quick carb swap question
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Junior Member
Joined: Oct 2011
Posts: 61
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From: San Diego(now)/ Springfield, Oh(orig)
Car: 1991 firebird XS
Engine: 5.7 tbi
Transmission: stock 700r4
Axle/Gears: 9 bolt 3.23
quick carb swap question
I know all parts and labor required, I'm not looking for a bunch of answers, just one...I'm wanting to put a 4bbl on my tbi car but I want to keep my tbi harness and elect Speedo so can I just connect into the tach wire and go that route? I would like to keep tbi stuff for when I have to smog the car...
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Supreme Member
Joined: Sep 1999
Posts: 7,072
Likes: 13
From: Philly, PA
Re: quick carb swap question
Yes, you absolutely can do that, if you don't mind swapping intakes to do the change-over each time. I left the ECM and complete wiring harness untouched on my 92 Camaro when I swapped to carb, just in case I ever wanted to swap it back to TBI.
Now, you're going to need an earlier non-computer controlled HEI distributor and that uses different connections for the tach and coil power than your later divorced-coil computer controlled setup. So when you swap back and forth you're going to need something to swap back and forth between the earlier (spade connector) HEI connections and the later (2-wire coil connector) divorced-coil connections. But that should be easy if you keep the old coil connector with a few inches of wiring still attached to it when you clip it off- just put some male spade connectors on the ends of those wires and you can plug them back into the female spade connectors you will have on the other end to connect to the earlier-style HEI distributor. Does that make sense?
Now, you're going to need an earlier non-computer controlled HEI distributor and that uses different connections for the tach and coil power than your later divorced-coil computer controlled setup. So when you swap back and forth you're going to need something to swap back and forth between the earlier (spade connector) HEI connections and the later (2-wire coil connector) divorced-coil connections. But that should be easy if you keep the old coil connector with a few inches of wiring still attached to it when you clip it off- just put some male spade connectors on the ends of those wires and you can plug them back into the female spade connectors you will have on the other end to connect to the earlier-style HEI distributor. Does that make sense?
Thread Starter
Junior Member
Joined: Oct 2011
Posts: 61
Likes: 0
From: San Diego(now)/ Springfield, Oh(orig)
Car: 1991 firebird XS
Engine: 5.7 tbi
Transmission: stock 700r4
Axle/Gears: 9 bolt 3.23
Re: quick carb swap question
yes, that does make sense, i am mostly concerned about if i switch to carb will my electric speedo still work correctly? if i get an official yes, then when i get back from deployment the bird is getting a carb conversion because i cant find anyone around that tunes tbi engines
Supreme Member
Joined: Sep 1999
Posts: 7,072
Likes: 13
From: Philly, PA
Re: quick carb swap question
Yes, the speedo will definitely work if you leave the ECM in place and hooked up (just pull the Check Engine bulb so it's not lit up all the time and burning your retinas out at night). I did a carb conversion personally on my 91 RS with original 305 TBI. Every single factory dash gague still worked. Only thing that wouldn't was the torque converter lockup function (for which they sell kits to lock it up without using the ECM).
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