Ultimate TBI Mods

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Ultimate TBI Mods

I picked up an 89 Chevy short bed Cheyenne a while back.  I went to look at it because I was looking for a drivetrain for my 56 GMC project.  When I found the truck it was way too straight and in good condition that I couldn’t tear it apart.  To get it running all it needed was a new battery and fuel pump.

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The owner gave me receipts from the dealer that showed a crate 350 was put in the truck about seven years prior.  Looking at the TBI I wondered if they even cleaned it off before reinstalling it!  It was filthy!  I had modified the TBI in a 1989 Dodge with the Magnum 360 with good results and had read about people having success with the same type of mods on 88-98 Chevy truck TBI’s.

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It really doesn’t take much to pull the TBI out.  I did what many people call a Stage 1 modification.  Basically the ridges surrounding the intakes are removed and the openings are widened and smoothed.  As you can tell from the pictures, I wasn’t too worried about getting a mirror finish on the surfaces.  For one, it’s in an area that will never be seen and second, it is thought having too smooth of a surface in this area actually decreases performance.

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Some people will also grind down the butterfly shafts but I wasn’t really interested in taking this modification to that level.  It took about an afternoon of kick back working to removed, clean, modify, and reinstall the TBI.

It’s hard to objectively say what the results were because I made other significant changes at the same time that directly affected performance.  I had just put in a rear axle changing my gearing from 3.09 to 3.43.  Also, the TBI was completely covered in gunk and I’m sure some of the increase in performance was due to losing a few layers of dirt and grime.  I also cleaned out the injectors themselves and was getting a much better spray pattern than before.

Regardless of what caused what, the engine itself was much more responsive which is what other people report who have done the mod.