fuel tanks

[slangley]

There are three fittings on each tank. One obviously for the fuel pump. I have noticed that a number of builders have connected the upper fitting as a return between the tanks.

My question is, wouldn't the bottom fitting be used to connect the two tanks together and the upper fitting used as the return line from a pressure regulator?

-sml-

[davefiddes]

The upper fittings are used to link the tanks together so it is harder to overfill one tank.

One of the bottom fittings has an internal pipe that goes to the bottom of the tank and is for fuel pickup. The other is for pressure regulator return (carb or EFI). You don't want the return going into the tank at a high level because it'll froth it up unnecessarily and cause the fuel to go stale (as well as generate lots more vapour). Some people have change the fuel tank fitting as the bottom to be -10 rather than -6 to allow a bigger link pipe to be used. This means that their fuel tank behaves as a single tank. If you don't put a big pipe between them then this won't work.

[steve_D]

My tanks are linked top and bottom in -6. This should make filling from one tank possible but perhaps a little slow. My pumps deliver -6 to a 'Y' piece and comes out -8 to go to the carb. If I get to a point where one pump at -6 is not enough then I will rewire them to run together when required.
Steve

[mkoch1]

If you use the upper fitting to connect the tanks it will only balance out the fuel until the fuel level goes below the fitting. If you are running 2 pumps this may work as long as the balance line can keep up with the fuel returning to the tank.

I am using the top fitting for the return from the surge tank. I had the lower fitting replaced with -10 fittings. I am only running one pump, pulling + returning to the same tank so I needed to make the second tank an extension of the first.

mark

[bigmack]

Hi Mark,
According to my owner's manual, Ultima mentions linking the top fittings together for overflow when running two pumps. Otherwise, if you run 1 pump, then you are right, once the level gets below "Full" the tanks won't balance out. It shouldn't really be called a balance link pipe, but an overflow link pipe.

I've set mine up so that the tanks are linked at the low fitting, and use one of the top fittings for a return line. These tanks are filled with foam to keep the frothing down. I've plumbed mine according to some documentation I got from Kinsler one time. From my experience, the balancing out of the two tanks with -6AN line is a little slow. One person I know, had a pump for transfering fuel over from one tank to the other to speed this up. Then he ran another pump to his surge tank and another pump from the surge tank to the engine. That's a lot of pumps. What I've been toying around with is the idea of pulling from both tanks at the same time with one pump, which would feed a surge tank, and then using another pump from the surge tank to the engine. The return from the carb/injection should go back into the surge tank and an overflow from the surge tank back into one of the fuel tanks. Then keep the low connected balance pipe. How does this sound?
Cheers!
-Mack

[steve_D]

bigmack said:

........ What I've been toying around with is the idea of pulling from both tanks at the same time with one pump, which would feed a surge tank, and then using another pump from the surge tank to the engine. The return from the carb/injection should go back into the surge tank and an overflow from the surge tank back into one of the fuel tanks. Then keep the low connected balance pipe. How does this sound? Cheers! -Mack

The only problem I see there is that if one tank line pulls air due to surge then that is all you will get as it is the line of least resistance.
Steve

[gdr]

Upper link as Mack says is an overflow incase NRV fails in dual pump set up and active pump starts putting fuel through inactive pump into other tank. Would this actually stop overflow of inactive tank, as these pumps put out a fair old flowrate? Might pressure up inactive tank a bit as the -6 overflow will be a bit of a restriction.
I'm working on a switch to EFI, whats the best way to plumb 2 tanks for this with return line?

[davefiddes]

gdr said:

I'm working on a switch to EFI, whats the best way to plumb 2 tanks for this with return line?

I'm stuck on that one too. The feed seemed easy enough: replace the pipe to the carb on my std dual pump setup so it goes into a surge tank. A -8 out from there to the high pressure fuel pump. Return from the regulator feeds into the surge tank.

The overflow from the surge tank is tough. People I've heard of with dual tanks that have just put a Y splitter to return to both tanks get erratic filling of both tanks (depending on cornering, tank height, etc).

I wondered about a 3-way solenoid valve that could be held open by one of the low pressure pump circuits. I've not managed to find anything suitable yet. I did come across a nice valve that Hilborn make but it was just the valve and would need some sort of actuator. Looked expensive too.

[bigmack]

Didn't think about the fuel surge issue. Hmh...so maybe its back to 3 pumps.

