Squarebody Chevy 8.1 Swap

Introduction

The 8.1. What is it exactly? In a nut shell, when GM switched from 305 and 350 small blocks to the new "LS" style 4.8s, 5.3s, 6.0s, etc, they also developed an engine to replace the 454. The 8.1 is that engine.

It was introduced in the same basic time frame as the "LS" Engines. First offered in the 2001 gmt800 trucks, they were available in the 2500/3500 series trucks and in 2500 Suburbans. They ran from 2001 to 2006 in those platforms before it was discontinued and GM stuck with just the "LS" engines and the Duramax.

The 8.1s were also used extensively in many medium duty applications such as box trucks, motor homes, marine, generators, and lots of other miscellaneous applications.

At some point, after GM discontinued production, a company called PSI purchased the rights to the engine and continues to produce them to this day. PSI even has an 8.8 variant. These engines are often installed in busses and various medium duty applications.

Medium duty Truck configuration.

'01-'06 GM 3/4-ton / 1-ton truck configuration.

Marine application.

That's it for a brief run down of where they come from. For the purposes of this article, most of the time I'll be referring to '01-'06 Chevy/GMC 2500/3500 engines. These have the "L18" engine code. Engines from these trucks could be considered somewhat "rare", at least in comparison to the number of "LS" engines and Duramax engines. However, they really aren't all that rare and can be found in many junk yards across the country and/or on ebay.

With regards to transmissions, it's important to note that pickups came with Allison transmissions, and suburbans came with 4l80e transmissions behind their 8.1s.

What makes them special? The 8.1 is commonly referred to as a hybrid of an "LS" engine and a traditional Big Block Chevy (BBC) engine. And that's a pretty accurate way of describing them. The 8.1, which is 496 cubic inches, Shares most of its architecture with the BBC, but sports a plethora of design elements of the "LS" engines. Easily the biggest difference from the traditional BBC is the cylinder heads. All 8.1's use iron heads. Aluminum heads are available aftermarket only. They bare a striking resemblance to the "LS" cylinder heads with respect to the intake ports. It's clear that GM applied that R&D to the 8.1 heads. Speaking in terms of it being a hybrid of the two engine designs, the exhaust ports are virtually identical to a BBC. Any exhaust manifold or header that would bolt up to a BBC, Will bolt to the 8.1 head with no modifications. So you have "LS" style intake ports, and BBC exhaust ports.

8.1 cylinder head intake ports.

Traditional BBC Intake ports.

"LS" Intake ports.

Back to the intake. There are very few aftermarket intake manifolds available for the 8.1 due to the unique design of the heads. Notably, DART makes an intake manifold for the 8.1 which allows for the use of a carb, and traditional BBC distributer driven by the cam just like a typical BBC. However the DART intake is fairly spendy, and is chronically out of stock... Their is a company called RAYLAR engineering that has recently (2022) developed an aftermarket EFI intake, designed to be an upgrade of the original intake. But they are even more expensive than the DART intakes... There is a popular intake mod for the original intakes that helps them breath better. This "8.1 intake mod" does require cutting and welding on the intake. The 8.1s mostly all came with electronic (aka drive by wire) but can be swapped to drive by cable throttle body following the same basic procedure as the "LS" engines.

Factory 8.1 intake manifold.

Raylar intake manifold.

Dart Carbureted 8.1 intake manifold.

In sharing with it's "LS" counter parts, the engine management, electronics, wiring, etc is extremely similar between the 8.1 and "LS". In fact, they use the same ECM, just with different calibrations. The wiring uses mostly the same connectors and wire color logic. An "LS" holley termintator will work on the 8.1 for example if you wanted to. Or, anyone that can modify and tune the harness and computer for an "LS" can do the same process on an 8.1.

