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are ls1 tanks pressurized?

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Old 05-02-2007, 10:02 AM   #1
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Default are ls1 tanks pressurized?

Im setting up a dyno with an ls engine and I am using a stock fuel pump/sender assy in a custom tank. I do not have the evap system hooked up so the center line coming out of the tank is just open to the atmosphere. There is some concern that the gas heating up and coming back into the tank will cause it to become pressurized. The building admin is concerned that this is a safety concern. I obviously cant vent this directly into the room either.

I know there are a number of people here running this same setup, including myself on my project truck, but how can I explain that this is an ok setup to run?
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Old 05-02-2007, 10:41 AM   #2
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An EVAP system prevents any 1970's or newer tank from becoming pressurized.

Before EVAP systems (ie, like on my 68 Camaro), fuel tanks became pressurized as fuel evaporated. The tank vent is located in the gas cap on my Camaro, and it has a 1-way valve so that air can come in but fumes can't escape. Venting gas fumes inside a garage is a bad thing. When I remove the gas cap to fill up, there is a big whoosh as the pressure is released.

Or that's how it would be if my crappy repro SS gas cap didn't leak.

So, you've got three options:
1) Run the EVAP system
2) Put a 1-way check valve on the vent line and let the tank pressurize
3) Cap off the vent line and switch to a vented gas cap
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Old 05-02-2007, 11:00 AM   #3
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I would think you could simply vent through a charcaol cannister. Anyone?

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Old 05-02-2007, 11:16 AM   #4
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I am just using my stock 71 Chevelle Charcoal can... with the EVAL line of the LS1 Manifold connected to the Can to pull vacuum.
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Old 05-02-2007, 11:55 AM   #5
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so if i run the center vent on the sender assy to a charcoal canister and then back up into the intake I should be good?

I always thought the center vent only allowed air to come into the tank and not out of but I guess that woulnt make any sense.

What kind of charcoal canister can I use that is easy to hook up?
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Old 05-02-2007, 12:32 PM   #6
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You can just about us any one you find.. I am just using my stock GM / Chevelle one, many have found the late model Mustangs, which are very small and can be hidden under or near the fuel tank a good choice.
Didn't your car/truck have one or just the EVAP pruge valve.
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Old 05-02-2007, 03:37 PM   #7
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Quote:
Originally Posted by jimmyp
so if i run the center vent on the sender assy to a charcoal canister and then back up into the intake I should be good?

What kind of charcoal canister can I use that is easy to hook up?
1. Yep.

2. The mid 80`s GM`s have an easy to hook up canister, only 2 lines, one to the tank and one to the purge valve. I don`t know if that tank would easily fit your mounting and space requirements. It was use on many models, El Camino, Monte Carlo, malibu, cutlass, caprice, pariesenne(sp?), regal, etc.
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Old 05-02-2007, 05:08 PM   #8
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Quote:
Originally Posted by jimmyp
so if i run the center vent on the sender assy to a charcoal canister and then back up into the intake I should be good?

I always thought the center vent only allowed air to come into the tank and not out of but I guess that woulnt make any sense.

What kind of charcoal canister can I use that is easy to hook up?
You will need some type of purge valve too. If there was no purge line connected, eventually the canister will become saturated with fuel vapor. If the purge line is connected to vacuum all the time, it'll pull a vacuum on the tank and your fuel pressure will drop.
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Old 05-11-2008, 05:36 PM   #9
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Quote:
Originally Posted by jimmyp View Post
Im setting up a dyno with an ls engine and I am using a stock fuel pump/sender assy in a custom tank. I do not have the evap system hooked up so the center line coming out of the tank is just open to the atmosphere. There is some concern that the gas heating up and coming back into the tank will cause it to become pressurized. The building admin is concerned that this is a safety concern. I obviously cant vent this directly into the room either.

I know there are a number of people here running this same setup, including myself on my project truck, but how can I explain that this is an ok setup to run?
Jimmy, Its been a while...How did everything work out? Hows the truck coming along?
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1990, 454, assembly, camaro, check, disconnect, evap, fuel, install, ls1, oneway, system, tank, vacuum, valve, vent, ventilation

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