8.1 Swap

[Wicked Wolf Auto]

I'm having a hard time getting the 350 in my 73 running. There's absolutely nothing wrong with it other than it's stock. I've been contemplating an 8.1 LS swap and would love to hear some real world thoughts on the swap. Why an 8.1? why not. Price in the salvage yards is the same between an 8.1, 6.0 and the 5.3 so why not go big?

 

[dyeager535]

I'm having a hard time getting the 350 in my 73 running. There's absolutely nothing wrong with it other than it's stock. I've been contemplating an 8.1 LS swap and would love to hear some real world thoughts on the swap. Why an 8.1? why not. Price in the salvage yards is the same between an 8.1, 6.0 and the 5.3 so why not go big?

Obvious question, why are you having a hard time getting the 350 running? Motivation may shift once it runs!

 

[sweetk30]

https://ck5.com/forums/threads/l18-8-1l-swap-resource-thread.308019/

 

[ZooMad75]

Not saying this to sound like a jerk, but if you are having problems getting a 350 with a carb running, putting an 8.1 in might be a bit more of a challenge.
As far as practical experience an 8.1 in a square is fun. Torque down low, lugs like a tractor in low range and pulls like a freight train.

The link above by @Larry contains everything you need for details to complete the swap. It's required reading if you are serious about using one.

 

[Kay86K5]

Technically speaking, the 8.1 is not an "LS" motor, though the injection on it is virtually identical to all other LS motors.

Bolting an 8.1 into a square is easy peasy. ORD big block engine crossmember, and motor mounts that are in the square already will work just fine. Most all GM bellhousing bolt up to 8.1 (though if your running a half ton 700r4 or TH350 it most likely won't last long unless you do a rebuild with some upgrades). Then fueling you will need to pretty much redo most of it since yours is a '73. Probably best way to do it is get a TBI tank from a square burban, put an EP381 pump in it, and then run lines that handle the higher pressure up to the motor. Electrical, just purchase a full stand alone harness/computer and call it good. Exhaust, can just leave the stock manifolds for 8.1 on there, just need to clearance the frame, or get manifolds/headers off any older 7.4 and they will bolt up to the 8.1 and clear the frame on a square.

With 6.0's and 5.3's you have to do pretty much all that plus worry about conversion motor mounts, and exhaust is a bit more tricky. If debating 6.0 vs 8.1, I honestly say 8.1 would be better. More low end tq and more horsepower in stock form, and the 6.0 won't get much better mpg's then the 8.1, so would rather have the power (unless you plan to build the motor, then go 6.0 as the aftermarket support is much greater for cheaper). If care more about drivability on street and economy, then go with the 5.3

 

[Wicked Wolf Auto]

Guys, it's not that I can't get it running. Its that I don't think I'll be happy with the stocker when I get it done and will end up yanking it out anyway.

 

[ZooMad75]

Guys, it's not that I can't get it running. Its that I don't think I'll be happy with the stocker when I get it done and will end up yanking it out anyway.

You won't be happy with a carbd 350. After most cars /trucks having fi for the last 30 years going back to a carb with all the issues they come with its hard to justify putting up with it. Hard to start cold or hot, don't like acholol enhanced fuels and require adjusting to keep them tip top.

We are so spoiled by being able to hit the key and go. That's why any upgrade to fi is great, but add 8.1l of displacement and you get a really fun truck to drive.

 

[Wicked Wolf Auto]

Well I just went through the bulk of Larry's thread. Awesome information! I'm sold! Gonna start sourcing an 8.1

 

[skunked]

I really like the 8.1, that with a 4L80E is the next drivetrain setup for my truck.

 

[Larry]

Technically speaking, the 8.1 is not an "LS" motor, though the injection on it is virtually identical to all other LS motors.

Bolting an 8.1 into a square is easy peasy. ORD big block engine crossmember, and motor mounts that are in the square already will work just fine. Most all GM bellhousing bolt up to 8.1 (though if your running a half ton 700r4 or TH350 it most likely won't last long unless you do a rebuild with some upgrades). Then fueling you will need to pretty much redo most of it since yours is a '73. Probably best way to do it is get a TBI tank from a square burban, put an EP381 pump in it, and then run lines that handle the higher pressure up to the motor. Electrical, just purchase a full stand alone harness/computer and call it good. Exhaust, can just leave the stock manifolds for 8.1 on there, just need to clearance the frame, or get manifolds/headers off any older 7.4 and they will bolt up to the 8.1 and clear the frame on a square.

With 6.0's and 5.3's you have to do pretty much all that plus worry about conversion motor mounts, and exhaust is a bit more tricky. If debating 6.0 vs 8.1, I honestly say 8.1 would be better. More low end tq and more horsepower in stock form, and the 6.0 won't get much better mpg's then the 8.1, so would rather have the power (unless you plan to build the motor, then go 6.0 as the aftermarket support is much greater for cheaper). If care more about drivability on street and economy, then go with the 5.3

What he said! Looks like at least one person has paid attention to all my preaching over the past 10 years

If you were building a go-fast hotrod, I’d say go with an LS engine all day long but for a heavy 4x4 you can’t beat the out of the box low RPM/high torque of the 8.1. It is a great alternative to a diesel. Personally, I do not care for the modern high revving engines like LS engines that must be spun up so high the pistons are practically swapping holes to muster power any out of them. Not something that fits the 4x4 world well outside of maybe mud racing. Very poor match for trail riding

I tell ya, after doing two 8.1 swaps and one 5.3 swap the 8.1 is a much easier install. It is pretty much a direct bolt in. No BS with engine mounts or exhaust manifolds to deal with. The 8.1 drops right in exactly the same as any other old SBC or BBC. It will even except older BBC manifolds so sourcing manifolds that fit an old square body is not an issue where cutting the frame or sourcing hard to find manifolds can be an issue on LS engine. The 8.1 also leaves you enough room between the back of the engine and firewall to actually stick your hand back there whereas the LS is so tight to the firewall a 3 year old can barely get their hand in there. The 8.1 cost no more than an LS engine and often even less when an 8.1 is replacing an older BBC plus most people know nothing about 8.1s and don't charge the L$ premium for them. The only thing difficult about an 8.1 is finding one and finding the correct accessory brackets if you intend to run A/C. My thread has tons of info in it to help you along and there is a large 8.1 group on Facebook that can help with guidance.

