LS1 Fuel pump swap into 2nd gen tank

Discussion in 'High Tech Retrofits' started by anesthes, Nov 23, 2011.

  1. anesthes

    anesthes Veteran Member Lifetime Gold Member

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    This assumes you have a 76-81 Camaro/Firebird with the (I think) taller fuel tank.

    Start with a stock fuel tank. You want to cut out the 6" circle where the vent assembly is. (circled in red). This is where you will eventually mount the new fuel pump. Below this 6" circle is another "pot" of sorts, designed to be a barrier between the fuel to allow venting without fuel spill. You will want to cut that out as well.

    [​IMG]

    So once you have that cut out, you want to get a nice flat piece of steel sheet, roughly 20 gauge. I cut this out of another fuel tank that had a nice flat surface. You want to cut this out exactly 6" round and weld it in place. Grind your welds down flush.

    Now you have a nice flat surface for the fuel pump gasket to rest.

    Next, you want to cut a 3.875" circle in the dead center of this 6" area. I used a compass to draw a circle then cut it out with my air saw. It's not perfectly round, but it doesn't matter. As long as enough lip exists for the pump gasket you will be golden.

    So then take your vette works adapter, and lay the studded part into the 6 inch area perfectly centered. The outside is pretty much dead on 6" so this won't be hard, and weld it in place:

    [​IMG]


    I then ground the welds down, and sealed it over with some permetex metal filler which was gasoline and oil safe, then I primed and painted the tank with textured black:

    [​IMG]


    So now your tank is modified. You can use LS1 fuel sender by modifying the resistors in your fuel gauge, but I decided instead to just use the factory sender since I needed to plug that hole anyhow. I cut the bottom of the pickup off, so the sender is just foe fuel level information. You can plug the top two lines.


    Next you need a LS1 fuel pump assembly. 99-02 is what you want, for cars with PLASTIC fuel tanks. I swapped the pump inside my assembly with a 255lph fuel pump, however for under 450hp applications the stock pump will be just fine:

    [​IMG]

    I purchased all my fuel fittings from Summit, however you can buy them from Vetteworks as well. I'm running the same loop pictured above, so that I can use the built in fuel pressure regulator in the module, which is factory set at 58psi. This allows me to run a single fuel supply and NO RETURN LINE.

    The middle fitting can be used as a vent connection, or if you choose to run a regulator at the fuel rail use the middle connection as a RETURN.

    If you are using the middle as a return connection, make sure you use one of the original fuel lines (the 1/4" should be fine) cut high as a tank vent.


    OK here is a completed tank. It is a little tight where the fuel fittings go, so I added some foam (universal weatherstrip) on the mount areas. This is the location that appears to work best.

    In the pic, I've kept the 1/4" line for a vent on the factory sender. The factory sender will operate the fuel gauge as normal. On the new LS1 pump, the right fitting (black) is pressure, it's a 3/8" GM quick connect to -6AN. The middle is a 5/16" GM quick connect to -6an and factory for a tank vent, it's a spring loaded open connection that can be used as a return if you wish to use a rail mounted regulator. The left most is a 3/8" GM quick connect to -6AN and it goes into the factory regulator in the pump module, which regulates pressure at 58PSI from BARO.


    [​IMG]


    With this combination, I'm guaranteed to always have a full bucket of fuel (the module is a bucket) as return fuel is kept in the bucket, so no amount of hard braking or cornering will run me out of fuel and stall the engine.

    -- Joe
     
    Last edited: Nov 25, 2011
  2. POS71RS

    POS71RS Moderator Staff Member Lifetime Gold Member

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    Awesome!
     
  3. reedld

    reedld Veteran Member

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    Nice!!!!!...I put off doing this exact process to my tank earlier this year. I have all the parts except I want to buy a new tank...kinda scared to cut into a tank that had fuel in it. Real happy to see someone else do it too! Have you run it much? My ride is put up for the season. Thanks again and please reply with any news/feedback.
     
