bobbyc Posted October 2, 2007 Share Posted October 2, 2007 i'm building a surge tank for my z....right now it's sittin at about 17oz...whcih seems sufficient buti wanted to get some opinons. i plan on feeding it initially with the stock FI pump and then a walbro 255 after that ....the shape is just cylindrical...i was thinkin about a conical bottom but i think i flat bottom on both ends is enough (need help there) ...all the cylinder has to do is stay full and i don't think that will be a problem...esp with the return line being fed back into it. i'm welding 6AN bungs at all the connections. one question i have is...will the pressure of the return line increase if it's pumping into a full surge tank...i will have a line from the surge tank going straight into the fuel cell. thanks guys and sorry for beatin a dead horse...i didn't see any post in reference to size. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 2, 2007 Share Posted October 2, 2007 A conical end is more important if you have a surge tank that is wider than it is tall. The smaller diameter and taller you can make it, with the fuel connections for filling and return at the top, the better. If you have a 4" diameter tube, I'd cone the bottom for a 1/2" (-8)pickup if the tank was not at least 8-12" tall (including the cone). A 3" diameter tube, I'd cone if it wasn't at least 6" tall. Usually 2X diameter of the tube will be enough to separate any air bubbles that may get in there and want to get sucked down into the intake for the main pump. As far as flow goes, 3/8" (-6) line will be more than enough for most pumps, and if you can't get a positive pressure number in the surge tank at idle (1-2psi maximum at full bypass, minimum fuel requirement, maximum pump output flow) then you can always insert a small orifice into the return line to boost your surgetank pressure. If you build the return line to the tank from the surgetank oversized, you can always orifice the line. You build it too small, and you're cutting and welding something that has had fuel in it... For a stock setup, on a stock L28ET, I used 8mm return lines, a 10mm feed line from the boost pump, and a 12mm line for the EFI pump pickup. And that was using one of the 6mm emissions vapor barbs on the top of the 240 tank as the return point. Sucking out of a stock 240 tank, even during hard cornering I never had a hiccup with that setup. As I recall, the boost pump I was using had an internal cutoff at 2.5psi for carburettors, and occasionally I could hear it shut off and turn back on at idle, so my maxumim surge tank/return line pressure was probably around 3psi. Tank was 75mm in diameter, and basically was slightly shorter than the length of the upright that goes from the floor to the rear lower control arm behind the differential on an S30. Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted October 21, 2007 Share Posted October 21, 2007 I hardly think that the surge tank would ever not be full once it's been filled. With an open discharge fuel pump feeding it, it should keep up with whatever 'bigger' pump it is feeding unless you use an ancient 80 lph feeder pump to feed the surge tank and a monster Weldon afterwards. Even then, the 'bigger' return fuel is fed back into the surge tank, so all the feeder must do is keep up with actual fuel usage in a near 'open discharge' environment. Quote Link to comment Share on other sites More sharing options...
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