seattlejester Posted March 20, 2014 Share Posted March 20, 2014 Now there is merit to running a bigger return, but only if you are using really really thin lines with more than factory rated pressures. Once you pass the minimum restriction sizing for the pump, return hose line size doesn't really matter. On quite a few high hp turbo cars with aftermarket regulators you actually have a boost reference to the fuel pressure regulator, so the regulator only builds up excess pressure when you are in boost and using more fuel (the increased pressure helps compensate for the extra fuel), so running a larger return then the feed would not serve the purpose of preventing back pressure in the return line. When you have over stock levels of required fuel pressure you are using more than stock levels of fuel so it is a zero sum kind of situation. The pressure in the intake manifold is pushing back on the fuel in the fuel injectors so you need the additional pressure to pump the fluid into the intake, the pressure behind the fuel is overall the same. Most mid range regulators are AN6 size. Running a bigger hose is not going to do much good when the exit port is still restricted to a 6AN fitting. It's like hydraulics, doesn't matter where the restriction is released, once the line is filled with incompressible fluid the pressure is the same. Whether the pressure is released right after the regulator or at the fuel cell it shouldn't really matter. If longevity of the fuel pump is your game, it would be better spent trying to design your fuel system so the fuel doesn't take any slopes to the fuel rail and that your fuel pump is supplied with a steady column of fuel (mounted below the fuel line in the tank or as close to the level if not lower than the sump). I mean this is all from thought, in practice magical things may happen, but theory and practice says otherwise. Quote Link to comment Share on other sites More sharing options...
Ryan Merrill Posted March 20, 2014 Author Share Posted March 20, 2014 My goal is 600 whp. Do you think the 8an feed will be enough. Not sure how much fuel the car will use under full throttle. I was discussing the large return fuel line with a friend today. His personal car is a 1000 HP gt500. He said for very high HP street driven car the return line should be at least the same size. If your cruising down the street 90% of the fuel is returned to the tank. The line has to be big enough to support that amount return fuel. If you almost maxing the feed line and the return line is too small you could have some issues. He said over sizing the return was never required. Quote Link to comment Share on other sites More sharing options...
Avernier Posted March 20, 2014 Share Posted March 20, 2014 Stock jzx100's (vvti1jz) make 600whp, on e85 on stock fuel lines. -6 will definately flow enough for 600whp on pump, and e85 too. Quote Link to comment Share on other sites More sharing options...
Avernier Posted March 20, 2014 Share Posted March 20, 2014 Correct on return line sizing. Think about it, x amount of fuel goes down a line y dismeter, under pressure, and some fuel is consumed by the engine, that means less than x amount of fuel remains to be returned to the tank. No way in hell you EVER need a larger return than feed. Quote Link to comment Share on other sites More sharing options...
seattlejester Posted March 20, 2014 Share Posted March 20, 2014 You can push a small fuel line quite a bit by ramping up the pressure, but that will put quite a bit of strain on the pump. I think a good rule to follow is the funnel rule. Give as much access to fuel as is reasonable. If you have an in tank pump, make sure that it won't starve. If you have an external pump, feed it with the same size fitting on the fuel cell. I think most fuel cells come with a -8, so going any bigger would be a bit silly. If the line is bigger, yes you would technically have more fuel to use before the line is empty, but it would have to draw the extra volume from the smallest restriction to fill up the line. With that said if you are thinking AN6 and have AN8 fittings on your fuel cell I would say to size your lines bigger than you may need (if you have any considerations of maxing out the flow characteristics of AN6). Replacing a fuel pump or a regulator can be easy, but depending on how you route your lines replacing the lines may be quite tedious or difficult. So size one step bigger then you think you will max out at within reason. If you have aspirations for 1000 hp, but realistically only 400 for the next couple years, don't get AN10 or 12, by the time you will need bigger fuel lines you are going to have to address a lot of things with the drive line so it will have to be removed anyway. The consensus was AN6 was good for 500hp on pump gas with reasonable fuel pressure levels from casual browsing. I'm shooting for 300hp, but my fuel pump had AN6 input and output as did my regulator, so I just used AN6. If I ever get close to 500hp, I will probably change my feed line to AN8 to the fuel pump since my cell has -8 outputs, but the AN6 lines should be up for the task of my high end goal (this is also the limit of my cooling, intercooler, and stock internals). Quote Link to comment Share on other sites More sharing options...
grayson260z Posted March 24, 2014 Share Posted March 24, 2014 Sorry to post something that isnt necassarily related but I didn't want to make a whole new thread for it. Do any of you guys have pictures of your fuel cells in the spare compartment with the fuel lines already ran? And also I'd be interested to see how you sectioned the fuel cell from the main part of the cab. Thanks! Quote Link to comment Share on other sites More sharing options...
Ryan Merrill Posted March 25, 2014 Author Share Posted March 25, 2014 Sorry to post something that isnt necassarily related but I didn't want to make a whole new thread for it. Do any of you guys have pictures of your fuel cells in the spare compartment with the fuel lines already ran? And also I'd be interested to see how you sectioned the fuel cell from the main part of the cab. Thanks! go on Hybridz.org, there's a pile of pictures on there. Quote Link to comment Share on other sites More sharing options...
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