Why don't more people use them? What are the downsides? There are two main reasons why they aren't more common for swaps. Number one, they are less common than virtually every other engine that was available in the 2001-2006 trucks so they aren't as easy to get your hands on as the other more common engines. Number two, is the lack of aftermarket support. The aftermarket for the "LS" engines is practically unlimited. Whereas the 8.1s really only have a couple of companies making aftermarket parts for them. Raylar Engineering being the biggest for consumers and PSI being the biggest for industrial/commercial purposes. There are only a handful of aftermarket camshafts for them. They also had a bad rap for not being able to handle more than 550hp due to pistons cracking, although this seems to be more of an old wives tale than actual fact. The last factor in them being less commonly used for swaps vs the "LS" is the weight/size of the engine. Most LS engines have aluminum heads and plastic intake. The iron heads and aluminum intake on the 8.1 adds a considerable amount of weight. In the neighborhood of 150lbs. And of course the physical size of the 8.1 is considerably larger than the "LS" engines. Other than those factors, the 8.1 has proven to be an incredibly reliable engine. Every bit as reliable, if not more reliable, than the "LS". These are generally considered "500k mile engines".

What about performance? The 2001-2006 Chevy/GMC truck versions of these engines are factory rated around 340hp and 455ft.lb. They even boast 400ft.lb at only 1000 RPM! Making them an excellent choice for heavy vehicles/ people who tow. A performance tune on the computer and a set of headers can put these engines at around 400hp and 550ft.lb. Worth mentioning with regards to performance is a couple of YouTube video series that have been done on the 8.1. First up is the Richard Holdner YouTube channel. He does a lot of engine testing on all kinds of engines. But has done some good testing on the 8.1. His videos are well worth checking out. He's also put a turbo on the 8.1 and produced 664hp and 878ft.lb at only 7.8 PSI of boost on an otherwise stock engine. Then there is the Lawrence LT Toleman YouTube channel. He has a stock, junkyard 8.1 swapped into is early 2000's Silverado 1500. The engine is 100% stock but has a big turbo on it running around 17 PSI of boost. He put down 817hp and 1140ft.lb AT THE WHEELS! On a stock engine! Incredible. These are REALLY good engines.

Richard holdner 8.1 dyno. Stock hp/tq.

Richard Holdner 8.1 dyno. Turbo hp/tq.

LT Turbo 8.1 HP.

LT Turbo 8.1 TQ.

Installation

We're going to focus on installation into the 73-87(91) square body trucks for this article.

Being that this engine shares so much with the traditional BBC engines, installation is pretty straight forward into these trucks. The bellhousing pattern is the same as any SBC/BBC, although the bellhousing bolts are metric.

You can see here the traditional chevy bellhousing.

Closer view of bellhousing, Allison flex plate, and crank sensor.

The 8.1 flex plate bolts right up to the earlier style transmissions like a th400. The 8.1's also accept flex plates from any internally balanced SBC engine. I had to use a mid 70s Chevy truck 350 flex plate on my 8.1 swap because I'm still running a th350 and it's torque converter has a smaller bolt circle than the th400s.

For motor mounts, the engine is drilled for both the early style 3 bolt clam shells that came on SBC/BBC engines, and they are drilled for the later 4 bolt "LS" style mounts. For my swap, I used the clam shells that were on the 350 that was in the truck before the swap. Only two modifications were needed to accomplish this. On the driver side, there is one drilled boss on the engine block which is used for the 4 bolt mounts that interferes with the old style clam shells. The one offending boss just needs ground down about 1/8" to allow the clam shell to sit flat. The only other thing that is needed is metric bolts. Once you have the clam shells bolted to the engine, install is just like any other SBC/BBC. No adapter plates or flexplate spacers are required. I did run into an issue on my swap where I had to use the upper frame mount holes on the passenger side motor mount and the lower set of frame mount holes on the driver side motor mount to get the main motor mount bolts to line up. I think this was because I used the 350 clam shells which are slightly different than big block clam shells.

Driver side engine mount.

Passenger engine mount.

Engine set in place. Passenger engine mount.

Engine crossmember clearance. The 8.1 uses a large, cast aluminum oil pan. If swapping an 8.1 into a 2wd square body, no modifications are required to the oil pan or crossmember. Plenty of clearance everywhere. If swapping into a 4x4 square body, there are clearance issues between the oil pan and engine crossmember. It is possible to space the engine up enough to clear, but it's still pretty close. The most popular thing to do in this case is to swap to an off-road design BBC engine crossmember. This allows for plenty of clearance around everything. However, Off-road design states that at least a 2.5" Lift is required to clear their engine cross member at the front axle. Alternatively, you can cut/notch your factory 4x4 engine crossmember for oil pan clearance and not have to run a lift kit. Again, for me, since I was doing my swap into a 2wd, no modifications were required. If I was swapping an 8.1 into a stock height 4x4, I would cut/notch my crossmember and/or space the engine up. If I was 8.1 swapping a lifted 4x4, i would use the off-road design BBC engine crossmember.

