Tbi to carb swap - what wires are and aren't needed?

[NeatEvenin]

Thank you ScooterWrench for the explanation. Thank you to everyone else with chiming in as it has helped me figure out some things that I need to do.yes I'm using the in tank pump, I just didn't know if the codes for the iac, TBI stuff and EGR would throw codes and prevent the fuel pump from giving the carb fuel. My power goals are around 500-600hp naturally aspirated, with forced induction coming in the future. Yes this is my daily driver but this is also my dream truck and I want it customized the way I want.ive got a 700r4 and I know that the only signal I really need was the TV cable for line pressure and stuff. I was honestly thinking of making a custom harness from a separate one from a junked truck if I could find one. Everything works as of right now. I'm definitely going to spend a few hours tonight hiding wires, but undoing everything isn't going to prevent the fuel pump from working?

 

[Scooterwrench]

Your 700R4 gets a signal from the ECM to engage and disengage the TCC which takes inputs from the TPS,MAP and VSS. You WILL have to use some sort of vacumm operated switch to operate that or you WILL burn out the TCC. Whatever carb you are running is going to have to have the throttle lever modified so it has the correct geometry for the TV cable. Get that wrong and you will be constantly building and/or replacing transmissions.

 

[Sean Buick 76]

For the trans lockup simply use a TCI lockup kit which is a vacuum switch. Add the factory brake switch that will shut off the lockup when you tap the brakes ti eliminate stalling.

 

[Schurkey]

For the trans lockup simply use a TCI lockup kit which is a vacuum switch. Add the factory brake switch that will shut off the lockup when you tap the brakes ti eliminate stalling.

That's exactly what I did, when I stuffed a 700 into a '76 Nova. I hated it.

The TCI vacuum switch was a piece of crap. Has no hysteresis, so although it could be "adjusted" for vacuum level, it turned on and off at the same vacuum level, but that vacuum level can be changed.

Which means that the vehicle would speed up, the engine rpm would climb, and at some point it would generate enough vacuum to close the switch--providing the signal to engage the torque converter clutch. The clutch engages, rpm drops, which drops the vacuum, which opens the switch. Which kills the TCC engagement. RPM climbs as does vacuum, switch engages, TCC engages...RPM drops, vacuum drops, switch opens...and this continued until I stab the gas pedal to get way more speed, so that when the TCC engages it still had enough vacuum to keep the TCC engaged.

A proper vacuum switch would be adjustable, but have a different (higher) vacuum level for closing (engagement) and lower vacuum level for opening (disengagement). For example, 15 inches of vacuum to close, only ten inches to open. That way when the TCC engages and vacuum drops, the switch stays closed.

I have no reason to believe that the TCI kit has a better vacuum switch now than it did all those years ago.

 

[Scooterwrench]

That's exactly what I did, when I stuffed a 700 into a '76 Nova. I hated it.

The TCI vacuum switch was a piece of crap. Has no hysteresis, so although it could be "adjusted" for vacuum level, it turned on and off at the same vacuum level, but that vacuum level can be changed.

Which means that the vehicle would speed up, the engine rpm would climb, and at some point it would generate enough vacuum to close the switch--providing the signal to engage the torque converter clutch. The clutch engages, rpm drops, which drops the vacuum, which opens the switch. Which kills the TCC engagement. RPM climbs as does vacuum, switch engages, TCC engages...RPM drops, vacuum drops, switch opens...and this continued until I stab the gas pedal to get way more speed, so that when the TCC engages it still had enough vacuum to keep the TCC engaged.

A proper vacuum switch would be adjustable, but have a different (higher) vacuum level for closing (engagement) and lower vacuum level for opening (disengagement). For example, 15 inches of vacuum to close, only ten inches to open. That way when the TCC engages and vacuum drops, the switch stays closed.

I have no reason to believe that the TCI kit has a better vacuum switch now than it did all those years ago.

I remember you you stating this in another thread about that POS TCI switch. Have you ever tried the factory TCC switch that they used in the early 80's in the CCC systems?

 

[95burban]

If your power goals are 5-600hp na that 700r4 won’t last. If you switch to a TH400 you won’t need to worry about the TV cable and the th400 will handle the power, but you will loose OD. Need to factor in rear end gear, stall rpm and tire size.

 

[Scooterwrench]

According to Nick those trannys can be built to withstand that much HP but it won't be cheap. Another option would be to run a 4L80-E with a trans controller and have the OD for more economical cruising.

 

[Sean Buick 76]

I simply ran a toggle switch in line with the vacuum switch so I could override it when I wanted it to stay off.

The later tci kits are adjustable and feature an override option as well:

https://www.tciauto.com/tci-universal-lock-up-wiring-kit-gm-700r4.html

 

[Sean Buick 76]

I use one of these:

Transmission High Gear Lock up Switch Kit for TH 700-R4 4L60 200-4R K013 74416AK | eBay

Find many great new & used options and get the best deals for Transmission High Gear Lock up Switch Kit for TH 700-R4 4L60 200-4R K013 74416AK at the best online prices at eBay! Free shipping for many products!

www.ebay.ca

 

[Scooterwrench]

I use one of these:

Transmission High Gear Lock up Switch Kit for TH 700-R4 4L60 200-4R K013 74416AK | eBay

Find many great new & used options and get the best deals for Transmission High Gear Lock up Switch Kit for TH 700-R4 4L60 200-4R K013 74416AK at the best online prices at eBay! Free shipping for many products!

www.ebay.ca

That may work for a passenger car but I wouldn't use that in a truck where you may be towing in third.