Steve, how's the car coming along?

Cheers!
-Mack
p.s.I take mine down for inspection on Monday. Something I should have done 3 years ago when I finished the car the first time! I'm still considering a whole host of other mods, but my wife told me she's finally fed up with my chasing these crazy dreams. "Dress it up as nice as these other Ultimas in the magazines and get it on the road, or sell it and be done with it!" Well she may have said it with a few more choice colourful 4-letter words.

[steve_D]

bigmack said:

Didn't think about the fuel surge issue. Hmh...so maybe its back to 3 pumps. Steve, how's the car coming along?

It goes to the factory Saturday.
They will do their bit then it's booked for SVA Monday 10th.
Steve

[UltimaLVR]

Check this thread on another board talking about GT40 fuel systems...

[URL]GT40 Fuel System |www.ffcobra.com/ubb/ultimatebb.php?ubb=get_topic;f=36;t=000549#000000][/URL]

[Stig]

Chaps, this subject comes up fairly frequently and has been covered in depth in the past, however, I can tell you this:

1) There is no need to replace the -6 fittings unless you want to be able to fill from one tank only (let's face it, it's no hardship to fill both sides of the car and it gives you more posing time at the pump )

2) The carter fuel pumps provide WAY more supply than you can use. I've had my car full chat round a circuit and the fuel pressure was constant.

3) Like 2, if you're getting enough fuel surge to cause starvation, then you'll be more concerned with peeling your face off the side window under g-force Providing there's a reasonable amount of fuel in the 'outer' tank and the corner isn't a mile long you'll be fine. Fit a swirl pot if it makes you feel safer but IMHO it's not needed.

[davefiddes]

Stig said:

Fit a swirl pot if it makes you feel safer but IMHO it's not needed.

This is true if you are running carbs (which have built in mini surge tanks called float bowls). All EFI installations have to have a surge tank to stand any chance of guaranteeing a constant fuel supply. Even Nissan Micras and Ford Fiestas have a special sump built into either the fuel pump or fuel tank. If they didn't, even in normal road driving, the engine would be toast when the tank got below about 1/3 full.

[Stig]

davefiddes said:

Stig said: Fit a swirl pot if it makes you feel safer but IMHO it's not needed. This is true if you are running carbs (which have built in mini surge tanks called float bowls). All EFI installations have to have a surge tank to stand any chance of guaranteeing a constant fuel supply. Even Nissan Micras and Ford Fiestas have a special sump built into either the fuel pump or fuel tank. If they didn't, even in normal road driving, the engine would be toast when the tank got below about 1/3 full.

Fair comment Dave, but 99.5% of Ultima's run with carbs.

Still, it's the exception that proves the rule 'innit

[454]

There was a thread a while ago regarding this topic, here's a quote from Jeff on his setup :

"I'm running a single Holley 12-920 (225 LPH)inline EFI pump, basically I have a Y off both tanks, through a single filter, feeding the pump. The return goes to the Aeromotive 13109 regulator first, then to a Y back to both tanks. EFI pressure is supposed to be regulated after passing through (or on the way out of) the rail.
11,000 street, miles 2 road course days, 50 drag strip passes, 2 time trials, no problems.
jeff"

My setup will be very similar as this has obviously been reliable and is very nice simple way of doing it.

Jez


>> Edited by 454 on Friday 30th April 10:34

[davefiddes]

Stig said:

Fair comment Dave, but 99.5% of Ultima's run with carbs.

Sadly.

[gdr]

I'm running a single pump on carb right now, no problem with -6 fittings, agree with Stigs sentiments on filling station convenience (just be sure to stop close enough for nozzle to reach outside filler to avoid ruining the pose). My thinking for EFI is to base system on a single tank, draw and return to this tank and run a low link pipe (-6) to allow other tank to top up active tank just by gravity. Not convinced of need for surge tank on EFI, pick up design and foam should help avoid fuel starvation, but safest route I suppose - there goes another £100 into my low cost EFI project!

[andycanam]

even when linked there is at least 5litres in each tank that cant surge from one side to the other due to the outlets being 2.5inches from the bottom of the tank.
They are also foam filled.

[jschwartz]

yep, just like it says above. Except I've now got 12,000 miles and another track day with no fuel system problems. I also added a 100 hp NOS shot, still with the single Holley EFI fuel pump.
jeff