Last note for installation is in regards to the A/C pump. The 8.1s mount the A/C compressor in the same spot as the "LS" engines. Down low on the passenger side. This location interferes with the passenger frame rail in that area and wont work. You can notch the frame to clear the A/C pump, but it takes a lot of cutting in an area that really could use all the strength it can get so I don't recommend it. There are a couple options if you want to retain air conditioning in your truck. One, is to use one of the other styles of 8.1(most popular is the medium duty truck applications like Kodiak trucks) front accessory brackets that mount the A/C pump up high, although they are generally spendy and harder to find, or there is a couple smaller companies that make aftermarket A/C brackets but they aren't very well marketed. Thankfully, in my case, the truck doesn't have A/C so I didn't have to worry about all that. If I were wanting to do a swap with A/C, I would use the Amos Garcia A/C bracket listed in the resources section.

Larry's 8.1 using the Off-Road design BBC engine crossmember.

A closer pic of Larry's 8.1 showing clearance between the oil pan and the ORD BBC engine crossmember.

The Amos Garcia A/C compressor bracket.

Electrical

As stated above, the engine management system (ECM, Wring harness, Fuel injection stuff) is all nearly identical to the "LS" engines. If you're a DIYer, any of the guides for modifying an "LS" engine harness will pretty much apply to the 8.1 harness. If you aren't familiar with lt1swap.com, all the info you need is there for modifying the harness. For the ECM, you can either program it yourself using something like HPTuners, or have it tuned by any company that does "LS" computer tuning. You do have to have the ECM programmed to at least disable the Vehicle Anti Theft System (VATS). Without this being done, the ECM will only let the engine run for a few seconds before it shuts the engine down. If you aren't as much of a DIYer or just want an all new wiring harness, the most popular place to go for the 8.1s is Howell. They're spendy, but good quality. I'm familiar with modifying the "LS" harnesses and have done several of them so I chose to modify my harness myself. On mine, because the engine originally came in a pickup, it had Allison transmission controls and wiring. I wanted 4l80e transmission control/wiring, so I removed the Allison specific wiring and added in the 4l80e stuff which essentially converted it to a suburban style harness. At the time of this writing, I'm still running a th350 but plan to swap to a 4l80e when this transmission goes out. As Such, I simply have the ECM tuned to believe it has a manual transmission.

Bottom line, while you cant directly use a "LS" engine harness on these engines(due mostly to different routing of the harness around the engine), it is so similar that almost everything which applies to the "LS" engines, also applies to the 8.1s as far as engine electrical is concerned.

Reworking the 8.1 harness

Wrapping up.

Harness rework complete.

Front Accessories

The front accessories on an 8.1 that came out of an '01-'06 Chevy/GMC trucks have a very similar configuration to the "LS" engine's setups. The positioning of the alternator, power steering pump, water pump, and A/C pump are the same between "LS" and 8.1s. As stated above, and as with the "LS" engines, the A/C pump will not work in the stock, low passenger position. Everything else has no clearance issues. Also note that even though the alternator and power steering pump are in the same position as the "LS" engines, the bracket is different.

Power steering pumps. I believe that all 8.1 trucks used hydro-boost brakes which uses the power steering pump to provide brake assist as opposed to vacuum assist. These pumps are identical to a power steering pump designed for use with vacuum assist brakes except that they have an additional return line port on the pump housing. If you have a hydro-boost pump, and are using vacuum brakes, you just need to cap the extra return line. "LS" style power steering pumps will bolt onto the 8.1 brackets also. My engine was missing it's power steering pump so I used one from a 5.3 vacuum brake truck.