  4. anesthes

    anesthes Veteran Member Lifetime Gold Member

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    Have not run it. Just finished this tank. I drained it a while back. It's been sitting in the shop with the sender out for months. I blew compressed air in it for a while. No fumes. So I just went at it. No explosions. :)

    -- Joe
     
  5. mrvedit

    mrvedit Veteran Member

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    Great write up! I also have all the parts (GM fuel bucket and Vetteworks kit) and plan to buy a new stock tank from NPD. I'm currently running an external Walbro 255 pump with return line.

    However, I don't understand this part:

    "So once you have that cut out, you want to get a nice flat piece of steel sheet, roughly 20 gauge. I cut this out of another fuel tank that had a nice flat surface. You want to cut this out exactly 6" round and weld it in place. Grind your welds down flush."

    I thought that was the purpose of the Vetteworks kit. ???

    As many people recommend on ls1tech, I will continue running with a return line so that I don't have to tune to compensate with some pressure drop during WOT.

    Also, what pump did you use? A Walbro GSS342?
     
  6. DoTheDew

    DoTheDew Veteran Member

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    Sticky
     
  7. anesthes

    anesthes Veteran Member Lifetime Gold Member

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    So if you look at the area I circled, you have a vent assembly in the tank that is offset. If you try cutting that offset circle out and putting the flange there the pump won't quite fit. The pump really needs to go in the dead center of the larger circle.

    That vent has a small line that does a 90 degree bend out of this weird bowl that is inside there. So I cut the whole 6" circle out, and replaced it with a nice fresh flat plate. I then centered my new hole for the fuel pump, and welded the vetteworks flange to that.

    IF the fuel tank was flat, and I mean FLAT FLAT so the pump gasket would seal, in an area that gave you enough depth to run a full height LS1 fuel pump than all you would need to do is cut a 3.875" hole like on the Corvette. However, since that stupid vent assembly is there, you need to cut it out, and once you cut it out, you have a hole in the wrong spot as the tank begins to slant directly under that offset hole.

    Also, you don't want the float of the gauge sender to crash into your new LS1 bucket.


    I used this pump from TRE performance:

    http://www.ebay.com/itm/280598322557?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

    It has the appropriate pressure feed for the venturi. Walbro does not recommend removing a top screw and running a fitting/hose in that location to pressurize the venturi with their pumps.

    As far as pressure drop goes, you actually won't drop pressure at WOT. What happens is the pressure differential changes due to the fact that the pressure in the intake goes from vac (11-22hg) to almost zero. This is why the engineers added a vac referenced regulator, I'm guessing so a smaller injector could be used vs a varried pulsewidth. I don't see how I'd notice the difference while tuning though, I mean, wideband reported AFR is what it is. My fuel table is map (RPM vs kpa). If you aready have a tuned fuel map however, you'll want to keep the vac referenced FPR.

    -- Joe
     
    Last edited: Nov 23, 2011
  8. anesthes

    anesthes Veteran Member Lifetime Gold Member

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    There might be some confusion about the vetteworks adapter.

    The part with the studs is intended to be welded to the top of the fuel tank on a flat surface. On that surface, you need a 3.875" hole so the fuel pump fits in, but the flange on the pump rests on that surface (with a gasket under it). Then the other ring vetteworks supplies goes over the top of the fuel pump flange, and is tightened down.

    What vetteworks SHOULD have done, was make the inside hole on the studded ring the appropriate size to fit the pump, rather than it being WAY oversize. Or simply, have another plate welded under it. Most fuel tanks do not have a nice flat surface on the top, most are ribbed in some fashion so you end up having to cut and weld on the tank long before you can even use the vetteworks adapter.

    -- Joe
     
  9. mrvedit

    mrvedit Veteran Member

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    Thanks for the explanation. I still don't fully understand it, but hopefully will when I start the work.

    Yes, GM designed the fuel system for rear regulation and tuned the computer accordingly with a vacuum reference. Personally I think it is a cost safer and works "well enough". From what I read on ls1tech, many consider regulating at the rails a worthwhile improvement. I'm already set up that way.

    Thanks to your helpful info, I now feel comfortable doing this with a new tank.
     
  10. 1971CamaroGuy

    1971CamaroGuy LS Swapped 1971 Camaro

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    Have you tried to mount the tank with the pump in it yet?...does it hit the floor? Just curious if the floor is going to cause fuel line routing and getting the tank to mount properly
     

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