NZ Performance Car - - Con­tents -

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.

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