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

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.

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phunk

Better yet, forget the gates submersible hose, since you have the actual in-tank hose with its QD fitting already cut out of the tank, just cut that Nylon hose real short so it lays on the floor... or actually, cut it to a length where you can route it to somewhere else in the tank to act as a remote transfer pickup. I dont know, maybe all the way in the back of the tank to promote pickup when accelerating out of a turn at full throttle. Fuel consumption is obviously the highest at full throttle so somewhere towards the back would make the most sense.

This is a jet pump, so its not a real fuel pump pickup, its just a solid state transfer device that is delivering whatever it picks up to the inside of your fuel canister where your actual fuel pump pickup can get it.

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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.

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phunk

Sounds like you found a high pressure blow-off in the cap, probably some sort of safety feature, I am not sure I would rely on it as a constant duty device.

The hole that drains by the tire is not a part of the fuel system and can be ignored... this is just to drip out water or fuel that has pooled up outside the gas cap. There is another hole connecting the small port on the rear center of the gas tank to the filler neck tube just inward of the cap. This is a vent that only applies when filling the tank to allow air to escape while fuel pours in. Any time the gas cap is installed, this vent tube is irrelevant.

Sometimes high HP cars will starve fuel when the engine consumes fuel faster than the tank ventilation can alleviate the vacuum. This burdens the fuel pump and will reduce its output. Tank vacuum can create significant problems, so its something you want to make sure to address with priority.

If you add additional legs to the jet pump pick-up, you will defeat the functionality of it any time all the legs are not submerged.

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phunk

To be entirely honest, If I were in your shoes, I would just weld back in the panel with the stock fuel ventilation system... it is quite effective and Plug-and-Play with your car! Rather then invest a ton of time into reinventing something that is less than OEM quality, you can just put it back in.

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synolimit

Gotcha, i can do that. Even zip tie it to the rear baffle pointed down at the floor like a 1/4" up on more of the inside tank for though fast right handers.

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synolimit

So what would i do about the 1/2" nipple that was going to the evap can? If all that oem stuff is left in the tank whats going on the other side of the tank? Run a hose somewhere with a filter installed?

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phunk

Make sure to use 100% Nylon zip ties!

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phunk

Well you would have to put the evap canister back in there and hook it all back up as it was! Your other option is to make your own fuel tank vent and route it upward somewhere maybe by the filler neck and put a rollover valve on it so it doesnt dump fuel if the car finds itself upside down.

Be warned though - cars with open ventilation fuel tanks stink like fuel vapor! I have a very sensitive nose and it would annoy me personally, but im sure plenty of people dont mind.

Over the years I have seen plenty of people just drill a big hole in the gas cap for ventilation after removing all the OEM stuff. The downside here is there is no rollover protection. You may want to check rule books to make sure this wouldnt disqualify the car should it receive a detailed tech exam.

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phunk

Rummaging the service manual I see that the gas cap does indeed also have a vacuum relief function.

Go ahead and suck on your gas cap to see if it flows well enough that you can just ignore everything I have been talking about! Or if its just a like a final relief intended to open before the gas tank collapses.

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phunk

Here is the summary from the service manual.

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synolimit

awesome news. when i get home I'm gonna hook up a line so i can breath in and out and see if the gas cap will open and close. I know i can only do about 2psi so that should be a pretty good test.

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synolimit

Ok bad news, i cant open the gas cap with lung pressure so im going to have to find out how little it does take, because its more than 2psi.

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phunk

What about the vacuum test? Gotta figure out if your ventilation needs to be 1 way or 2 way.

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synolimit

Ill turn the air compressor down to like 5psi and go up from there and i can hook the vacuum up to it and see if it'll pull it open.

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