Swap Shop: LS-Swapping A ’91 Suburban With The Aftermarket

As LS swaps have become more popular over the years, companies have invested time and money into the engine swap game. What used to be a massive puzzle of researching parts and components has turned into a bolt-on game of convenience. From ECU’s, engine and transmission mounts, exhaust systems, there is almost nothing you can’t find in the sea of swap parts. However, if you pick a car that is not as popular for an LS swap, you’ll have some challenges –but nothing like it would have been 10 years ago. 

For our swap, we chose 1991 Suburban, primarily because we had it, and the fact that it needed some help. The ’91 ‘Burb came equipped with the not-so-mighty Gen I 350 small-block Chevrolet engine. For ’91, Chevrolet rated the throttle body injection (TBI) engine at a pathetic 185 horsepower at 4000 rpm and 295 lb-ft of torque at 2400 rpm. The power numbers combined with a weight of 4,675-pounds were good for a 1/4-mile time in the high 16-second range at 80 mph. Add the fact that we are rolling on 35-inch tires, and this thing doesn’t have enough steam to safely pull out in front of any modern vehicle on the road. But we love it! And an LS swap will make all of our acceleration problems a thing of the past.

A short time ago, we did an article on Edelbrock’s Pro-Flo 4 EFI system. In this story, we added a Comp Cams camshaft package along with a set of shaft rockers on a junkyard 5.3-liter engine and dynoed it at KPE racing. With the new goodies, we were able to crank out 440 horsepower and 400 lb-ft of torque. If you haven’t connected the dots yet, this is the engine that we’re installing in the Suburban. This engine swap will more than double the power that we will have on tap in the 4×4, and also add over 100 lb-ft of torque to the combination.

Out With The Old

Our first order of business was to yank the 350 out of the engine compartment and make way for the new powerplant. There’s really nothing complicated about this process on an older vehicle, however, we had the archaic TBI system on the ’91, which forced us to chase a few wires, because we need to retain the electronic speedometer, water temp gauge, and oil pressure gauge. Luckily, we were able to find wiring schematics online that allowed us to trace out the wires, showing routing and color codes. 

While we were removing the engine, we decided to go ahead and swap the transmission, as well. The truck is equipped with a 700R-4 four-speed automatic transmission that is infamous for a problematic TV cable adjustment, which leads to transmission failures. With this in mind, we opted for a 4l80e transmission. On a two-wheel-drive Square Body, this transmission swap is a breeze. Holley offers a complete kit, including everything you need to do the conversion. The 4×4 version requires a little more finesse due to the NP241c transfer case, but more on this later.

With the engine and transmission out of the way, it was a perfect time to clean up the engine bay of the 28-year-old vehicle. At this time, we removed the unwanted wires, power-washed the engine bay, and gave it a new coat of satin black. We also went ahead wrapped what wires we could, but wanted to wait until the engine was installed before we finished up the wiring. We knew that we were going to be adding a few more wires to the harness and didn’t want to deal with removing the tape to add them. 

In With The New

The Hooker polyurethane mount inserts and engine mounts made bolting in the LS a simple task.

With the engine bay all cleaned up and the transfer case on the workbench, we decided to go ahead and install the engine and transmission. For the engine mounts, we used Hooker clamshell mounts (PN 71221004HKR), Hooker polyurethane mount inserts (PN 71221014HKR), and Hooker engine mounts (PN 12621HKR). They bolt on to the factory location with no problem. Holley offers a 2WD transmission cross member for use with the 4l80e in the Square Bodies, but we were unable to use it due to transfer case interference. Luckily, we were able to use the factory cross-member with just a minor modification, moving it back about 2-inches and drilling new holes. The engine and transmission fit in the Suburban perfectly…well, almost. We did have to modify the frame to clear the front driver’s side of the factory oil pan. This required a torch and the persuasion of a ball-peen hammer. 

After the engine was in place, this was an excellent time to get our cooling situation under control. We used the factory Suburban radiator, but we ditched the clutch fan system for electric fans. We chose to use dual 14-inch fans from GC Cooling. These units came with all of the mounting hardware needed along with heavy-duty wiring harnesses and relays. We followed the instructions and wired the fans to the Edelbrock Pro-Flo 4. The ECU will be able to control the fans independently of each other and allows the user to select the temperatures for fan activation.

Air Conditioning, No Sweat

Next, we moved on to a new dilemma: the A/C compressor. In 1991 the 350 small-blocks came with a serpentine drive accessory system. A single belt rotates the water pump, A/C compressor, alternator, and power steering pump. The LS also has a serpentine belt system, but the compressor is mounted low on the engine and uses a more modern Sanderson A/C compressor. The location of the compressor on the LS usually is not the best for a swap as it can interfere with the frame, steering, and other components. 

Holley offers an excellent conversion (PN 20-140) that uses the factory-style ’91 Suburban R4 compressor. This kit does a couple of things for anyone doing an installation on this model truck. First, it allows you to use the factory A/C lines and hardware without needing to modify anything, and mounts in the factory location. Second, you can run all of the factory LS accessories with the OEM mounts. Since we already had everything we needed with our 2004 LS junkyard motor, we were able to save some money and get the A/C compressor and bracket. You will need to order (PN 21-3), as well, if you use your existing truck accessories. A complete accessory drive like (PN 20-136) can also be used, which includes brackets, power steering pump, alternator, and A/C compressor.

Breathing Room

Instead of using the factory exhaust manifolds, we decided to go with a set of Doug Thorley Tri-y headers (PN THY-322Y-C). The Tri-Y’s primary tubes are 1-7/8-inch and made from 14-gauge steel. The pipes merge into a 3-inch collector and have a 3/8-inch thick flange. The finished product looks killer due to the construction and the silver ceramic coating, which will reduce underhood temperatures. The kit comes with all of the bolts, gaskets, and collector reducers for installation. 

