EFI Mods to 73 Fuel Tank

[markandson]

True, but what I meant was if you filled the tank all the way to the top and covered both holes. As you are filling the tank there is no way that the bowl would fill up as fast as the pump is filling the tank, so you could trap air inside the bowl once the top hole is covered. It appears that the hole is so close to the top that the gas would have to go up into the filler neck in order for this to happen.

[namba209 (R.I.P.)]

Yep, that's true Jeff. The gas nozzle would shut off automatically before that chamber would fill up. The reason for the chamber, so I was told, is beause the gas in the underground tanks is much cooler, when it comes out of the nozzle, than the ambient temperature, at least other then winter time, that when it does go into thermal expansion, the gas has a place to go, other than dump on the ground via the filler neck. Maybe. Anyway it sounded good when it was explained to me.

[neuropel]

Hmmm...does my Manta fuel tank have the same soup bowl?
I have a couple more questions regarding fuel tank mods:

1). Is there any reason to change out the size of the fittings on a '75 tank from an EFI car? I'll be running twin weber throttle bodies on the 2.5 with the big valve 2.4 head. I don't want fuel starvation issues.

2). If you're modifying a pre-'75 Manta tank (we're talking another car here now), where do you prefer putting the fittings? I notice the sender is in a different location on the '75 factory EFI tanks.

Thanks,
Todd

[namba209 (R.I.P.)]

Todd, mechanical fuel pumps and almost all electric low pressure fuel pumps are of the flow bypass type. That is they will only flow fuel if there is a place for it to go, i,e. the float needle is off the seat in the carb float bowl. Because the EFI system flows at a higher pressure and dumps excessive pressure back to the fuel tank, the fuel line from the tank should be more than sufficient to handle a pair of carbs at lower pressure. HTH.

[markandson]

An EFI pump is a positive displacement pump, it can have an internal relief valve that causes the gas to recirc. inside the pump if the outlet pressure reaches the relief valve setting. The other choice is to not recirculate within the pump but to send the excess flow back to the tank once the relief setting is achieved. The return line size is dependant on the flow capability of the pump, and the amount of fuel that the engine uses, not the pressure. If the return line is too small it will cause the system pressure to become higher and also unstable which will cause flow variations at the injectors.

[neuropel]

Thanks for the info guys. Following RallyBob's advice, I've been planning and working toward the buildup of my 2.4. With pistons I got from Bob it's actually going to be a 2.5. After installing the bigger valves in the 2.4 head, I had Bob port the head and twin intakes, but rather than running carbs I plan to run something like the throttle bodies from TWM Induction. As such, the engine will likely suck fuel pretty good and my concern has been that the fuel line sizes in/out of the tank may need to be increased...perhaps that's not the case? I'm unsure as to which fuel pump I'll be using, and I haven't searched here yet to figure that out (and it's quite a ways out anyway!). I'd like to use something QUIET, reliable, and up to the task.

Good info in this thread!
Todd

[namba209 (R.I.P.)]

Oops. my bad. When I read Todd's post and saw Weber, I automatically thought carbs, and didn't read throttle body. On Willit? I used two pumps, two filters and two tanks, after reading and discussing this in the chat room. The reasoning is that the shape of the GT tank will cause the fuel to slosh away from the main tank outlet under spirited driving with about 1/4 or less fuel in the tank. As I said in post #9 of this thread, with the engine at idle and both pumps running, the 1/4" return line to the tank appears to be sufficient to handle the total return flow from the surge tank, high pressure pump return/internal bleed, and fuel rail return flow. Quiet pumps are a must! I had two solenoid type pumps back by the tank and they drove me crazy. I've now got a rotary vane type going in today and it is a lot quieter by a bunch. The high pressure pump feeding the fuel rail is a gearotor type and is also very quiet. You'll need to talk to the TWM folks and find out what pressure and flow their throttle body setups need. Then go to your local auto parts store and check out their fuel pump books. I spent about an hour going through them to find the pumps I wanted for Willit? and then built the system around the pumps. Both the pumps I'm using are expensive, over $100 each but they are quiet.

[markandson]

Here are the pics of the finished hole, with the frame (with tack welded nuts on the bottom) plug welded to the inside of the tank, and then ground off smooth. The cover is 1/8" steel with a ultra seal gasket fitted and stainless hardware. The only thing left to do on this part is sand blast the cover and paint. Next I have to install the pick-ups, and the return line, which is why I cut the hole in the tank in the first place.

[jordan]

Jeff, it doesn't look like you used any type of doubler inside the tank to reinforce the captured nuts. It looks like it was done well but I would still fear that it would leak from distortion of the top of the tank when the bolts are tightened.

[markandson]

Jordan, Go back and look at post 15, the square frame, made from 1 x 1/8" is what the nuts are welded to and what is inside the tank.

[markandson]

Added the pickups today, still need hose clamps, and outlet plate needs to be welded to bottom of tank.

[RallyBob]

Looking good Jeff. Tell me, are you using the proper 'submersible' hose for the pickups? I ask because using normal fuel line will eventually result in the lines softening, with the end result being the lines will collapse under vacuum. I learned the hard way many years ago...

[baz]

the first photo looks bad when the pipe has "not for fuel" printed on it

is this the right kind of hose ??? i guessing it says not for fuel injection when read in full

[markandson]

Baz, I took the darn pictures and didn't notice that . Yes it is not for EFI. But RallyBob has caught me. No I did not use submersible fuel hose, didn't know it existed. So where do I get this stuff, I need about 18" of 3/8 ID. Good thing I am still in the middle of this mod, and posting my progress.

[RallyBob]

No I did not use submersible fuel hose, didn't know it existed. So where do I get this stuff, I need about 18" of 3/8 ID.

I got mine from Auto Performance Engineering. It needs to be SAE J30R10 rated, rather than J30R9 rated.

I suspect you can use the same stuff that fuel cell manufacturers use as well (ATL or Fuel Safe) for their in-cell applications. Keep in mind that prior to the pump the hose does not need to be EFI pressure rated, since the hose is not under pressure, but rather a slight vacuum.

Bob

[markandson]

Interesting, before you posted I went to McMaster to look. The SAE hose that they list for gas use is all Buna-N material for the ID. The hose that they list as having a Buna-N OD is SAE 30R3 which was what I thought I might have to use. Seems to me if Buna-N is good for the ID it should be good for the OD. Maybe I can find the specs on the two to find out the difference.

[markandson]

The plot thickens......Auto Performance only has 5/16" ID available. Bob, did you use 5/16 when you did your tank, or 3/8? The guy at Auto Perf. says 3/8 ID hose is harder to find than Hens Teeth.

[namba209 (R.I.P.)]

Jeff, with a little "Vaseline" 5/16" hose should slide over 3/8" tubing. Or another possibility, depending on the spigots of the remote pickups, use tubing all the way with gas line compression fittings from your local "Home Depot". Just a couple of thoughts. On Willit? I spent a ton of bucks using AN fittings, but of course all my stuff is exterior so I'm not as limited in the grade of hose to use.

[RallyBob]

Jeff, I ended up using 5/16" line. Since I used multiple inlets (3), there shouldn't be a restriction issue.

Bob

[markandson]

OK, since I have 2 inlets I doubt I will have a problem either. The biggest concern I had was the thin wall of the plastic pickup outlet barb. I was afraid too much pressure would crush/damage them over time. I found a guy who says he could get the 3/8 id from gates, but it would cost $300/ft......no that is NOT a typo . I will go for the 5/16"