454 tbi with 4l85E swap into c1500 350tbi

[someotherguy]

All these years on this forum reading about these trucks and for some reason this never clicked with me... I may have to reconsider the engine swap in my red truck. Do the 3500HDs use the same black box PCMs as the standard GMT400s?

On the 7.4 there's no real difference under the hood of an 3500HD vs. the lighter trucks (other than the obvious we've already discussed.) The 8.1; I dunno - I haven't worked with one first hand to know anything concrete. My guess would be it's much closer to GMT400 stuff than GMT800 since everything else on the truck is still GMT400-era.

Here's an engine bay shot of a 2002 3500HD with the 8.1, note the little blue finned device near the coolant reservoir is aftermarket equipment; it's a bucket truck.

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On an off-hand guess you might need a slightly newer dash cluster - wasn't it '98 or '99 the, crap, man my memory is failing me on this...the fuel gauge went to PCM controlled? *Maybe* the dash harness is different, too? Crazy wild guess there so don't take it as gospel.

Richard

 

[someotherguy]

Sorry OP for going off-track on your 454 TBI swap! Any further discussion of an 8.1 swap ought to be a different post...

Richard

 

[df2x4]

On the 7.4 there's no real difference under the hood of an 3500HD vs. the lighter trucks (other than the obvious we've already discussed.) The 8.1; I dunno - I haven't worked with one first hand to know anything concrete. My guess would be it's much closer to GMT400 stuff than GMT800 since everything else on the truck is still GMT400-era.

Here's an engine bay shot of a 2002 3500HD with the 8.1, note the little blue finned device near the coolant reservoir is aftermarket equipment; it's a bucket truck.

You must be registered for see images attach

On an off-hand guess you might need a slightly newer dash cluster - wasn't it '98 or '99 the, crap, man my memory is failing me on this...the fuel gauge went to PCM controlled? *Maybe* the dash harness is different, too? Crazy wild guess there so don't take it as gospel.

Richard

That actually looks more like an 0411 PCM, it's definitely not a GMT400 style black box. Is this one of your old trucks or is there a chance that someone swapped the PCMs?

Sorry, I'll shut up about it after this.

 

[someotherguy]

That actually looks more like an 0411 PCM, it's definitely not a GMT400 style black box. Is this one of your old trucks or is there a chance that someone swapped the PCMs?

Sorry, I'll shut up about it after this.

Definitely an LS-style PCM as you would figure since the 8.1 is CNP style ignition, no distributor. Not my truck.. there's more than a few out there, seems like a full donor truck would be needed as there would be plenty of underhood items that would be different. It's all still in a GMT400 cab though so my feelings about the swap potential are pretty good overall.

Richard

 

[Busted Knuckle]

Its not too much work until you realize that half of what you thought is wrong.

 

[stutaeng]

FWIW, my little dream truck would be a RCSB C1500 with an 8.1/4L80E swap, and of course a 14 bolt out back, maybe leave it 6 lug and swap the front rotors to the C2500LD's so I don't have to go through that re-drill crap again on the rear axles like I did on my '94 C2500LD project years ago.

I'd leave the driveline stock otherwise, just for simplicity's sake, but I'd get a custom tune for the 8.1 to wake it up.

Yeah, you can build lots of power with an LS swap, but everyone is doing LS's, and you lose the "factory style" serviceability with all that custom harness mess. A 2001-2002 3500HD would be the perfect engine/pcm/harness donor candidate for this swap (and I'd source a 4L80E from a regular 2500/3500 to avoid the tailshaft issue), since it would be a GMT400-style harness and all other related parts, it just means I'd be limiting my project truck to a 96-up, the bummer about that being I prefer the 88-94's a lot.

Richard

So here's a question that been lingering on my mind for some time:

At what point is "beefing up" a 1500 make more sense to just start with a 2500/3500 go from there? 4L80e and a variation of the 14 bolt are already there with 3.73 or 4.10s. Frame and brakes are already beefed up too.

