Rebuild advice

Discussion in 'Mustang Chit Chat' started by hockeygod, May 12, 2018.

  1. JeremyH

    JeremyH 3V Fuel Guru

    Likes Received:
    Jan 10, 2009
    Virginia Beach
    Her is my 2 cents for fuel based on your entire build of the motor setup, power adder and power/boost goals.

    First off I am a huge fan of hot rodding the returnless system for more power, but you will be on the "ragged" edge if you are serious about 800rwhp with a returnless setup. While it "can" be done with more mods its safer and more reliable to go to return at that level. My general reccomendation is north of 700rwhp its time to seriously think about going return and my hard limit based on physics of the system is around 750rwhp.

    Whats going on is returnless pressure stability starts getting squirelly at high load/boost/rpm above around 750rwhp/20psi or so due to the physical time it takes fuel volume to come from the the tank to the rails so the injectors can supply enough fuel for the air and achieve/maintain the rising delta pressure (base pressure plus boost level onramp). You start seeing latency/delay which causes pressure instability essentially, fluctuating pressure means the injectors aren't consistently delivering the commanded amount fuel every pulse. You can really see whats going on in datalogs at these higher levels, you see lots of pressure spikes and drops in a short period as the boost ramps in and the sytem is trying to adjust and get fuel where its needed. This plays into the tune thing guys talk about it becomes more of a challenge with these physics.

    Thats the fundmanetal difference in return vice returnless. Returnless you are relying on that rail sensor to tell the pcm and then pcm to control the driver modules and then the pumps speed up, then the fuel volume has to physically move from the tank to the rails to supply the injectors and keep pressure. This system works great at moderate boost levels and flow levels. If you think about it, dual higher flowing pumps being fed increased voltage by baps at full tilt are supplying 3-4 times the amount of fuel over the stock system at these 700-800rwhp power levels. So if you look at how quick a wot blast hit from 2k to 7k rpm and from vac to 20+ lbs of boost is. Thats how quick all this has to happen to get more and more pump speed and fuel up to the rails.

    Return functions in the oppostie manner essentially, the pumps aren't repsonding to pressure changes to change volume output, instead the pumps are run full on/full ouput so fuel volume to support the power is always at the rails for the injectors to use. And then a mechnaical vac/boost referenced regulator seemlessy maintains delta pressure as you transitions from idling to full boost. The volume to support the power is physically always there the regulator just returns more or less fuel back to the tank based on load/demand. This mechanical regulator mounted right by the rails responds instantly so there is no time latency. This is why a return system has stabil pressure and can safely support more power. There is no sensor to signal to driver to pump to sensor to signal feedback loops going on. lol

    To try and stay returnless at the 800rwhp level here are mods you will need, you will want a 6-8awg power wire upgrade to the relay and same size from relay into the dual bap and then 8-10awg wire upgrade from the bap outputs into each fpdm. This is crictical so the pumps dont suffer hot flow loss from increasd current draw at the higher voltage levels. Next you have to reduce restriction in the flow path of that fuel from the tank to the injector, so aftermarket rails and a 8an line and high flow filter upgrade from hat to rails will be needed. The stock line rail connector has a 4mm diameter hole that all the fuel is trying to get through to get to the rails. The pprv on the fuel hat has a 6mm inner diameter hole, so that another restrcition to address and you will want to remove that valve from the hat. After that your looking at some dw300m 340lph pumps to swap into the gt500 hat which are the largest pumps the drivers can handle before thermal shutdown from excess current.

    People are often intimidated or swayyed by the higher intial cost of a return setup. But if you look at all the costs here and there of that fully ugraded returnless ssytem ie. a gt500 system, a dual bap, wire upgrades, rail/line/fitting/filter upgrades and pump upgrades, in the end its really a wash cost wise. The return system already has all this stuff from the get go. It has larger rail, larger lines a high flow filter, a return hat that has no pprv valve and pumps that flow much more since they are run at a constant speed, and a wire controller with adequate wiring. Even a bare bones stage 1 or 2, dual pump return kit will support 800-1200hp and your done.
    hockeygod likes this.
  2. hockeygod

    hockeygod forum member

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    Apr 14, 2014
    Rhode island
    Unbelievable explanation. Very well explained. I quite honestly wish I knew that before I went for the dual boost a pumps and gt500 fuel pumps. I already have all of my wiring upgraded and connected to relays and my battery is in the trunk so the connection is very short as well. I would still have a lot to upgrade though it seems vs just parting out the gt500 pumps and boost a pumps and purchasing a return less system. I may have to settle for the 7-750hp range or less for now until I can afford to upgrade the fuel system further.
  3. travelers

    travelers Senior Member

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    Apr 6, 2007
    Eastern Pa
    Not sure, I got the whole upgrade package, C-clip eliminator, 31spline axels with the reluctor rings, with brackets for stock calipers. No mix or fuss.

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