1997 5.7/4L60e carb conversion help needed

[Don Jordan]

My future son-in-law has a 1997 Tahoe 4x4 with a 5.7L and 4L60e tranny. The spider injection assembly has gone bad, plus the fuel lines that go to it move up and down along with their stud mounts. He's decided he wants to cross it over to carb. I'll be helping him, but I admit that my experience is rather limited when it comes to mods. I understand the transmission is computer controlled and will need certain inputs, but i don't know which ones. Can the computer be used as a stand-alone controller for the tranny?

Also, he wants to completely rebuild the motor and go with a bigger cam. But looking at the specs, is it really possible to go big cam-wise? The lift looks like it will be limited by the guides in the head. Are there practical mods for this?

I haven't turned wrenches in 20+ years. To say I'm rusty would be a major understatement! Any help would be greatly appreciated.

 

[drakon543]

you can definitely upgrade the cam but your lift will definitely be limited. if he is dead set on a big cam comp cams are really helpful and they know thier products. so i would suggest calling them for specifics regarding the cam style he wants. as far as the fi to carb swap he wants to do as far as i know its possible but i dont know the specifics. however as he wants to rebuild the engine anyway why not just get the better spider injectors from rock auto and fix whats there?

 

[Don Jordan]

you can definitely upgrade the cam but your lift will definitely be limited. if he is dead set on a big cam comp cams are really helpful and they know thier products. so i would suggest calling them for specifics regarding the cam style he wants. as far as the fi to carb swap he wants to do as far as i know its possible but i dont know the specifics. however as he wants to rebuild the engine anyway why not just get the better spider injectors from rock auto and fix whats there?

Well, so far I have the exhaust dropped, the radiator is out, and the front of the motor is bare. As I started disconnecting all the electrical connections on the top, some of them are brittle and breaking apart. The spider assembly is totally screwed up. It looks as if someone else has been in there trying to seal off a leak. It's really a mess, and at this point, I don't have much faith in the original upper intake, anyway.

A few more connections, tranny mount bolts and engine mounts and the motor will be ready to put on an engine stand.

 

[drakon543]

i wouldn't be concerned about the lower half and the upper plenum is only 70 bucks on rock auto and the whole spider kit is about 200 bucks. 250 for a decent carb intake and another 180 or more for a decent carb. 270 and the only thing you need to worry about are the wires and vacuum lines and your pcm will still be able to give you trouble codes if you ever have problems. someone else will have to chime in on details about what will be needed for the pcm and trans when swapping over to a carb. it may end up being more than you bargained for and as you stated rusty would be an understatement. until someone who has done the carb swap can chime in for now if i were you i would be leaning to fixing whats already there to make it easier.

 

[Don Jordan]

i wouldn't be concerned about the lower half and the upper plenum is only 70 bucks on rock auto and the whole spider kit is about 200 bucks. 250 for a decent carb intake and another 180 or more for a decent carb. 270 and the only thing you need to worry about are the wires and vacuum lines and your pcm will still be able to give you trouble codes if you ever have problems. someone else will have to chime in on details about what will be needed for the pcm and trans when swapping over to a carb. it may end up being more than you bargained for and as you stated rusty would be an understatement. until someone who has done the carb swap can chime in for now if i were you i would be leaning to fixing whats already there to make it easier.

You're probably right. As I stated earlier, I'm not big on mods. I'll talk to him; we have plenty of time. Thanks for your input!

 

[fastpat]

Why would anyone swap a carb into to use in a FI engine? It's my opinion that all of us should move further into the FI world, and leave the carb world behind where it belongs.

 

[Don Jordan]

Why would anyone swap a carb into to use in a FI engine? It's my opinion that all of us should move further into the FI world, and leave the carb world behind where it belongs.

I talked my him into not doing it, but to be fair, you can gain a good bit more horsepower by going to a carburetor. The FI on this vehicle is around 400CFM. Any aftermarket carb worth fooling with starts around 600CFM. Swithcing this FI system to a 750CFM carb will net you over 120HP increase - and that's not even changing cams. You can gain the same results by using a different FI system, but the cost is way up there. The problem here isn't the carb, it's getting the computer to control the transmission without the inputs. It just can't be done without spending a lot more money. Not to mention fine tuning a cabr takes a screwdriver and a wrench. FI takes a computer with the right software, which not everybody has that.

 

[fastpat]

I talked my him into not doing it, but to be fair, you can gain a good bit more horsepower by going to a carburetor. The FI on this vehicle is around 400CFM. Any aftermarket carb worth fooling with starts around 600CFM. Swithcing this FI system to a 750CFM carb will net you over 120HP increase - and that's not even changing cams. You can gain the same results by using a different FI system, but the cost is way up there. The problem here isn't the carb, it's getting the computer to control the transmission without the inputs. It just can't be done without spending a lot more money. Not to mention fine tuning a cabr takes a screwdriver and a wrench. FI takes a computer with the right software, which not everybody has that.

I understand quite well. The last carb engine I messed with was a '79 Mustang 5.0. It came with a 2 barrel carb, I pulled that manifold and carb and installed a Edelbrock manifold and Carter 650 four barrel. That, with the Comp Cams 268 cam was a stunning improvement. I did a few other tweaks, too.

My current engine is a TBI and it's pretty lame. I'm thinking about how to imrprove it, but a carb isn't in the picture. I'll see how much investment it will take to do the improvements versus an engine swap.

 

[retorq]

I talked my him into not doing it, but to be fair, you can gain a good bit more horsepower by going to a carburetor. The FI on this vehicle is around 400CFM. Any aftermarket carb worth fooling with starts around 600CFM. Swithcing this FI system to a 750CFM carb will net you over 120HP increase - and that's not even changing cams. You can gain the same results by using a different FI system, but the cost is way up there. The problem here isn't the carb, it's getting the computer to control the transmission without the inputs. It just can't be done without spending a lot more money. Not to mention fine tuning a cabr takes a screwdriver and a wrench. FI takes a computer with the right software, which not everybody has that.

Sorry but you aren't going to gain 120 HP with a carb and intake swap on that engine using the factory cam.

Those trannys didn't have a vacuum signal to assist with the kick down like the ones 20 years ago did. It was TPS driven so you will need a TPS signal to feed the ECU to get it to run the tranny correctly.

 

[fastpat]

Howell has 500 CFM throttle bodies for 5.7 engines.
https://howellefi.com/product/tbi-unit-500-cfm-gm-2-bbl-replacement-for-350-v-8/

See this article from 2009.
https://www.hotrod.com/articles/0906rc-throttle-body-injection/