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Thread: First attempt at carb to GM TBI conversion - am I in over my head?

  1. #1
    Fuel Injected!
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    Question First attempt at carb to GM TBI conversion - am I in over my head?

    Hi, GearHeads,
    I have hopes of using a donor 1989 Chevy V8 305 TBI system on a 1969 Chevy L6 292. Probably someone has done it already, and can steer me through the process. I have, as one poster put it, "stuffed the guts" of a 7 wire (coil on cap) distributor into the base of a distributor from a 250 L6, and done away with the 250 distributor's advance systems. I also have a 6 wire distributor from a 1993 4.3 V6, and I like the smaller distributor with the external coil, which I could possibly graft on to the base of the original distributor. The 292 is presently running with the big base vacuum/centrifugal advance HEI distributor with an external coil. Which is the best (simplest) route?
    The 292 presently has a spread bore QuadraJet on an adapter plate on an Offenhauser standard bore four barrel intake. The adapter is undivided for the barrels, but the manifold and its carb mounting plate have the four barrels. So if the TBI adapter plate (presently partly made) is mounted/centered on the Offy manifold, it will feed on to the divisions between its four barrels. Is that a problem? Most pictures of TBI adapters show one oval opening, not two round ones like TBI manifolds use. Is there an advantage either way? Sometimes I remember Sgt. Shultz saying, "I know nnnnnothing!", and identify with him.
    The PCM from the 305 is 1228746, APFN. What number PROM do I need, and where do I find it - on a 4.3?

  2. #2
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    Welcome to the forum.

    If you have a modified HEI distributor that is essentially set up for computer control, that seems the best way to integrate spark control.

    Optimum fuel delivery to the cylinders will suffer some if the fuel droplets are allowed to hit the adapter. Will you notice it? Possibly not.

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