..
if you play with vent canisters, there shoud be a line going to it.

else a gentle suck at air plenum area is a good one, but not too much.
they do make vacuum only caps for 70s onward, vent cans..out all those hoses..those are the only ones I have kept.
one could make a lesser pressure fuel injection type setp with a return (my favorite to date with a carb)

[Scott Liggett]

Most of the GM cars of that era had a looped vent tube that went up through the trunk floor above the rear axle then made a 180* turn and back through the floor. I think the ones on my two cars are 5/16".

[PatricksDad]

Thanks, guys.

Is there a specific, or universal, check valve-thingy that I can put on the vent to keep crud out of the system?

[CDMBill]

I think the better idea would be a small inline type filter as the vent line has to allow air movement each way.

On another note while chasing a fuel pressure datalog issue I sopke to Aermotive about it and was told the vent line should be the next size down from the pump inlet line size on my return style set-up. That meant a #8 on my set-up. We didn't discuss dead head requirements. The fitting on my stock style Ford gas tank uses a 5/16's line but the tank fitting it attaches to turns out to have only a .040 pasaage in it. So I was asking my system to pull 43.5 psi and 1000 HP worth of fule against a .040 opening. Interestingly, I added a lst minute #8 vent tube before Drag Week and saw no difference in the log of the cars perfomance. But I did get a lot of gas fumes in the drivers compartment when the tank was full and the car wasn't moving. More work left to do.

[PatricksDad]

I think the better idea would be a small inline type filter as the vent line has to allow air movement each way.

On another note while chasing a fuel pressure datalog issue I sopke to Aermotive about it and was told the vent line should be the next size down from the pump inlet line size on my return style set-up. That meant a #8 on my set-up. We didn't discuss dead head requirements. The fitting on my stock style Ford gas tank uses a 5/16's line but the tank fitting it attaches to turns out to have only a .040 pasaage in it. So I was asking my system to pull 43.5 psi and 1000 HP worth of fule against a .040 opening. Interestingly, I added a lst minute #8 vent tube before Drag Week and saw no difference in the log of the cars perfomance. But I did get a lot of gas fumes in the drivers compartment when the tank was full and the car wasn't moving. More work left to do.

Thanks, Bill. We're not pushing your HP level yet, but we'll be sneaking up on it before too long. Probably worth it to just drop the tank again and plumb something proper.

[Deaf Bob]

For demo derby, we use 6 gallon boat tanks with a length of hose coiled in about a 6 inch loop.
Nothing gets in.. If the car should roll on it's top.. It will not pour out the vent.. Should gas get in the hose, the pump will suck it back into the tank..

[yellomalibu]

I think the 70 is considerably different than the 68 - but I just put a new replacement tank in my car. The 68 has a 1/2" and a 1/4" vent side by side on the forward top Right part of the tank. About 8" of each hose go up and clip to the axle well... That's all it had originally. I'm pretty sure the vents in the tank have a filter or check valve in them.

- but I have heard of people using a cheap plastic fuel filter in the end of a vent line to keep crud out.

[MR P-BODY]

The vent line will have a roll over valve to close
it off in case of roll over... a 1/4" vent is plenty...
a roll over valve can be bought from Summit

http://www.summitracing.com/parts/ABT-TF210/

make sure you install it vertically

[PatricksDad]

The vent line will have a roll over valve to close
it off in case of roll over... a 1/4" vent is plenty...
a roll over valve can be bought from Summit

http://www.summitracing.com/parts/ABT-TF210/

make sure you install it vertically

Excellent. Just what I was looking for, and I don't have to drop the tank to install it.

[MR P-BODY]

Excellent. Just what I was looking for, and I don't have to drop the tank to install it.

I know of some that put that valve on the end of a filter... I'm trying
to find a small charcoal filter then have that on the end... I havent
found a small charcoal filter yet

[SuperBuickGuy]

if the tank is like a 70 Buick. there's two vent holes in the top, passenger side, front corner of the tank - stock they have two hoses that run into a check valve. I had a lot of trouble keeping them from leaking, then also causing a great amount of vapor smells because vents into a closed area (the space above the axle). My solution was new hoses to the vent, then a hose from the vent to the wheel well....