I seem to remember they have three lines, two are fuel line size and the other smaller which may be a vent all of them go into the top of the tank.

I'm fairly positive there are three tubes. 8mm supply, 8mm return line, and a smaller (5mm?) breather line. The feed and return are on the metal flange that sets into the tank. The breather is welded into the tank. This is what I've gathered from research. Someone who actually owns one may know differently.

If you're gettingpressure release from the tank, I would venture to say you have a blocked breather. Whether it's capped by a P.O. or just a bad vent tube.

Someone else's response in this thread indicated they thought the SPI/MPI tank was not vented as they would get the pressure hiss when they removed their fuel cap.

That is why I was asking in order to be sure as well.

Thanks for the suggestions, guys. 

Nick, if you have pictures I would love to see them

MPlayle, I believe the factory MPI and SPI tanks are still vented. I was actually told specifically that they are. If this isn't true, someone please feel free to correct me. I don't have first hand knowledge, just what others have specifically told me in emails. 

Picture Nick?

I just added a return to a LWB tank and will be using a surge tank/swirl pot to provide the fuel to EFI.

LWB cars are more problematic. On //www.turbominis.co.uk/ you can find a number of saloon solutions.

Terry

What do you do with the vent pipe on the standard tanks you modify? Do you leave the tank vented?

From others' responses, the SPI/MPI tanks seem to be unvented while the standard tanks are vented.

On the EFI cars I have built I use a Earls AN weld fitting tig welded to the top of the tank, then use a 90 degree fitting on the hose and it makes for a clean instaliation in the trunk. 

Maybe email the folks at Minitec to see how they handle this for their Honda swaps.

Well I considered buying an MPI tank with pump, but everyone either wants a small fortune for them, or they are rusted to hell. My tank is a large tank and nearly perfect as it is, so I see no point "upgrading". I'll probably pay a local welder to weld on the AN fitting and still keep my vent tube on top. I was planning on doing an electric fuel pump anyway, so no harm there. And the money I'll save from not buying the MPI tank will more than cover that. 

So has anyone modified a tank for a return line? I've only seen a couple on TheMiniForum. And the search feature on here is a bit less than reliable so I couldn't really dig anything up.

You've probably already thought of this but will the fuel pump you intend to use have enough pressure for the fuel rail? An MPI/SPI fuel tank and pump were recommended for my setup. Not inexpensive but I think if you price out everything both ways you'll see that it is the easiest and cleanest solution and maybe closer in price than the alternatives.

My thought to offer to consider -  Going with an MPI / SPI tank will have compllete pump in the tank with the return line ready. This has the pump and return all present for a very clean install.

Converting a regular tank - to a closed return system requires you to still have your electric pump and wires hanging all about and somewhere. Will be more noisy and  Simply have more joints and fittings.

Does an EFI Tank need to be ventless? On my SPI- i open the gas cap when  re-fueling and it  gushes our air pressure as if the tank assembly is a closed pressure sysem.  Mk 1- simple vented tank - never vents pressure from the cap and mostly vents fuel from the cap!

I don't think it is the right size Micheal but i guess it could be downsized and used in a push. I modified a tank once when installing twin tanks in an SPI and just used a 2 inch piece of old fuel line with the crimped end flushed out the tank well and left it to dry out for a couple of days drilled the hole and had it welded in with no issues.

What are the differences between an SPI/MPI tank and a regular tank (other than the fuel pump inside the tank)?

I'm leaning towards a pretty trick EFI setup, and if I go this route, I'll need to get a fuel return line plumbed. So I've been looking at two options. 1, just having a shop weld in a return tube or having them weld in some kind of AN fitting that I can use.

Wondering if anyone on here has done this, and how you did it. I know that I could just pick up an SPI/MPI tank, but they are a bit more expensive than I want to go with if I don't have to. Plus, I have a nice 9 gal. tank now that has no rust and I don't see the reason to get rid of it.. unless someone has an MPI tank they want to trade me.