For power steering lines, you use the factory power steering hoses for the truck you're swapping into. All you have to do is remove the fitting at the back of the 8.1 pump, and replace it with the fitting from the back of the pump of the truck you are swapping the 8.1 into. The square body fitting screws right into the 8.1 power steering pump, and then your pressure line threads right into that. The return line just slides onto the return line nipple on the pump and gets clamped in place. So the power steering pump is easy. It's worth noting that if your 8.1 came from a medium duty application, it might have "ZF" power steering pump or a hydraulic pump. If so, you'll want to swap it for a standard pump.

The alternator is the same as any "LS" truck engine. The ECM controls the alternator voltage/current output. So the alternator is easy.

The water pump inlet is close to the same orientation as a traditional BBC, But points more horizontally as opposed to the 45 degree downward angle of the BBC. What i did was used a combination of a 5.3 truck lower rad hose, and a factory BBC hose cut and trimmed to fit with a splice in the middle with a nice barbed aluminum coupler. But there are other options. One is to just use a universal flex hose and many folks have done that with good success. Alternatively, you can swap to a different style of front end accessories such as Kodiak/Express Van setups which allow for use of a standard square body BBC lower radiator hose. Check out Dirty Larry's thread(listed in the resources section) for a ton more info on that, and the various A/C setups. These water pumps take a thread on style fan if you are using a mechanical cooling fan like me. They will accept many different types of fans. Mine is running a 6.0 "LS" cooling fan that I had laying around.

Bottom line, if you don't need A/C, all the factory '01-'06 truck's front end accessory drive stuff will work.

Power Steering lines

Front accessories

Fitting removed from rear of the power steering pump.

Exhaust

As stated above, Any Traditional BBC exhaust will bolt up to the 8.1 heads. The stock 8.1 exhaust manifolds will not work without significantly notching the frame which I do not recommend. Especially with as many options are available without having to modify the frame. On my swap, I elected to use stock square body BBC exhaust manifolds. They bolted right up with two exceptions. Of course, as with all fasteners on the 8.1, the exhaust manifold bolts are metric. From the factory, the 8.1 comes with studs for the exhaust manifolds instead of bolts. The factory studs will not work with a swap in a square body as they are in the way of the manifold/header being put in place so the studs need removed and bolts need to be used instead. In addition to that, the driver side exhaust manifold required some grinding on the block for clearance. The driver side knock sensor also has to be re-located. The passenger side bolts up with no clearance issues but just test fit them before you put the engine in the truck if you are using stock square body manifolds.

Any header that is meant for a square body with a BBC will work on an 8.1 with no issues. You obviously also will need to add provisions for the o2 sensors.

Driver side.

Passenger side.

Cooling

Not a lot of special consideration is required as far as cooling is concerned. I used the stock square body 350 radiator and the aforementioned 6.0 Cooling fan. The stock fan shroud also works perfectly. As stated above, for the lower hose I used a combination of a 5.3 truck lower hose and a BBC lower radiator hoses spliced together with a coupler in order to get the fit and form I was after. The lower hose for a 5.3 truck would have worked but the diameter on the water pump was too big for the hose. A universal flex hose is what many people use for the lower hose. For the upper radiator hose, I used a universal hose that had a 45 degree molded in and had the correct diameter for the radiator and the thermostat housing. Although from what I gather, the stock upper rad hose from an 8.1 truck will also work. For the heater hoses, there is one port on the engine, and then you'll use the port on the radiator for the heater core return. Standard 5/8 and 3/4 heater hose is all that is needed for that.

Stock Square Body Radiator and shroud with stock "LS" mechanical cooling fan.

Lower Radiator Hose

Upper Radiator Hose

A guy on Facebook sent me this. It looks like it is a perfect fit lower radiator hose. I have not used it personally but it looks promising. It is Master pro part number 21178.

Fuel System

Starting in '87, most square body trucks were equipped with Throttle Body Fuel Injection(TBI). The fuel tanks in these TBI equipped trucks included an important baffle in them which helps keep fuel from flowing away from the in tank fuel pump. Pickups, blazers, and suburbans are included. The fuel tanks are all backwards compatible in all model years.

