1997 5.7/4L60e carb conversion help needed

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Don Jordan

TYF Newbie
Joined
Jun 28, 2018
Posts
6
Reaction score
3
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

Full Access Member
Joined
Feb 15, 2016
Posts
2,473
Reaction score
1,713
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?
 
OP
OP
D

Don Jordan

TYF Newbie
Joined
Jun 28, 2018
Posts
6
Reaction score
3
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

Full Access Member
Joined
Feb 15, 2016
Posts
2,473
Reaction score
1,713
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.
 
OP
OP
D

Don Jordan

TYF Newbie
Joined
Jun 28, 2018
Posts
6
Reaction score
3
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

Full Access Member
Joined
Jun 2, 2018
Posts
163
Reaction score
70
Location
Upcountry South Carolina
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.
 
Last edited:
OP
OP
D

Don Jordan

TYF Newbie
Joined
Jun 28, 2018
Posts
6
Reaction score
3
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

Full Access Member
Joined
Jun 2, 2018
Posts
163
Reaction score
70
Location
Upcountry South Carolina
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

Full Access Member
Joined
Mar 4, 2010
Posts
3,018
Reaction score
10
Location
Kingman AZ
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.
 

Forum statistics

Threads
128,788
Posts
1,805,455
Members
91,768
Latest member
PascalBlues
Top