70NE's custom EFI conversion writeup - Part 2

Discussion in 'Classic Mustang Specific Tech' started by ForceFed70, Jan 4, 2006.


  1. ForceFed70

    ForceFed70 That's why they call it "dope" Founding Member

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    Hello everyone,

    For part 1 of this writeup, go here: http://forums.stangnet.com/showthread.php?t=593406 it will explain alot about the custom EFI system I chose to use (MegaSquirt) and my goals.

    I got the car started today using the new EFI system! :cheers: :cheers: I still need to do alot of tuning, but everything looks like it's working the way it's supposed to.

    Which got me thinking... I'm way behind in my updates! So anyway... her's Part #2.. and it's all about the fuel system.
    #1
  2. ForceFed70

    ForceFed70 That's why they call it "dope" Founding Member

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    Part 2 – Fuel System

    An EFI conversion on a classic car requires a regulated, high-pressure fuel source. Which means a whole new fuel system. Because I chose to use a Throttle Body Injection (TBI) system I’ll need a fuel pressure of approx 15-20 PSI. If I had chosen port injection, then I would have had to use higher pressure fuel injectors and run the fuel pressure at 35-40PSI. Because of the lower pressure of the TBI system there are a few more options available for fuel lines and connectors.

    Fuel Tank:
    Factory EFI vehicles have baffles in the fuel tanks to make sure that on hard cornering the fuel pump doesn’t end up sucking air into the fuel system. This is usually more of a problem when the fuel level is low. In a carbed vehicle, this isn’t a problem as it’ll “burp” through the carburetor.
    I’ve chosen not to install a baffle at this point. Mostly because I’ve been told that this really isn’t a problem until you get below ¼ tank. Since this is a weekend car, I don’t see that being a big concern. For now I’m going to try it without and see what happens. If it turns out to be a problem I’ll investigate installing baffles, or perhaps a surge tank.
    #2
  3. ForceFed70

    ForceFed70 That's why they call it "dope" Founding Member

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    Fuel Return and Pickup:
    Because a regulated fuel pressure system needs a return line, you must run a return line from the fuel pressure regulator back to the tank. In most cases this means a 2nd fuel line all the way from the engine to the fuel tank.
    There are a few different options for attaching a return line to your fuel tank. The easiest would probably be to use the drain plug. Unfortunately my fuel tank was not fitted with a drain plug. The other easy option is to tap into the fuel tank’s rubber filler neck. However, for the cleanest look without too much effort, I decided to modify my fuel level sender.
    [​IMG]
    As you can see by the picture, I drilled a hole in the fuel level sender’s plate and then had a fitting brazed on by a local shop. Apparently I made a poor choice in fitting materials as brass and steel are apparently very hard to braze… hence the “booger” welding by the shop. A steel connector would have been much easier to weld and the welds probably would have looked a lot cleaner. However…it’s effective and doesn’t leak, so that’s all that matters in this case
    [​IMG]

    Attached Files:

    #3
  4. ForceFed70

    ForceFed70 That's why they call it "dope" Founding Member

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    Here’s the fuel level sender from a different angle.
    [​IMG]

    Attached Files:

    #4
  5. ForceFed70

    ForceFed70 That's why they call it "dope" Founding Member

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    The fitting I used was a 3/8th’s NPT to 3/8ths hose barb. The red line shows where I cut the threaded portion of the fitting off to leave only the barbed portion. Again, apparently steel is a better choice than brass for ease of welding.

    [​IMG]

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    #5
  6. ForceFed70

    ForceFed70 That's why they call it "dope" Founding Member

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    Here’s a picture of the fuel sender mounted back on the tank along with the lines and pre-filter. At this point, neither of the fuel lines will see high pressure and you can use regular low pressure hose. The supply line is low pressure because this is all before the pump, and the return line feeds directly to the tank so it’s also low pressure. For best performance you want to mount the pre-pump filter and fuel lines as low as possible. The location I used should be fine, but mounting a few inches lower would be ideal.
    [​IMG]

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    #6
  7. ForceFed70

    ForceFed70 That's why they call it "dope" Founding Member

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    Fuel Line:
    Routing the fuel line was straightforward. I mostly followed the same path as the stock line. Here is a picture of the fuel line and fittings I used. See part 1 for more information on this line.
    [​IMG]
    #7
  8. ForceFed70

    ForceFed70 That's why they call it "dope" Founding Member

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    Fuel Pump:
    I chose this location to mount the fuel pump mostly because it was low (the lower the better) and I already had holes and mounting hardware in the frame rails from a removed anti-sway bar (victim of lowering). From the pump to the fuel pressure regulator you will have to use a fuel line capable of handling the higher fuel pressure.

