70NE's custom EFI conversion writeup - Part 2

[68converted]

The main concern is air in the fuel lines. We need a way of getting as much of this air out as possible without the air going through the injectors. Even with baffles in the tank you will run into instances when air is sucked into the system (Bubbles,sloshing, low tank, hard launch, etc).

A carb can "burp" the air out through the floats. But the only way to "burp" an EFI system is back into the fuel tank.

This means there must be a path the air can travel all the way back to the tank.



What you describe here is 1/2 of a "surge tank" setup. Check out this webpage for a great description of what a surge tank is and does. http://toyotaperformance.com/surge_tank.htm

What I was thinking is a return line to the tank but adding the extra line prior to the tank to take advantage of the extra returning fuel using a low loop to allow air, if any to head to the tank, while the fuel goes to the pump in the on position. The other idea I had was using the filter as a storage or header tank. (dual purpose) They make some larger filters that would hold at least 2 quarts.

 

[ForceFed70]

What I was thinking is a return line to the tank but adding the extra line prior to the tank to take advantage of the extra returning fuel using a low loop to allow air, if any to head to the tank, while the fuel goes to the pump in the on position. The other idea I had was using the filter as a storage or header tank. (dual purpose) They make some larger filters that would hold at least 2 quarts.

The filter for a surge/header tank would work well. I've seen a few pictures of this done and it looks nice and clean.

I think I understand your idea about adding a 2nd line... but I don't think a regular fuel line will be wide enough to allow the air to properly seperate and rise to the "upper" path. The fuel moves through those lines awefully fast. When I put an ear to the filler neck, the fuel returning to the tank almost sounds like a garden hose running in there.

 

[67coupe351w]

So actually after I went off half cocked and wrote the below I see the "surge tank link" is alot like what I decribed:
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I'm considering (and probably will use) a header tank for my Megasquirt install. I learned about it on a SN thread from a few weeks ago, i think it was called "EFI checklist".

But anyway, its a smaller tank (holds enough fuel to run the car for a few minutes) with a submersable pump in it., the header tank is fed by either gravity or a low pressure pump from the main tank to the header tank as well as the retun fuel is emptied into the header tank. Apparently the design was drempt up by Rock crawling efi conversion broncos who's baffless tanks become useless as they travel up the side of a rock.

I'm thinking that if I gravity feed the header tank from the main tank and run the return to the header tank I should be golden.

Suggestions? Comments? Concerns?

 

[ForceFed70]

So actually after I went off half cocked and wrote the below I see the "surge tank link" is alot like what I decribed:
-------
I'm considering (and probably will use) a header tank for my Megasquirt install. I learned about it on a SN thread from a few weeks ago, i think it was called "EFI checklist".

But anyway, its a smaller tank (holds enough fuel to run the car for a few minutes) with a submersable pump in it., the header tank is fed by either gravity or a low pressure pump from the main tank to the header tank as well as the retun fuel is emptied into the header tank. Apparently the design was drempt up by Rock crawling efi conversion broncos who's baffless tanks become useless as they travel up the side of a rock.

I'm thinking that if I gravity feed the header tank from the main tank and run the return to the header tank I should be golden.

Suggestions? Comments? Concerns?

Yup.. same sort of thing, although putting the 2nd pump inside the tank is a new idea to me. I don't see why it wouldn't work.

Gravity feed may be difficult. There's not many places you could install a header tank that would be lower than the bottom of the fuel tank. If you were able to find a spot a little lower than the tank, I don't think the few inches of drop would be enough to get a fast enough flow of fuel.

 

[red65]

Yup.. same sort of thing, although putting the 2nd pump inside the tank is a new idea to me. I don't see why it wouldn't work.

Gravity feed may be difficult. There's not many places you could install a header tank that would be lower than the bottom of the fuel tank. If you were able to find a spot a little lower than the tank, I don't think the few inches of drop would be enough to get a fast enough flow of fuel.

You'll need a low pressure pump to keep the header tank full. I don't think you could gravity feed it fast enough (unless you can rig 3" fuel lines...lol).

 

[jikelly]

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