The most common approach with these trucks when doing an "LS" swap, or 8.1 swap, is to use the fuel tank(s) from a TBI fuel injected square body that matches your model. So if you have a '73-'86 pickup, use '87 pickup fuel tank(s) and sending unit, if you have a '73-'86 blazer, use an '87-'91 blazer fuel tank and sending unit, if you have a '73-'86 suburban, 87-91 fuel tank and sending unit. For the fuel pump, for stock engines, the most common pump to use is the AC Delco EP381 fuel pump. It drops right into the TBI fuel pump hanger/sending unit but provides the proper pressure needed for the "LS"/ 8.1 fuel injection system.

From there you have several options for fuel lines. Best would be to use AN Braided lines from the fuel sending unit, to new hard lines on the frame, and then AN braided from the hard lines on the frame to the fuel rail. One of the other options are what I chose. I used Gates High pressure fuel injection rubber line from the fuel sending unit, all the way to the fuel rail. I also added protection and clamps as needed to make sure I my lines would stay safe and secure. You also must include a fuel injection rated fuel filter. For this I used a 2000 suburban fuel filter and Dorman fittings which screw into the filter. The "LS" and 8.1s have two different fuel rails. Early models used a return style fuel rail, and later models used a return-less style fuel rail. Mine fuel rail is a return style so I had to run 3/8 and 5/16 fuel lines from the tank to the fuel rail. So just run your lines accordingly and you're good to go. If you do have a returnless system, you'll want to use the common "corvette filter" which includes a regulator built into it.

2000 suburban fuel filter with Dorman fittings and Gates high pressure fuel line.

Corvette Filter for returnless fuel rails.

Other/Miscellaneous

Crank sensor. When the 8.1s were first released they had a certain type of crank sensor in them that had the connector at a bad angle for swaps in squares, and they had reliability issues. So definitely replace you crank sensor with an updated unit to alleviate those issues.

Updated Crank Sensor

Oil cooler bypass. The 8.1's came with an oil cooler. If you choose to delete the oil cooler like I did, You'll need to remove the oil cooler lines, and plug the holes in the block with 1/2"NPT plugs. In addition, you'll want to remove the bypass valve located above the oil filter. To do this, you'll need to remove the oil filter adapter that threads into the block. You'll need a 1/2" or 13mm Allen wrench to remove the adapter. I didn't have one so I welded some nuts to a bolt. I then inserted the bolt head into the adapter and used a wrench on the welded nuts. Once the adapter is unscrewed from the block, you'll need to use a 3/8" bolt and thread it into the valve. Once it's threaded in, you can pull the valve out from the block, and re-install the oil filter adapter.

On top, the bypass valve with a 3/8" bolt threaded into it to remove it from the block. Below that is my MacGyver solution for removing the oil filter adapter shown at the bottom right.

The oil filter adapter removed from the engine block with my home made 1/2" "allen wrench" used to remove it.

Battery/air box. This is an optional step, but it seemed like it would be about the same amount of effort as rigging it up a different way. The factory square body battery is on the passenger side. On the 8.1 and "LS" trucks, the battery is on the driver side and the factory air filter housing is on the passenger side. I wanted to retain the factory air filter housing/air duct from the housing to the throttle body. This meant I had to relocate the battery to the driver side. I did this using a factory dual battery tray setup which can still be bought new. With the new, driver side battery tray installed, I now had clearance to mount the 8.1 air box to the original passenger side battery tray using some home made metal brackets. This also allowed for use of the factory air duct. Another benefit of moving the battery to the driver side, is that it allows use of the factory 8.1 battery cables. I also chose to mount my ecm off of the side of the newly installed driver side battery tray using a combination of a home made bracket and a factory ECM mount.

ECM Mounted to auxiliary Battery Tray

Battery in Auxiliary Tray

Air Box Mounted to Original Battery Tray

Oil pressure gauge. The oil pressure sending unit is located at the rear of the engine next to the crank sensor behind the intake manifold. The block is threaded 1/4"NPT. You might have to get creative with adapters and angles depending on your square body oil pressure sending unit. Most square body oil pressure sending units are 1/8th NPT. If you have a mechanical oil pressure gauge like mine, You'll just need a 1/4NPT to 1/8th NPT adapter, and you can screw your oil pressure gauge fitting/line into that and be done. Some later model square bodies with electric oil pressure gauges actually use the same resistance values as the factory 8.1 oil pressure sending unit, in which case you can just use the 8.1 sending unit and wire pigtail and connect your square body gauge wire to that and be good to go. I ended up using the 1/4NPT to 1/8th NPT adapter, a short brass extension, and then threaded my oil pressure fitting/line onto that. I used the extension to raise up the fitting a bit to help with installing the fitting/line as without the extension, it sits really low and would be difficult to get a wrench on once the engine is installed.

