DIY Fuel tank

[ROBBIE]

Few weeks back I struggled to follow Steve up over a hill with quarter of a tank

[Jordi]

Don't ever intend it to be that empty when I'm off roading. May make it quite deep to prevent running it too low. Just loads of ideas being thrown around at the moment.

[Edweird]

We had a similar issue with the Formula Student car's fuel tank, although it was due to cornering forces rather than incline angles. As the fuel system was my responsibility, I countered it by having a swirl pot type thing on the bottom of the tank, rather than having an actual swirl pot and a lift pump in order to save weight.

[Ladaman]

That's a nice idea Edwierd.

If you made the hole from the main tank to the lower swirl pot type tank not too small it would stop the fuel running away on hills.
And if you put the fuel out, maybe 25mm from the base, instead of at the lowest point, then you wouldn't suck crap out of the tank all the time.

[ScottieJ]

All depends how much of an angle you are at and for how long. A V shaped bottom won't really help if you are close to 45* and even with baffles the fuel can still drain to one side of the tank, just takes a bit longer.

What ed posted up is pretty much the best solution I think, it's the sort of thing I was going to do, personally I would rather have a tank with close to stock capacity to save carrying around loads of extra fuel/weight that you might not necessarily need for a day out offroading.

[Edweird]

That's a nice idea Edwierd.

If you made the hole from the main tank to the lower swirl pot type tank not too small it would stop the fuel running away on hills.
And if you put the fuel out, maybe 25mm from the base, instead of at the lowest point, then you wouldn't suck crap out of the tank all the time.

The diagram I made isn't entirely accurate. The take-off point was actually about 10mm up from the bottom and protruded inside the 'swirl pot' about 10mm too. The reason I put the lip there was for precisely that, to help keep fuel from coming back out of the pot. I found that, after some fluid simulations and calculations, this method with the dimensions of the one we built (in theory, though it never let us down) works better than baffles and equally as well as a separate swirl pot, up until the vehicle reaches I think 3G perpendicular to gravity, which would equate to a vehicle tilt angle of about 70 degrees. If you can get your SJ over that far I think fuel delivery is going to be the least of your problems.

The taller and skinnier you make the swirl pot, as well as the smaller the drain aperture, in the bottom of a tank like this the more extreme the angle, or cornering G you can pull without the pump sucking air.

[twiss]

Looks like a good idea! You could probably incorporate a sensor for the fuel light quite easily... as in if there is no fuel above the swirl pot you need to fill it up quick

[Jordi]

Petrol only has an SG of 0.737 so an extra few litres isn't going to exactly weight it down or affect performance.

[Edweird]

Looks like a good idea! You could probably incorporate a sensor for the fuel light quite easily... as in if there is no fuel above the swirl pot you need to fill it up quick

Yeah, you could weld a bolt onto at the bottom of a side on the main tank over a hole and get a sensor that just threads in. I'd put it at a height so you'd have about a gallon left on flat ground.

[dazerede]

On the Sj I'm breaking it had a big metal jerrry can with 3 3mm holes and a bit of metal pipe coming out and then the fuel pipe clamped on good setup for a off-roader I think also had a metal frame to hold it in there only pic I had