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Thread: 7747 TBI Tuning: where to next?

  1. #1
    Carb and Points!
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    7747 TBI Tuning: where to next?

    Hey All,
    Before I start, truck is a 1990 4x4 GMC Jimmy with TBI, 350, 700r4, NP241, 33" tires, 4" lift.

    Current bin and logs are attached, using the $42-1227747-V5.9.3.xdf and $42-1227747-V5.2.adx

    Been working on tuning my stock TBI as a way to learn the ropes, in about a month I will be pouring about $5K into the motor and want to be up on tuning for it before I do. I have a good ALDL cable, an Ostrich 2.0, and a MiniPRO EEPROM writer.

    My motor is stock, worn out, the only things I have done are the normal tune up steps(new plugs, new wires, new dist cap, new air cleaner, regular oil changes) flip the lid on the air cleaner, and installed a AcDelco EP381 pump. Still running the stock regulator.

    So, right now I am running the ASDU base tune with VE tuning done(using the spreadsheet). Looking at my data logs I have a few questions on where to go from here.

    One: I was going to throw more timing at it but going by the knock counts I think the stock timing curve is about right, but curious on others thoughts(I.E. is the 200+ knock counts OK?)
    Two: The Injector Duty Cycle approaches 100% under WOT sometimes, so do I need to raise my fuel pressure to get more fuel going in, or am I reading too much into it?

    Overall the VE changes were minor, the biggest change I have done is enabling HiWay Lean Cruise Mode, which will pay for the Ostrich on its own with my improved MPG(I drive a LOT!)


    Thanks in advance!
    Scoutcamper
    Attached Files Attached Files

  2. #2
    Fuel Injected! CDeeZ's Avatar
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    If you're getting ready to dump 5 grand into an engine I would reccommend repinning your harness and switching to a 7427.

    Lots of people tune by BLM but I prefer using a WBO2, ESPECIALLY for a performance engine like you're talking about. The 7427 has a lot of support, and is a much faster and better computer. Can the 747 do the job? Absolutely. The 7427 is IMO a better alternative. It is faster. It can control E fans and transmissions. You can hook a WBO2 into the data-stream to make tuning easier. It has two 3D fuel tables instead of the smaller main table plus the 2D adder table that the 747 usues.

    You can use BLM to adjust fuel but I would encourage you to get a wideband. It will make dialing it in easier. IMO this is even more so when you're talking about building an engine like you are.

    Don't worry about the timing tables until you get everything else dialed in, then revisit them. You can bust a ringland with knock if you're not careful. Especially true with boost.

    I like 85% max duty cycle. Once you build that engine you will almost certainly need more injector and/or fuel pressure.

  3. #3
    Carb and Points!
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    Quote Originally Posted by CDeeZ View Post
    If you're getting ready to dump 5 grand into an engine I would reccommend repinning your harness and switching to a 7427.

    Lots of people tune by BLM but I prefer using a WBO2, ESPECIALLY for a performance engine like you're talking about. The 7427 has a lot of support, and is a much faster and better computer. Can the 747 do the job? Absolutely. The 7427 is IMO a better alternative. It is faster. It can control E fans and transmissions. You can hook a WBO2 into the data-stream to make tuning easier. It has two 3D fuel tables instead of the smaller main table plus the 2D adder table that the 747 usues.
    I like this idea, my $ amount was off a bit(included trans, exhaust, and some extra supporting parts not going into the engine), my actual build is planned to be as follows:
    Summit Pistons SUM-17350C-00
    Summit Heads SUM-162108
    New Crank and Rods
    Cost for bottom end rebuild
    RVMorseMachine Ported TBI
    Port existing Intake Manifold
    Comp Cams 08-501-8
    1.6:1 Roller Rockers

    Should end up with 300-ish hp and 450-ish tq at the crank. 10:1 compression ratio.

    I am planning to go to E-Fans at some point soon so that makes me happy, Im planning to stick with the 700r4 so i wont use the trans tuning anytime soon.

    With that in mind would you still go with the 7427? my only hesitation on swapping is that right now I have a good base tune for the 7747, but with such a drastic change I suppose it doesnt matter much.... I am in CA so I am picking parts that are smog legal where possible, though the computer should not matter. Thoughts?

    You can use BLM to adjust fuel but I would encourage you to get a wideband. It will make dialing it in easier. IMO this is even more so when you're talking about building an engine like you are.

    Don't worry about the timing tables until you get everything else dialed in, then revisit them. You can bust a ringland with knock if you're not careful. Especially true with boost.
    Makes sense, I wish I was going boost, but not this go around

    I like 85% max duty cycle. Once you build that engine you will almost certainly need more injector and/or fuel pressure.
    Makes sense, I have no problem bumping the fuel pressure, just need an AFPR or one of the springs for more pressure.
    Last edited by scoutcamper; 03-16-2018 at 07:19 PM.
    1990 White/Blue GMC Jimmy
    350 TBI
    700r4
    33" Tires
    4" lift

  4. #4
    Super Moderator dave w's Avatar
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    See attached screen shots using Wide Band Tuning with a '7427 PCM: http://www.gearhead-efi.com/Fuel-Inj...g)-Spreadsheet
    Attached Images Attached Images

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