Oil Pressure Fitting for mechanical oil pressure gauge. Also Shwoing Crank sensor.

Temperature gauge. The 8.1 uses only one temperature sending unit. This unit feeds information to the ECM. The temperature gauge gets its information directly from the ECM. This method wont work for the square body gauge. The 8.1 uses a three wire temperature sensor located on the passenger side head. Two of the wires go to the ECM. The third is not used from the factory but supports a temperature gauge and we can use that third wire for our square body gauge. Around 79-81 The resistance values that the temperature gauge uses changed from one value to another. The later model gauge is the one that uses the correct value for the factory 8.1 third wire from the temperature sensor. If you have a temp gauge that is pre '79ish, and use that third wire, it will not read correctly. You can also just use your square body temperature sensor in the the spare port in the driver side head and run your factory temp gauge wire to that.

This plug in the driver side head can be removed and your original square body temp sensor can be screwed in.

Temperature sensor location. The two black wires go to the ECM and the green wire goes to the temperature gauge.

Throttle peddle/throttle body. The 8.1s came only with Drive by wire throttle bodies. So there is no throttle cable. It uses a throttle pedal that has a position sensor on it and the ECM reads that information and actuates the throttle body accordingly. First off, it is possible to switch these to a throttle cable style throttle body. Most any cable style throttle body off an "LS" engine will work. They are the same size as the 8.1 throttle body. There are other modifications required other than just bolting the throttle body on. You need to make sure you have an ECM that will support the Drive by Cable (DBC) throttle body, Have it tuned appropriately, a throttle cable bracket, and there are some clearance issues with the oil fill tube. Additionally you'll have to modify your wiring harness or ensure that you buy a harness that has DBC style ends on it. It's doable, and Dirty Larry's thread listed below in the resources section does a good job of explaining the finer details of the swap. From my research, I find that the only folks who have a real need to go to the effort of swapping to a DBC throttle body, are folks with manual transmissions. And even then, its mostly only an issue with low speed "rock crawling" type applications where the Drive by Wire (DBW) system can struggle.

For me and my situation, I decided just to stick with the fully electronic, DBW throttle body. They have proven to be very reliable, and after a tune, they have no discernable "lag" between throttle input at the pedal and the opening of the throttle body. The DBW system uses an electronic throttle pedal, which sends throttle pedal position to the Throttle Actuator Control (TAC) module, Which correlates information with the ECM, to control the throttle body itself. There is a very common approach to this when swapping an 8.1 or "LS" into the square bodies which rectifies the problem of adapting an elecronic throttle pedal to the trucks. That is to use a 1998 chevy diesel truck throttle pedal. These pedals bolt directly in place of the original square body throttle pedal, but have an integrated throttle pedal postion sensor. So for me, I used the '98 diesel pedal, the 8.1 TAC module, and a pedal to TAC module harness from PSI.

TAC Module

Early Style Electric Throttle Body

1998 Diesel Bolt in throttle pedal

Conclusion

So, now that the swap is done, I can say it really is fairly straight forward. It is about the same amount of overall effort involved as doing an "LS Swap", But I'd say the 8.1 swap is a little bit easier on account of not having to use motor mount adapters and nothing special with the flex plate. Other than that, very similar.

