Swap 454/4L80 from 92 C2500 into 88-98 C1500

[SKR]

So here's a question, inspired by this thread:

http://67-72chevytrucks.com/vboard/s...d.php?t=784239

I have a 92 C2500 with a 454 and a 4L80. I bought this truck to swap the transmission, and maybe the motor too, into my 81. Since I bought the 92 though I've been looking more into the swap, and it's more of a process than I thought. So for now the 81 is staying the way it is, and I have this 92 sitting in my driveway with no real use for it. And since I've had time to think and daydream I've started to wonder about building my own GMC 454SS.

I'm sure just like the 81, there's some work involved in transplanting this drivetrain into an 88-98 truck. The biggest question is, how much of the electrical stuff has to come over from the 92 to get the 88-98 to work the way it's supposed to? The thread I linked above makes it seem like more trouble than it's worth to swap over all the stock components. Is it possible to just use an aftermarket EFI and TCM to get it to run and shift, the same as I would have to in the 81? I assume I'd have to look to the aftermarket for a fuel pump and ignition as well. Is there anything in an 88-98 that needs the 92 electronics, or is there an aftermarket solution for everything?

I understand how backwards this looks, that my solution for a little work to swap a 4L80 is to buy another truck and with considerably more work swap the 4L80 and 454 into it. But these are things that happen when you have too much time to daydream, and it would be nice to have an OBS and a squarebody. I'm still at the daydreaming stage and probably the truck will just end up as a farm truck.



Isn't it ugly?

[AussieinNC]

Suggestion.....apart from the confusing header on your post...says 88-98 C1500....but your post lists "your 81"

Put a new crate 350 in your 81....then add the 4L80 with an aftermarket TCM....

Putting a 92 454, with its HUGE 255 HP !....and its fuel system needs would be a true nightmare...

Just my humble opinion...

and Oh yeah....that trailer is UGLY !

[SKR]

I didn't think it was that confusing, but maybe this will clear it up. I bought the 92 to take its 4L80 and put into my 81. Since then, I've had a new idea that involves buying an 88-98, and putting the 454 and 4L80 into that instead.

Is that going to be any more work than it would be to put it into the 81? Are there problems with putting it into an 88-98, that don't exist if I was to put it into my 81?

[Palf70Step]

Since you have the one truck, it will be not too bad. You'll need all the wiring,computer, & probably the dash to make the swap. It's not a simple swap out the motor like in the old ones, but I do like the idea.

[SKR]

Originally Posted by Palf70Step

You'll need all the wiring,computer, & probably the dash to make the swap.

Would I need any of that if I used something like a Holley Terminator to run the motor and transmission, and left all the stock 88-98 stuff in? I know the truck would run then, but what happens to the gauges, ABS, cruise, that stuff?

I know people swap LSs into these trucks, or convert from TBI to carbs. So there must be a way. I just don't know if they have to give anything up to make that swap work.

[Palf70Step]

That I do not know. Hopefully someone more wise than me will jump in.

[AussieinNC]

Why not just find a GMT400 that has a 454 already in it?

Way too hard to find all the specific parts needed to change a 350 variant over to 454...

Just my old mans opinion...

[SKR]

Originally Posted by AussieinNC

Why not just find a GMT400 that has a 454 already in it?

GMC didn't build a half ton two wheel drive shortbox GMT400 454. Chevy did, but I want a GMC. So that's one reason. And more importantly, buying a GMT400 with a 454 in it already doesn't solve the problem, which is to find a use for this 92. The motor and transmission are coming out of that truck, and whatever's left over is going in the garbage. That's already been decided. It can't stay in the driveway forever, and as long as it's there it's going to be plated and insured, and that can't go on forever either.

Originally Posted by AussieinNC

Way too hard to find all the specific parts needed to change a 350 variant over to 454...

Almost all the parts are right there in the 92, and it all works. It would take more parts to get the transmission into my 81.

[Tiger Joe]

the 89-92 swap would be easier. most of the connections are the same on 350 vs 454 tbi trucks so more than likely you could reuse the wiring harness. I think some of them share the same ECM, just different PROMs inside. the thread you linked to is talking vortec to tbi which creates a lot of problems.

if you wanted to swap it into the 81, its still doable, just would require removing the entire wiring harness and getting a standalone harness made

[AussieinNC]

Originally Posted by SKR

GMC didn't build a half ton two wheel drive shortbox GMT400 454. Chevy did, but I want a GMC. So that's one reason. And more importantly, buying a GMT400 with a 454 in it already doesn't solve the problem, which is to find a use for this 92. The motor and transmission are coming out of that truck, and whatever's left over is going in the garbage. That's already been decided. It can't stay in the driveway forever, and as long as it's there it's going to be plated and insured, and that can't go on forever either.



Almost all the parts are right there in the 92, and it all works. It would take more parts to get the transmission into my 81.

Lets light the fire here!

Sell the 454 from the 92, put the trans only into the 81, and go find a real truck, like a 454 SS CHEVROLET !!!!!!!!

[68 TT]

I did the same swap. 89 C1500 cab & 91 K1500 chassis with 94 K2500 donor TBI 454/4L80E/NP241. I ended up only needing to modify the main PCM wire harness through firewall grommet. The hole in the firewall where the wire harness passes through in the 89's cab was a different shape than the 94 donor vehicle.

It was either cut the section of metal out of the 94 and graft it into the 89 cab or remove the bulkhead shroud from the wire harness from the 89 and fit it to the 94 harness so it would fit. I chose to try the bulkhead shroud swap. It sucked but I got it done and it worked but was a very tight fit for all the extra wires in the newer harness. If I was to do it again I would opt for the cut and weld route instead.

You could avoid this entirely by getting a C1500 truck with the newer firewall design to start your build from. If you like the classic dash design I would go with a 94 as you also get a better grille design that won't fit on the older core supports and the A/C system is already 134a from the factory as well as having the max A/C feature the older ones don't.

I ended up pulling the 4L80E/NP241 and installing a T-400 due to other problems but it all cleared the C1500 / K1500 parts just fine.

Not really related but kind of. The 89 & 94 cruise control systems use mostly the same parts but some stuff is slightly different and the wiring is slightly different even through the common wire diagrams show it all as the same for 88-94. I didn't notice the differences until it was too late to properly document them. Swap the engine donor wire harness, steering column, pedal assembly and cruise control module and all connected wiring or the system may not function properly. I thought I had mine done correctly with a mix of parts that were in the best condition but it is not fully functional. It will engage and maintain speed but won't cancel when you step on the brakes. I need to spend some time at the wrecking yard with a complete 94 and do a forensic analysis of the components and wiring colors to see what I have in my assembly that is incompatible.