77 big10 roller 5.3 LS swap

[Gonzalo_3]

This is my first LS swap ever on a 77 big 10 Silverado. I found this truck in a field and its just a roller. I feel confident about the swap, however I just wanted to run some stuff by this forum to see if y'all have anything to say about my plan. I have a donor truck (2004 Yukon) and I plan on using the engine and engine wiring harness out of the donor. I will need a new body harness to wire everything back up. Another concern of mine would be mating a Th350 and making sure I have the correct engine mounts, transmission crossmember for a solid power train. My main concerns are with the mating of the LS and TH as well as the chassis wiring. Like I said this is my first swap and I'm looking for some help with my "pre swap thoughts". Thanks

 

[CountKrunk]

Does the donor truck not also have a trans?

 

[Edelbrock]

Ya, like he said - I would try to keep the LS engine with the "LS" trans, for several reasons.

 

[Gonzalo_3]

Ya, like he said - I would try to keep the LS engine with the "LS" trans, for several reasons.

Yes I have a 4L60 that works, however its slips and idk if I want to fight a uphill battle with this trans or swap it just to get another transmission. If i have to use it then oh well, but my thought was just to use a TH350.

 

[TotalyHucked]

Half the reason to do the swap is the modern, fuel injected engine. The other half is to gain an overdrive. Find another 4L60 or get that one rebuilt, would suck to go through all that work and still be singing on the interstate.

Seriously, it's no extra work to do the 4L60. Just 1 more leg on the harness with 1 more plug. Much harder to keep the old trans. I used Tejas Steelworks engine mounts, trans mount and fan shroud when I did mine. Very nice stuff. I'm tellin ya man, nothing better than to be able to comfortably run 80+ on the interstate and the truck is just loafing along. I can run out a quick list of stuff I used if that'll help ya. I've got 56k miles on it now and it's been awesome

 

[Gonzalo_3]

Half the reason to do the swap is the modern, fuel injected engine. The other half is to gain an overdrive. Find another 4L60 or get that one rebuilt, would suck to go through all that work and still be singing on the interstate.

Seriously, it's no extra work to do the 4L60. Just 1 more leg on the harness with 1 more plug. Much harder to keep the old trans. I used Tejas Steelworks engine mounts, trans mount and fan shroud when I did mine. Very nice stuff. I'm tellin ya man, nothing better than to be able to comfortably run 80+ on the interstate and the truck is just loafing along. I can run out a quick list of stuff I used if that'll help ya. I've got 56k miles on it now and it's been awesome

Thanks man and I would like that list plz

 

[Ricko1966]

Thanks man and I would like that list plz

Going to a 4l60/700r4 depending on what tires you are running and what current rear gear you have,you may end up having to change rear gears also. Do you know your rear gears and what tires you are going to run?

 

[CalSgt]

Prepare a plan for the fuel system which can be a costly addition to the EFI swap.

You’ll need a tank (or tanks) for an ‘87 with the fuel pump baffling. ‘87 fuel sending units, EFI rated pumps, fuel lines, add a return line, a tank switch rated for EFI pressure, fuel filter Etc.

You could do a fuel cell instead but that comes with its own list of costs…

There may be other options for the fuel system too but I don’t know what they are

The truck side part of the swap harness is simple and nearly the same as what’s already there, here are some basics.

Purple wire to starter
Brown (IIRC) alternator exciter wire
Two red wires from battery (positive lug on starter and back of alternator each with fusible links)
Green (IIRC) A/C pump
Green temp sender
Tan oil pressure sender
Pink ignition coil (if not part of the PCM harness)

For the PCM you’ll need to feed it:
One constant hot wire (batt)
One wire Hot During run and crank but open when the key is off.
(Most of the positive circuits in the truck will cut off during engine start which will not work)
Ground
Everything else should be on your donor harness