This truck had a 350 when I got it. I swapped the 350 for a 5.3 shortly after I got the truck and that was about the 5th "LS" swap that I had done at that point. When I did the 5.3 swap, I did all the necessary accoutrement like the fuel injection style fuel tank, fuel lines, driver side battery conversion, air box mounted to passenger battery tray, ECM mount, ETC. So when I swapped the 8.1, I was actually swapping from a 5.3 to 8.1. The 5.3 was nice. It made the truck run great all the time and made it a great cruiser. But I wanted more. When I came across a good deal on an 8.1, I knew what I had to do. So I pulled the 5.3, sold it, and got to work on the 8.1. Because so much of the infrastructure was already there, it made the 5.3 to 8.1 swap super simple. Earlier I described the similarities between the 5.3 and 8.1. When it comes to power, there is no such similarity. The power is just so abundant on the 8.1 vs the 5.3. The 5.3 would screech the tires when flooring it from a stop. The 8.1 absolutely destroys the tires when flooring it from a stop. The engines run equally smooth and docile in every day driving. And honestly, about the fuel mileage, I might have lost 1mpg going to the big block. I think a lot of that has to do with this truck being a 2wd half ton. So for me, there were no drawbacks going from the 5.3 to the 8.1. It is my assertion that anyone who has a square body and is considering swapping in an "LS", should consider an 8.1 swap instead. Take any factory truck 454, and the 8.1 has more horsepower and torque than any of them. The 8.1 makes this truck absolutely move. I love it. And from now on, you'd be hard pressed to get me to want to swap anything but 8.1s.

The Truck

The 5.3 that was in the truck before the 8.1.

Removing the 5.3.

The 5.3 ready for it's new owner. The8.1 in the background.

8.1 Ready to be cleaned up.

8.1 Cleaned up and painted.

8.1 Set in place.

Completed 8.1 swap.

Parts I Used

(NOTE: Some of the following links are affiliate links.)

O2 sensor bungs:

https://amzn.to/3noUUSe

Upper Radiator Hose

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BBC lower radiator hose:

https://amzn.to/3nQ19Pj

5.3 Lower radiator hose:

https://amzn.to/3micirF

Radiator Hose Coupler

https://amzn.to/3nX4xrJ

Throttle pedal:

https://amzn.to/3M57qke

Throttle body gasket:

https://amzn.to/3mhcMhP

Valve cover gaskets:

https://amzn.to/3lMXIbH

Coolant crossover gasket(2x):

https://amzn.to/3no6wF6

Exhaust manifold gaskets:

https://amzn.to/3JVuuPB

Oil filter:

https://amzn.to/40RVgj5

Alternator:

https://amzn.to/3G1S8sJ

Starter:

https://amzn.to/3ZyD6Br

Starter bolt(2x):

https://amzn.to/3zfeALf

Serpentine belt:

https://amzn.to/3Kl3MBC

Fuel Filter:

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Fuel filter Fittings(2x):

amzn.to/3mkYa0U

Idler pulley:

https://amzn.to/3M3MJ8o

PSI Pedal To TAC Module Harness

1998 Diesel Bolt in Throttle Pedal(from PSI)

Resources

-By far the biggest square body 8.1 swap information resource is this thread on ck5.com made by DirtyLarry. His info was definitely instrumental in my swap as well as countless others.

L18 8.1L swap resource thread

-Raylar Engineering is the biggest aftermarket support business for 8.1 performance parts. The site also has a great deal of information about the 8.1s.

Raylar Engineering

-Richard Holdner is one of the only guys out there doing objective dyno testing on 8.1s(and so much more) and giving you all the details about what he's doing. Very much worth checking out his videos in general, but specifically his 8.1 videos in this instance.

Richard's Turbo 8.1 video

-Lawrence LT Tolman is likely king of the turbo 8.1s at this time. His 8.1 is swapped into a 2002 Silverado 1500, but the work he does on the 8.1 is very impressive and his channel is worth checking out.

LT's 800+whp dyno video

-If you would like to do your own harness rework like I did, all the information can be found at lt1swap.com. This is THE go to site for diy LS harness rework information. And, as stated above, the 8.1 wiring harness is essentially the same as an LS harness.

LT1swap

-Pete's Place Garage on youtube did an 8.1 swap into a 1990 suburban. His videos have a lot of good info on the swap.

Pete's Place Garage youtube

Amos Garcia Makes a great A/C compressor mount. He doesn't have a website, but I'll provide his email and YouTube channel.

Amospgarcia@gmail.com

https://youtube.com/@amospgarcia9152

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