350 TBI to 400 carb swap


LawnSite Member
I have an '87 chevy 4x4. I am taking the 350 and TBI out and putting in a very built 400sb with a carb. My question is will I have to change any wiring harnesses to an older style. As far as I know the computer only controls the injectors and o2 sensors. If I just unhook the computer it shouldn't effect anything in the dash or prevent the truck from starting with the new motor correct? I already know that I will have to change the gas tank floats and maybe fuel lines and flexplate. Any help on the wiring issue would help me out a lot. I would really appreciate it. Thanks.


LawnSite Senior Member
I took the computer out of my truck (83 V8) and here's what I had to do. I got a different distributer so that I wouldnt' have to mess with the knock sensors that work with the electronic spark control. I also had to get a vacuum sensor that actuates the lockup on the torque converter for the TH700r4. It also comes with the wiring harness that clips right in to the top of the tranny case. Other than that, the starter and ignition hooked right up. I assume that if you went with a HEI distributer from the parts store for a 70's small block that it would all work. Good luck.


LawnSite Member
Your '83 didn't have a "computer" like TracStr400 does. His runs his TBI. Your truck had an ESC, which only controlled your spark. It is junk and usually dies only to leave you stranded.

Your computer gets feedback from the water temp sensor, knock sensor, TPS, O2 and IAC. I controls your distributor, tranny lockup and the injectors based on these sensors. If you plan to ditch the computer, you will need a new distributor (pre-ECS) and a switch for lockup on the tranny if you have the Overdrive. The truck should crank and run without the computer plugged in, especially if you are ditching the Electronic stuff. I can't remember exactly how it interfaces with the rest of the wiring, but I think it might just be the guages.

When you strip the computer/harness out, can I have it? <grin>

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