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Thread: Hello everyone. 81 GMC Owner/lover

  1. #1
    Carb and Points!
    Join Date
    Jun 2015
    Salt Lake City, Ut

    Hello everyone. 81 GMC Owner/lover

    Hello everyone, I am glad to be here. After a lot of searching I think this is the place to be. I am rebuilding (slowly) a 5.7 liter SBC engine for my aging GMC as part of an ongoing labor of love. Many years ago I saw an 81 GMC 4x4 in used lot and immediately knew this was the truck I wanted, so I sold the truck I had and bought my baby. Over the years I have done improvements and always wanted to do more but the one thing I really wanted to do but never did due to cost and not knowing how, was to upgrade to a TBI. I had done a little research and figured it wasn't super hard but never committed, partly since I wanted a new engine with it. Well, now I'm committed and have a plan. This is my planned engine build:

    -88 5.7 liter Chevy short block lightly used with a measured CR of 9.3 to 1 using a 64cc heads
    -Promaxx 185cc Vortec heads 64cc chamber with 2.02 and 1.6 valves with 5.75 capable springs
    -Chevy performance hydraulic roller lifers
    -JEGS 1.5 CnC roller rocker arms
    -Comp XR258HR cam (still not sure of this)
    -*dual plane vortec intake manifold
    -TBI to carb adapter plate
    -*TBI power plate PP-200 (R.V.Morse Machine)
    -*Bored 2" TB (R.V.Morse Machine)
    I will probably use short headers, and 2.5 inch dual exhaust.

    My truck has a Turbo 350 transmission with 3.42 axles and a transfer case NP208 (I think). I have a Delco re-manufactured computer module SVC #: 01227747
    I want this build to be capable of being a daily driver and hauling and pulling as needed, which is seldom, but I also want a little something extra. I have read similar builds on this forum and will continue to read to refine my understanding.
    My primary questions which I am researching here are:
    how much cam can a TBI handle and still idle well (of course I will need to have a chip programmed correctly)?
    And, do I need a bored TBI to handle this build?

    I am by no means stuck on this current build idea, that's why I'm here, I think the people here know much more than I do and would love some feedback. If I missed anything let me know.
    I know it’s a long “Hello” but I thought I would get the basics covered.
    Last edited by jdbrown; 06-30-2015 at 07:47 AM.

  2. #2
    Fuel Injected! Roadknee's Avatar
    Join Date
    Dec 2013
    North Central Washington
    Welcome. Nice to meet another one of us with passion to keep these old trucks alive.

    Going through the effort to convert to TBI, I'd recommend you upgrade to the later model 7427 PCM. It has many more capabilities than the 7747 and can run a 4L60E or 4L80E down the road if you desire.

    The cam you selected will be fine. It should pull strong to 5,000-5,200 rpm and be relatively easy to tune. You could go bigger, but with your desire to tow and just have something a little extra it will work well.

    You won't need a bored TB. Yes, it would produce a little more power (5-8 hp peak) at WOT above 5,000rpm. I think you could just perform the ultimate TBI mods to a stocker and be fine.

    The heads are larger than you need for a truck build. Below 5,000 rpm a smaller head would pull stronger like the Edelbrock E-tec 170's or EngineQuest Vortecs.

    For a daily driver, I prefer an intake manifold with a water heated plenum like OEM. You can get the EQ Vortec heads with the proper intake flange to use the stock manifold. The plus with the stock manifold is it has all the provisions in place for the various brackets and sensors. If you want the Vortec flange heads, you can use the GMPP intake, Crusader marine intake or Edelbrock perf RPM, which all have provisions for a heated plenum.

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