    [​IMG]

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    #8
  9. ForceFed70

    ForceFed70 That's why they call it "dope" Founding Member

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    Fuel Pressure Regulator and Injectors

    Using throttle body injection is nice because you cram a bunch of different EFI components into a single package. The Holley TBI I purchased has the throttle plate, the Throttle Position Sensor, the fuel pressure regulator, fuel rails, fuel injectors, and idle air control all built into a single unit. Installing the TBI unit is much the same as installing a carburetor.

    In this picture you can see the fuel lines enter the throttle body. The high pressure filter is hidden under the export brace. You’ll also notice the fuel pressure gage that I mounted directly to the throttle body using a plugged port that was created during the throttle body machining process. The air cleaner wraps around the gage perfectly, but you must remove the air cleaner base to read the gage.
    [​IMG]

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    #9
  10. ForceFed70

    ForceFed70 That's why they call it "dope" Founding Member

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    OK, that's the end of Part 2.

    Part 3 (Electrical) will be the next in the serries and should come soon now that I have the car running.
    #10
  11. bnickel

    bnickel Founding Member

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    sweet bro, looking forward to more pics and the rest of the series as well. do you think you could post some pics of the unit from the front of the engine with and without the air cleaner in place? i'm curious to see just how stealthy this is going to be
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  12. 10secgoal

    10secgoal Active Member

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    Could always run a return system. Easier on the pump, and quieter.

    Looks great. thought about this route for my car.:hail2:
    #12
  13. ForceFed70

    ForceFed70 That's why they call it "dope" Founding Member

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    Sorry, do you mean a returnless system? I wasn't even aware that an aftermarket system was available. Is there something out there that regulates fuel pressure by varying voltage to the fuel pump? That would be ideal if it was reliable and not too expensive.
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  14. ForceFed70

    ForceFed70 That's why they call it "dope" Founding Member

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    I'm not quite done with it yet, but I'll make sure to include those pics in my next update as at that point the hardware installation should be complete. Then comes the tuning.
    #14
  15. red65

    red65 Member

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    Very nice, well thought-out project. Post an update on how it runs, too!
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  16. 10secgoal

    10secgoal Active Member

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    You might be able to run a regulator that would vary psi for you if you wanted. I meant a return for the fuel only. You can actually use any regulator in a return system. Just set it up a little different. I was suggesting that mybe it would work, and have other benefits rather than baffling the tank.
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  17. bnickel

    bnickel Founding Member

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    are you talking about a closed loop return system? where the return fuel is routed back to the pump instead of the tank? that would work well for what he is doing although i'm not sure if the pressures of the EFI system will effect it. i see this type of return system used on carb'd cars all the time and it works quite well in that app.
    #17
  18. 68converted

    68converted Member

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    I have some interest in the idea of having the return fuel line feed into the line running from the tank to the fuel pump. Kind of a backward dump system. Would that actually work? Any issues with doing such a system return/feed?
    #18
  19. ForceFed70

    ForceFed70 That's why they call it "dope" Founding Member

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    The main concern is air in the fuel lines. We need a way of getting as much of this air out as possible without the air going through the injectors. Even with baffles in the tank you will run into instances when air is sucked into the system (Bubbles,sloshing, low tank, hard launch, etc).

    A carb can "burp" the air out through the floats. But the only way to "burp" an EFI system is back into the fuel tank.

    This means there must be a path the air can travel all the way back to the tank.

    What you describe here is 1/2 of a "surge tank" setup. Check out this webpage for a great description of what a surge tank is and does. http://toyotaperformance.com/surge_tank.htm
    #19
  20. ForceFed70

    ForceFed70 That's why they call it "dope" Founding Member

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    The system I'm using does have a return fuel line.. but I still expect that the fuel pickup will come uncovered at times(easier to do in an unbaffled tank) and suck up some air . Most of the air will hopefully go back out through the return line, but I still expect some of it to make it's way through the injectors.
    #20

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