S2 with two fuel tanks

[exarkun1178]

Just ordered two fuel tanks for my S2.  I intend on using the car to commute to and from work, 155 miles round trip 5 days a week.  2 tanks with 8 gallons each X40 mpg highway = ~640 miles per fill.  Not happy about the added weight, but it is more then made up for with 1 fuel stop a week.

Has anyone else done this?  Tips tricks suggestion?

Thanks

[Mecky]

Hi,

we have two fuel tanks in our S2 race car. The problem is that you are not able to connect them with a large tube to make the levels stay equal. Because of that you have to use at least two fuel pumps. Also two fuel gauges or at least a switched gauge to be able to check both fuel levels.

If one pump is stronger, one tank is going to be empty earlier. That was our problem until the worse pump died. Now we use one pump from each tank to a one litre catchtank and a third pump from the catchtank through a fuel pressure regulater to the carburettors. I hope that is the final solution for that problem.

Best regards

Stefan

[exarkun1178]

That sounds complicated.

My initial though it to have a a 1/2" ID fuel hose connecting the two tanks. and use the drivers to deliver fuel to engine. 

Where did you put the 1 liter catch can? 

[jbcollier]

A well set-up racing vehicle is entirely different from a well set-up street vehicle.  Your idea of using a 1/2" connecting hose between the two tanks will work just fine.  I plan on doing the same with my S1. 

If you plan on driving at racing speeds on the road then you will indeed have an issue.  My advice?  Don't reach for the soap in the prison showers...

[exarkun1178]

My commute on the NJ turnpike and parkway will see regular speeds of +80 mph  i expect to run at 4500 rpm at 80.  There will be few if any hard cornering. 

The thought of filling the 8 gallon tank every day or two sounds annoying. 

My one concern is the gas in the bottom of  tank 2 that is not high enough to gravity feed over to tank 1.  i suppose this may be a problem.  a fuel pump would resolve this, but adds complexity.  I want to avoid complexity. 

How does the twincam do it? manage the two tanks?

[jbcollier]

Yes the slave tank will have remaining fuel but the gauge on the main tank will (hopefully) be accurate and, when it says empty, you'll be out of accessible fuel.

You could also have a change-over valve before the pump and run the tank without the gauge dry first.  Or use a change-over valve and switch, similar to a Jag with twin tanks, and run senders in both tanks and the gauge reads whatever tank you are running from.

[EuropaTC]

How does the twincam do it? manage the two tanks?

Pretty much exactly as you plan to.

My twin tanks are linked with conventional, 1/4" internal bore pipe which goes through rubber grommet holes in the chassis, it's the same fuel line that's used for the rest of the system.  The lines connect into a T piece at the RH tank, and the other leg of the T feeds the pump.  The petrol tank sender is fitted to the LH tank and of course both tanks have their own filler neck.

There are no problems in level equalisation in use, but if you want both tanks full to capacity then you will have to fill them separately. You're adding fuel through a 1" (?) pipe and obviously a small bore pipe isn't going to adjust levels at the same rate because the static head isn't going to generate enough flow. I usually fill up one tank to the brim, then move over to the other to top it off.  No great hassle.

Brian

[exarkun1178]

Thanks for the feedback.  Suppose i have another 4 weeks to work out the solution.

[HealeyBN7]

How does the twincam do it? manage the two tanks?

I usually fill up one tank to the brim, then move over to the other to top it off.  No great hassle.

Brian

It used to be that the gas pump hoses were long enough to reach to both tanks.  Now I find myself moving to another pump, or turning around to top off.  If the gas station is not crowded - no big deal.  If it is, then I have two credit card transactions, within a couple minutes which results in a call from Fraud Alert. I do which I would have installed a larger then 1/4" balance pipe. 

Dean

[3929R]

How does the twincam do it? manage the two tanks?

I usually fill up one tank to the brim, then move over to the other to top it off.  No great hassle.

Brian

It used to be that the gas pump hoses were long enough to reach to both tanks.  Now I find myself moving to another pump, or turning around to top off.  If the gas station is not crowded - no big deal.  If it is, then I have two credit card transactions, within a couple minutes which results in a call from Fraud Alert. I do which I would have installed a larger then 1/4" balance pipe. 

Dean

I just filled up this weekend and the hose reached across with length to spare.  I wonder if California pump hoses with their vapor capture/return lines are across the board shorter?

[Grumblebuns]

At my local Shell station here in So Cal, the hose will reach over to either side with no problems. I do have to use a plastic funnel to do the fill up to keep from splashing fuel out from the filler opening.

Joji Tokumoto
FAllbrook, Ca

[Serge]

How does the twincam do it? manage the two tanks?

Pretty much exactly as you plan to.

My twin tanks are linked with conventional, 1/4" internal bore pipe which goes through rubber grommet holes in the chassis, it's the same fuel line that's used for the rest of the system.  The lines connect into a T piece at the RH tank, and the other leg of the T feeds the pump.  The petrol tank sender is fitted to the LH tank and of course both tanks have their own filler neck.

There are no problems in level equalisation in use, but if you want both tanks full to capacity then you will have to fill them separately. You're adding fuel through a 1" (?) pipe and obviously a small bore pipe isn't going to adjust levels at the same rate because the static head isn't going to generate enough flow. I usually fill up one tank to the brim, then move over to the other to top it off.  No great hassle.

Brian

This is also the way I will do it. Two tanks, two fillers, bigger connecting hose with a Y-piece in the center going to a single electric fuel pump. To make sure that you don't pump fuel from one tank into the other, you can add non-return valves in the connecting-hose. Hopefully they will get empty at the same rate, in this way also making sure that one fuel sender will suffice.


Serge

[EuropaTC]

I took a shot of the arrangement on my TC this morning as pictures are much better than words.  I kept the original design but have changed the rubber fuel lines and the original plastic T piece which I also changed to metal after reading that the plastic had a tendency to crack with old age.

Both tanks have 1/4" outlets and normal rubber fuel pipe. The metal T piece connects both tanks and feeds the fuel pump line, so in practice both tanks should empty at the same rate. There are no non-return valves as the pump can't put back-pressure on the system. It uses a single fuel gauge sender which is in the LH tank, again OEM stuff.

I'm not convinced a larger connecting pipe would make any difference unless you also modify the tanks themselves to have 1/2" outlets, surely the 1/4" outlets will just act as a pair of opposing orifice plates and slow everything down ?

Brian

[Serge]

I agree Brian, a larger connecting pipe will only work if the fuel tanks have bigger outlets as well.

Serge

[exarkun1178]

Do you all think the 1/4" is too small of a connecting hose?  should i request 1/2"?  I imagine if the single tank with 1/4" works then there should be no issue with the same hose feeding from 2 tanks.