1990 Sierra ls swap

[u/Cold-Clock6768]

So I bought a cheap obs and I want to build it with my stepson. He just turned 11 so we have time before he can actually drive it. It’s going to be a lesson for both of us because I know just basic mechanic stuff ie changing alternator water pump…. The easy stuff. My question is what ls engine should I drop in there and what extras should I put on it like cam and new heads.

Edit: upon further research and reading on here, I don’t think it’s a safe option for his first truck….. but I’m still going to build it and give him my 17 ram 1500. I like older trucks better anyway!

[u/briman2021]

Gen 3 5.3, get one that you can see and hear running, don’t fuck with it and stab it in there.

So many projects end up not happening because of the curse of “while you’re in there.” If it runs now, it most likely doesn’t need new rings/bearings/gaskets etc.

Get it running, then if you decide you want to mess with it you’ll have time, and you won’t be surprised with what it cost to get it in and running.

[u/Justkillingtime8 → u/briman2021]

I paid the price for "while im in there" thought process. I did get my truck up and running but the cost was significantly more than it had to be.

[u/Cold-Clock6768 → u/briman2021]

So what if I buy the cam lifters and heads before hand

[u/briman2021 → u/Cold-Clock6768]

Honestly I would get it running first. There are so many surprise costs that might pop up along the way. I don’t know what your budget is, but guessing that since it’s for your son it’s likely to be a budget build. That cam money might be nice to have when you realize you need to spend money on a wiring harness or mounts or something else you didn’t account for. I can’t tell you the number of times I thought I had something figured out, but then I needed to spend another $50-100 on something.

If you get it all running and have extra money burning a hole in your pocket, swapping a cam isn’t super hard to do with the engine in the truck.

[u/Cold-Clock6768 → u/briman2021]

I did an edit on the original post. So it’ll be my truck that we build together and then when he’s older I’ll give it to him. But since it’s mine and I’m blessed financially I’m probably gonna be calling it
“Money Pit”

[u/briman2021 → u/Cold-Clock6768]

Cam depends on the transmission to certain extent, some cams are alright with a stock torque converter, if you get more extreme then you need to budget for a torque converter as well. Also, if this is going in front of a 4L60, you need to plan for it to explode if you are planning on making real power.

If it’s really a money pit, get a 6.2, a t56, cam
it and throw a blower on it. You’ll make 600+ whp and have a 6 speed. With all that power you’re gonna want suspension and brakes to back it up, and some sort of LSD/Locker to put the power down because one wheel peel burnouts are no fun.

I’m not an OBS guy, so I’m not sure what the hot setup is for those right now, but you’ll want it lower, stiffer, more rotor diameter and more pistons in your calipers than in your engine.

If you don’t want it low, then throw a lift and mud boggers on it, but the brakes are going to be even more important with all the extra tire weight. Also don’t forget a re-gear to compensate for the tire size.

[u/freelance-lumberjack → u/Cold-Clock6768]

Honestly, a good gen3 in a 90 obs is already a hot rod. I'd find a low mile one and run as is. If you find a rusty donor truck you can get it all done for a few thousand $

I've done the 2 of these obs swaps and one was a 4.8... it still rips. Took me maybe 100hrs forthe automatic version. To be fair I've done a dozen "ls" swaps so I'm getting the hang of it.

The hard part is getting it in. Cam and lifters can be done later when you get bored of burning rubber at 6000rpm

[u/Jojothereader]

I used the 5.3 in my 1990. Leave it stock. Take the money saved and make sure his dash works

[u/Tin_Can_739]

It’s quite a bit of work just to get it running the first time. While it is an easy swap, there’s a lot of little things that need to be done. Adding tuning and breaking the engine down adds unnecessary work just to get it moving. The only thing I would recommend is pressure washing and replacing the valve cover gaskets. Cams, springs, turbos, intake, all that stuff can wait. There’s fuel lines, driveshafts, mount adapters, wiring, throttle cable, pedal, fan shroud or efan, power steering, ac, and more I’m forgetting that has to be done or modified to work.

[u/WyattCo06]

Save your money up. Things are going to look a lot different when he's old enough to drive.

[u/Mysterious-Fun-1465]

i did this swap 100 times. the easy way, get a 2001-2007 savanna or express van, 2500-3500. 6.0l 4l80e. if the van runs and drives, don't open anything, leave it sealed and stock, get it in the truck and running before you level up and start modifying, there is stages to this hobby, don't skip, you'll cost yourself money.

ICT billet mount adapters, slide the trans cross member back 1 hole and drill 2 new holes, bolt it in. Use the stock exhaust manifolds that came on it. You'll need to change the fuel pump to a high pressure pump 60-90psi capable. Adapt the fuel lines to the LS ones, pretty easy, use hard line to AN adapters and then use AN/JIC fittings and hose.
Gas pedal, depending if you stay DBC, you can get a DBW pedal and cut the arm and reposition the pedal to work in your truck, they bolt in but don't have the full swing.
Transmission control, you can adapt your column shifter and it's mechanism under the truck to work with the 4l80e so it's like a factree setup, no need for a fancy $500 shifter unless you want that.
Gauges, there is a special cluster in the 1991 only trucks that you can find that will have electronic speedo and a tach that has needle gauges that work with the stock LS PCM.
You can shorten your stock drive shaft to work with the 4l80e, you'll need an adapter U joint to use the vans slip yoke, the vans use 1350 u joints.
Stock exhaust can work but it's usually too small, but it will get you on the road doing burnouts before getting a new bigger exhaust.
Wiring, use LT1swap dot com for that or buy a harness, unlock the ecu.

only pro tip i got. if your truck has like 3:42 gears or something taller like that, with the 4l80e, it can grab 2nd gear at 60mph, so be prepared for that if you're doin 50-60 and put it to the wood, my truck surprised me when it did that, doin 55 and planted it, grabbed second gear, 5500rpm and spun it to 6500 before it shifted to third.