Cutting gas tank, doing side exhaust, adding rear diffuser.

Originally Posted by phunk

The smaller line is just an air vent so that when you are filling the tank, trapped air doesnt make the pump stop short of full.

It sounds like you are saying you entirely eliminated the EVAP and breather system from the tank. This will create some side effects you need to address where the fuel tank can generate pressure when the fuel heats up or create vacuum when the engine has been running and the fuel level is going down. You need to have a way for the fuel tank to breath... OEM cars vent to the intake manifold so the car doesnt always smell like fuel vapor and of course evaporative emissions. Consider how much area a couple gallons of liquid displaces: then imagine how much vacuum will be inside a sealed tank to remove that volume of liquid without allowing air to replace it.




If you want to do something with that connection that would be really clever, clamp on a few inches of 5/16" gates submersible hose, thus creating a new (and stubby) jet pump inlet hose. Adjust its length to reach about 1/4" from the floor of the tank. This will put that jet pump to use as a canister filler, helping to fill that little bucket with fresh fuel from outside. The little black piece on the bottom of the canister is the exact same thing already doing that, this addition will double up on canister filling.

Originally Posted by synolimit

I pressure tested that small line with the gas cap on, i was wrong. At a few psi the gas cap has a release valve open so its not a direct atmos vent like i thought. The hole i saw under the gas cap just drains onto the tire. So when the tank does build pressure the air can escape. As for a vaccum im gonna guess thats a one way only valve. Not sure how i can test that or if it'll be a problem. I always thought the main issue was pressure and all tanks need a release which i tested and it has. My guy did say we could weld on a new nipple and run another line up by the filler neck for even more pressure release. He said that'd make him feel more comfortable. Again as for the vaccum i dont know. Maybe on the new line run we can install a 2 way valve with a low pressure open/close.

I see what youre saying about the 5/16th hose. I could even Tee it and make like a sideways E for 3 pickups and more volume.