StolenFox

Trying to decide on a fuel pump and need the advice of this group. My 6.0L will make an estimated 450HP flywheel and is naturally aspirated so a 255LPH is all I need but at some point I may go forced induction and need a bigger pump. The brand I am looking at offers both the 255 and the 340 with basically the same amperage draw and only a $5.00 price difference. Any downside to just getting the bigger pump from the get-go? The install is complicated (BMW E39 fuel module with an extra fuel level sender attached) so I'd like to engineer the setup once and be done if there is not downside to extra flow capacity. I am running the C5 filter / regulator if that helps any.

Thanks for any info / opinions provided!

S.F.

gametech

iTrader: (1)

The downside to a bigger pump tends to be recirculating the fuel to the point of heating it excessively. This tends to generally only be problematic with very large pumps and low amounts of fuel in the tank. I don't see the 340 causing any problems.

ScottyBG

On the GM F-body in tank regulator the 320/340 pumps get a little pressure creep at idle because they flow a little more than the regulator is rated for. I'm not 100% sure if this is true of the C5 regulator, but I suspect they respond the same. Instead of the 58 psi you should have you get something like 65 psi at idle. Once the throttle is opened and a little fuel is consumed via the injectors, so not so much volume is flowing back through the regulator, then the regulator resumes its set pressure of 58 psi. This slight increase is fueling is normally taken care of in the tune, by adjusting idle fueling. The extra pressure would make it a little rich at idle, but it small enough it is easily compensated for via the ECM. Some people with bigger pumps don't really even know this, they put the pump in, tune the car and all is good. The only time you might notice it is if you had the car tuned on a 255, then swapped to a 340. This is not really a problem, just something you need to consider. This I believe is one of the reasons you still see 255's used in dual setups. When running only 1 pump at idle you don't have the pressure creep.

Honestly if your thinking boost, I'd recommend looking at a walbro 450 as a minimum, and strongly consider a dual pump setup. Both of these options carry some more baggage, like fitment, more complex wiring for the duals, and the single 450 really should have a different regulator. Then you probably start considering a return line from the rails. Also the higher BSFC of a turbo or supercharged engine , and they way they like E85, you may want to have that option open. Pushing against a pressurized intake manifold also reduces the pumps flow rate. Your 340 flows about 260 at 75 psi, depending on the pump design, and voltage, maybe a little more or less. My point here is you can run out of pump fast, in a boosted setup with all these factors working against you. On a boosted 6.0 either a 255 or a 320/340, is "fishing with really thin line".

Might be best just to meet your current needs, then worry about a fuel system to support forced induction later? It does bring considerable cost and complexity, that may never be needed if you decide not to go forced induction.