Good luck with the search. For the search, try finding an 2001/2003 Chevrolet Express or GMC Savanna or 2001/2002 GM 3500-HD truck (old body GMT400 chassis cab with the I-beam front axle) as they will have the correct accessory brackets already on them.

 

[Wicked Wolf Auto]

Already found one in a 2001. It's at a "u pull it" . one of the parts pullers quoted me $25/hr to yank it out. Well worth it IMHO. Should be into it for less than $500 . He's going to get it out Friday or Saturday then the cleanup and parts buying can start. I think I'll stick with my SM465 for now, maybe swap to a 6 speed down the line. I also have dual tanks but after reading your post I think I'll just go with 1 new efi tank for now. This truck won't be going on any long journeys.

 

[skunked]

That's a steal.

 

[Kay86K5]

Good luck with the search. For the search, try finding an 2001/2003 Chevrolet Express or GMC Savanna or 2001/2002 GM 3500-HD truck (old body GMT400 chassis cab with the I-beam front axle) as they will have the correct accessory brackets already on them.

Plus with those years you get the return style fuel rail with the adjustable regulator...makes running fuel lines easier and also allows some adjustability...so always a plus

Already found one in a 2001. It's at a "u pull it" . one of the parts pullers quoted me $25/hr to yank it out. Well worth it IMHO. Should be into it for less than $500 . He's going to get it out Friday or Saturday then the cleanup and parts buying can start. I think I'll stick with my SM465 for now, maybe swap to a 6 speed down the line. I also have dual tanks but after reading your post I think I'll just go with 1 new efi tank for now. This truck won't be going on any long journeys.

Didn't know you had an SM465...just rock that for a while. You will need to get an 8.1 specific flywheel, but your existing clutch pack/disc should bolt up to it just fine (might have to widen the bolt holes on the pack just a smidge to accept the 8.1 bolts, but not a big deal at all), and your off to the races.

 

[Larry]

Didn't know you had an SM465...just rock that for a while. You will need to get an 8.1 specific flywheel, but your existing clutch pack/disc should bolt up to it just fine (might have to widen the bolt holes on the pack just a smidge to accept the 8.1 bolts, but not a big deal at all), and your off to the races.

Exactly! I ran a 465 behind my 8.1 in the K10 for the first couple years. I even used the same clutch and pressure plate from the 454 it replaced. If I didn’t do so many long-distance trips where Overdrive is a must I’d still rock the 465 today. Such a much stronger trans with better granny gear over a NV4500 (mine is the later 4500 with the sucktastic granny gear).

 

[Wicked Wolf Auto]

Larry, maybe I missed it in your thread, not alot is discussed about exhaust other than headers. I will need to pass IM, I don't think it will be an issue but I'm curious, will I need cats and/or o2 sensors for the 8.1 to run properly or just have all that junk deleted when the tune is written?

 

[Kay86K5]

Larry, maybe I missed it in your thread, not alot is discussed about exhaust other than headers. I will need to pass IM, I don't think it will be an issue but I'm curious, will I need cats and/or o2 sensors for the 8.1 to run properly or just have all that junk deleted when the tune is written?

You will need at least 2 O2's to run the motor property, and will add those closer to both headers/manifolds. Usually for emissions you need to install cat's, which is easy, whenever you do exhaust just make sure to add some. The other thing is if you get that 2001 motor, it is equipped with EGR (that tube off the back of the motor). In 2004 (if I remember correctly), GM deleted it from the factory and just have a block off plate on the intake and manifold. So depending on how closely your emissions test will look at that, you may have to keep it (would be real nice if you could just delete it and use the block off plates and then also delete it in the tune). I can't think of anything else emissions wise on the 8.1...Larry can correct me if I'm missing something

 

[Wicked Wolf Auto]

egr delete is easy and my emissions guy won't know the difference lol. Cats are easy enough and I'll just buy headers with o2 bungs. Is 3" exhaust from the headers back too much for these motors?

 

[Kay86K5]

egr delete is easy and my emissions guy won't know the difference lol. Cats are easy enough and I'll just buy headers with o2 bungs. Is 3" exhaust from the headers back too much for these motors?

No, 3" is fine, that's basically what I run on my crew cab. It was kinda hard to fit 3" tube around the t-case and cross-member, but mine is more of a tow rig so didn't have to worry too much about ground clearance. I have 3" off the headers that conjoin to a Y pipe just past the t-case. Y pipe is 3" inlet and 3.5" single outlet. Then a single 3.5" all the way out the back to a 4.5" tip (with a flowmaster in the middle of that. Looks real good, and I think it sounds good too, but I like a bit of a louder muffler, cause I'm a young buck as @mrk5 likes to call me . I can always change the muffler out easily later on if I want to

 

[Wicked Wolf Auto]

Kay86K5 What headers are you running?

 

[Kay86K5]

mid-length headman headers