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  1. #1

    Fuel setup and tuning

    I have an 02 w/ a built engine and paxton. The fuel setup is the 2 external pumps and the FMU, along with some type of aftermarket billet fuel rails and injectors. The dyno graph I have shows a "proper" 700rwhp curve (i.e., visually it looks fine).

    Can I remove the external pumps and FMU and put in an RSI double hanger setup and regulator, but leave the current injectors (unknown sizing) and tune alone? It looks like it has a VEC2 (?3?) but nobody here knows how to tune it and with Roe out of business I don't think I can buy the cables and software.

    I was studying the wiring and it looks like they spliced the VEC into the main harness (I have loose wires hanging out all over the place ... but the car works .....). If it has to be tuned, any thoughts on if it'd be easier to unwire the harness/remove VEC and use HP Tuners/SCT to tune the ECU, or just remove the factory ecu/harness/VEC completely and install a Motec?

    Or maybe I should just leave everything as is? It's worked fine for the last 10yrs but when I read about the FMU concept I just don't like it (plus I have some driveability gremlins with it that I think are fuel/tune related)

  2. #2
    Does your dyno show a/f info?

    If your new setup puts the same amount of fuel into the rails at the same pressure level as your old setup, sure it wouldn’t know the difference.

    But that’s exactly why most people change over like you are talking about… the Paxton setup has some room for improvement and if you want to optimize that new twin pump setup (with the other usual mods like larger lines and FPR), you will need to retune it.

    If you can’t find someone that can tune the vec unit than you are left with the other options you mentioned. I started with SCT on my car but moved to HPT a while back (GEN3) and don’t have any complaints. Nothing wrong with the SCT setup, if that’s what your tuner is more comfortable with. If you really want to push that built engine and open up some other possibilities you can explore the Motec setup. However, that tuneability comes at a substantial cost when compared to the other two options…

    We’re it my car, I’d remove the Paxton fuel setup, upgrade to the RSI stuff (I currently have their fuel system myself), and snag a MPVI2 (again, what I have on my g3). Last I knew, the MPVI3 didn’t work with our PCMs (yet?) so you will have to find the previous version currently.
    2006 SRT-10

  3. #3
    The dyno graph doesn't show the a/f so I'm kinda guessing that it's okay based on comparing it other paxton graphs online, and that the previous owner didn't blow it up in 10yrs (which I know is really bad logic, but all I got at the moment)

    I think the path you describe is the best option, my concern is it looks like the VEC has been spliced in to the main harness and I've already got loose wires hanging out of the main harness (i.e., literally hanging out in the engine bay going nowhere)

  4. #4
    Yeah gonna have to rewrite it back to stock before you do much of anything. Shouldn’t be too difficult though in the grand scheme.

    Would be a good project to knock out while you send out the injectors to get cleaned / flow tested so you know what you are dealing with.
    2006 SRT-10

  5. #5
    Not too difficult until you see a load of wires just hanging out in the middle of the main harness not connected to everything (but everything still works, lol)

    Ahhh, the fun of buying somebody elses project ... can never be 100% sure of what was done.

  6. #6
    Tech Team
    Dan Cragin's Avatar
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    I worked with Paxton on these kits and have prepared them in many variations. You want your air fuel in the 11's with steady fuel pressure at peak.

    The stock Paxton fuel setup will support up to 700rwhp with just a pump booster. After that you really need to upgrade the whole system.
    You can easily scale the fueling for the bigger injectors with SCT or the the split second timing controller, if still installed.

    The RSI triple hanger pump module has no surge tank, so you cant run lower than half a tank of gas or there is pressure loss in corners.
    Best setup is to use the stock pump module as a sump with a external pump.
    specialtyperformanceteam.com
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  7. #7
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    I've got a Gen 4 module in my Gen 2. It has the surge tank. Dan Lesser claimed it was good for 700 hp.
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  8. #8
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    Dan Cragin's Avatar
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    Dave,
    That Gen 4 module is perfect pump for more power. I had used them on the Gen 3's that needed an upgrade.

    The Gen 4-5 module is not a direct fit, so it needs to be modified for a Gen 2.

    If Dan Lesser does this modification, he should chime in, as its a good option for earlier cars.
    specialtyperformanceteam.com
    310-597-6295

  9. #9
    Say I wanted to run an external pump like a Weldon 1100a (I use them in all my builds) .... does anybody make a fuel pickup/return for a Viper (i.e., basically 2 -8 fittings welded on to 2 pipes that go to the bottom of the tank)

  10. #10
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    Correct. The Gen 4 fuel module in a Gen 2 is not a direct drop in. But the difficult part to change - basic fitment to the tank - is not an issue.

    Basic compatibilities:

    * mates correctly at the tank opening
    * electrical connection is identical
    * fuel line connection is identical

    Detailed incompatibilities:

    * there is about one inch difference in the height of the G2 tank vs the G4 module with the module being the shorter of the two.
    * the fuel sender arm and resistance module must be changed.

    The module height was changed with the addition of machined spacers to add to the height of the module.

    I sent Dan an old fuel tank that I cut the left and right sides off of so that he could fabricate the float arm. He reused the resistance module off of my old fuel module which I believe was a Gen 3 assembly.

    Anyone interested in this work should contact Dan Lesser for details.

    Spacers:

    Picture 086.jpg

    Installed in G2 car:

    Picture 100.jpg
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    [---T-- L -OlllllllO-]
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