ANTI-SURGING OCTANE

DESIGN AND BUILD YOUR OWN SURGE TANK

Welcome to the Weekend Workshop, a place where you can save some cash by getting your hands dirty. These tech guides aim to arm you with the necessary info and knowledge to get out there and give it a go yourself, with no professionals needed, and at a price tag that won’t break the bank.

This month, we delve into building a surge tank with the help of Quest Fabrication. The purpose of a surge tank is to ensure that your engine has a constant supply of fuel. At high G-loads, a regular fuel tank will often experience fuel surging — a condition where the fuel shifts away from the pickup under load. By adding a surge tank, you’re ensuring a constant supply to the engine, even if the tank pickup is experiencing this surging.

While you can purchase plenty of off-the-shelf surge tanks for some pretty good prices, often they are not fit for purpose — either they are too small in capacity, have the wrong fittings, or are the wrong shape for your application. What we’re building is a 10-litre large-capacity surge tank that is capable of feeding E85 through a pair of Bosch 044s at full duty for a decent period of time. As this tank is for a circuit car, we also want to add a little capacity to the overall fuel system to give us a few more laps in reserve.

We then stamp the cap in the press to give it some shape and strength, using a custom-spun buck, similar to a dimple die. If you wanted to give the tank a professional look, alternatively, you could order a set of spun caps from your local metal spinner (very cheap). If you use flat or pressed caps like we do here, you’ll want to ensure that the diameter of the finished product is 1mm under the pipe’s overall diameter, to give a good channel for welding. If the two pieces butt up perfectly, it will be much harder to lay them dimes without overheating the cap edge and blowing a hole.

The base will seat the two Bosch 044s directly onto it using threaded alloy weld-ons — we do it this way to simplify everything and cut down the amount of expensive AN fittings and hose needed. We then use a 50x3mm alloy strap to give us the height. This could be higher or lower depending on what alloy you have on hand. You don’t want to make it too thin, as it will affect flow to the pumps.

The shape of the top of the tank will match the base, which will house the -10 feed, -8 return from the reg, and -8 overflow return to the main tank. These can also feed directly out of the top if you chose, or directly on the side of the tank. It all comes down to personal preference.

We choose this shape to help the tank look more balanced due to our excessive height.

With everything mocked up, we also run the tube through the bead roller to give it some shape, purely for aesthetics. The thick sidewall really works the roller, but we get it done in the end. Before final welding of the tank, the AN weld-ons are all welded from the back side, so that the finished product will have a cleaner and more professional look.

Alloy welding is not really our strong point, so, at this stage, we kind of cheat and have Kyrie from Quest Fabrication man the TIG torch. With any alloy welding, cleanliness is the key to achieving a good bead. This can begin from as early as cutting the alloy-specific cutting disk, and using a new sanding disc to avoid contaminating the alloy. Just prior to welding, we give the edges a good run over with a Scotch-Brite scourer and clean with acetone.