I always see guys ask these questions frequently... trying to modify/adapt a 2500/3500 part into a 1500. OP's question is a bit unique though.

I've mentioned before I have a GMT 800 '99 Silverado ECSB 4.3/3.42 that I want to do a 5.3 (or 6.0) and 4L80e and likely 4.10s. Not sure about swapping a 14 bolt....at that point might as well sell it and get a 2500, LOL.

I suppose on the GMT 400 line most of the 2500/3500 were long beds, and many folks don't get too excited about long bed project trucks?

Just a question that always lingers in me...

 

[someotherguy]

Its not too much work until you realize that half of what you thought is wrong.

Some of us have actually built trucks, from the ground up, so I wouldn't worry to much..

So here's a question that been lingering on my mind for some time:

At what point is "beefing up" a 1500 make more sense to just start with a 2500/3500 go from there? 4L80e and a variation of the 14 bolt are already there. Frame and brakes are already beefed up too.

I always see guys asks these questions frequently... trying to modify/adapt a 2500/3500 part into a 1500. OP's question is a bit unique though.

I've mentioned before I have a GMT 800 '99 Silverado ECSB 4.3/3.42 that I want to do a 5.3 (or 6.0) and 4L80e and likely 4.10s. Not sure about swapping a 14 bolt....at that point might as well sell it and get a 2500, LOL.

I suppose on the GMT 400 line most of the 2500/3500 were long beds, and many folks don't get too excited about long bed project trucks?

Just a question that always lingers in me...

I think the goal is to obtain something that wasn't available factory, or not easily available. OP sounds like he's building somewhat of a homemade 454SS with parts he has available due to the donor truck being rotted out. My project dream is something that never existed, a C1500 RCSB with the 8.1. Nice little hot rod made with a combination of factory parts.

Richard

 

[thegawd]

Theres an 8.1 parked at my neighbors that I can't stop thinking about. My wife was not to happy when I brought up what I thought about that truck. I could get it for very cheap, it runs moves and stops but the truck is rotted. 3500 full crew cab 8 foot box, ****** truck of all trucks. Im not sure what year but it looks like a gmt800 and I dont want that kinda can of worms.... just that 8.1 engine and whatever it needs to run. Wife is not on board! But I am the only one who knows about that truck and it is not being advertised for sale soooooo. One day.

Al

 

[stutaeng]

Theres an 8.1 parked 1 property over from where I live that I can't stop thinking about. My wife was not to happy when I brought up what I thought about that truck. I could get it for very cheap, it runs moves and stops but the truck is rotted. 3500 full crew cab 8 foot box, ****** truck of all trucks. Im not sure what year but it looks like and gmt800 and I dont want that kinda can of worms.... just that 8.1 engine and whatever it needs to run. Wife is not on board! But I am the only one who knows about that truck and it is not being advertised for sale soooooo. One day.

Al

You sure it's a GMT-400 C/K 3500? I don't believe they ever put 8.1 on them. They did, however, put them in the HD3500 GVWR 15,000 lbs, mostly in 2001 and 2002. I've seen a few like that around here. Prior to that it was 7.4s.

I saw a 3500HD Crew Cab a few months ago. It was a '93 model, and was beat to death. Looked like it was used by a roofer and had a big steel box on the back. Most of the ones I see here are regular cabs and were some sort of service or work truck. The service trucks actually seem very well taken care of mostly. Not so much for the work trucks.

Edit: Sorry, just saw you said it was GMT-800.

 

[someotherguy]

Yeah they used the 8.1 for several years in the GMT800's but those trucks would only serve as an engine (and possibly PCM) donor; you'd still need to figure everything else out or custom hack the harness. I do believe some of them came with the Allison transmission, too. Talk about your literal can of worms for a swap donor! The 2001-2002 3500HD IMO is a far better donor. (Or 2001-2006ish if you can get one from Mexico! shhhhhh...)

Richard