Edelbrock Pro-Flo 4

If you haven’t read about the installation and dyno session with the Edelbrock Pro-Flo 4, you can read it here. This unit made some serious power on the dyno with very little tuning. We might have spent 10 minutes messing with the tune, and it was perfect. This unit is simple to program and easy to install. 

First, we mounted the ECU to the firewall and then plugged in the harness connectors. With this system, there are only a few wires that need to be hooked up for operation, power, ground, accessories, fuel pump, and electric fans, if required. We already had the system wired from our previous dyno session, aside from the oxygen sensor. We routed the sensor wires away from the headers and threaded the sensor into the header. At this point, the engine is ready to fire up. This was by far the easiest part of our swap, thanks to the simplicity of the Pro-Flo 4.

Houston We Have A Problem

Before we installed the transmission, we had a couple of things to address. The COMP Cams camshaft that we used might have been a little aggressive for our application, but who are we kidding –more power is better. To make sure the ‘Burb would idle properly in drive, we needed a higher stall speed. TCI had what we required with its billet torque convertor. This unit will hold up to our LS with no problems and will bump the stall speed to around 2,300 rpm. This unit will not only allow our four-door hauler to stay running at idle, but it will also help to get the massive beast rolling from a dead stop.

The new TCI torque convertor would not bolt up to our factory 5.3-liter flexplate without enlarging the holes, so we called ICT Billet to see what the best options were. The guys recommended (PN 551356X), which is a PRW unit that is SFI 29.1 certified. They also suggested the converter hub flexplate crankshaft adapter (PN 551165). This hub allows the 4L80e convertor to center itself in the flywheel and will alleviate any movement or vibration with the torque converter upon acceleration or deceleration, thus avoiding transmission damage.

ICT Billet saved the day when our 4l80E torque convertor would not bolt up to the 5.3 flexplate. We got an SFI approved flexplate, flexplate crankshaft adapter, and sensor adapters from the company.

With parts in-hand, we torqued the supplied bolts down in conjunction with the converter hub flexplate crankshaft adapter. 

 

Rockland Standard Gear (RSG) was able to supply us a 32-spline input shaft and bearing which allowed us to bolt the NP241C transfer case to the 4L80E transmission. This conversion was a simple process that can be done by most gearheads in their garage. You can see the size difference between the factory 27-spline and the 32-spline unit in the images.

Second, the NP241c transfer case operates off of a 27-spline shaft in the 700R-4. The output shaft on a 4L80e is a 32-spline unit. For this problem, we called Rockland Standard Gear to see what we needed to do. Rockland supplied us with a new bearing and a 32-spline input shaft to mate up with the 4L80 output. We dismantled the case and installed the new bearing and input shaft. After we got it all reassembled, we bolted it back on the transmission. This process was easier than we had expected thanks to the outstanding tech support from Rockland Standard Gear. 

Third, the Pro-Flo 4 that we used will not support an electronically shifted transmission (stay tuned for a new product from Edelbrock that will address this problem) — so we needed a TCU that would take care of shifting duties. We got in touch with TCI and ordered the EZ-TCU. This controller allows for maximum control over shift points, shift firmness, shift speed, and is ready to go right out of the box. The unit is also fully programmable based on load, speed, and RPM. TCI just released a wireless version of the EZ TCU (PN 302600) allowing you to connect and tune the controller via Bluetooth. The app is easy to use and just super cool. With the Bluetooth capabilities of the Edelbrock Pro-Flo 4 and the EZ-TCU, we can monitor our drivetrain by way of our dash-mounted tablet. 

The installation of the EZ-TCU is simple and you can read more about it here. The unit includes a custom wiring harness that plugs into the factory connectors of the transmission. All we needed to do was mount the unit, connect to a clean tach signal, and wire in a TPS wire. When we were done with these steps, we joined via Bluetooth to the module and programmed the TCU.

Fuel It

The first picture shows the difference between the '87 sending unit in comparison to our '91. Luckily, we were able to take what we needed off of the Holley unit and use the components on the factory sending unit. We also mounted the Edelbrock fuel pressure regulator on the firewall.

For the fuel system, we turned to Holley for its drop-in pump and sending unit (PN 12-308). Unfortunately, the ’91 Suburban’s fuel system is entirely different than the previous 1973-87 trucks that the pump was designed to fit. The good news is that since the ‘Burb was already a fuel-injected unit, we just needed to swap the fuel pump and wiring. We already had  high-pressure and return lines to use, making plumbing a breeze. The next step was to mount the Edelbrock fuel pressure regulator (PN 1729) on the firewall, connect the lines, and set the fuel pressure for 58-pounds. 

Just Add Oil

We were finally in the home stretch and just need to button everything up. For lubrication, we chose to go with Torco 10w30 weight, since our 5.3 has over 100,000 miles on the clock. Torco SR-1 is a 100-percent synthetic racing oil that is engineered to protect the engine even in extreme conditions. We also like the fact that Torco oil can provide more horsepower and torque due to minimal friction. 

Crank It Up

After we added all of the fluids, checked vacuum lines, and made sure the hose ends were tight, it was time to fire the engine up. To do this, we went through the setup wizard on the Edelbrock Pro-Flo 4 tablet and answered a few simple questions. The tablet then transfers the data via Bluetooth to the ECU. We are also able to use the tablet to monitor the engine’s vitals in real-time while we drive. At this point, the system was ready to go. We hit the ignition switch, and immediately the 5.3 roared to life. The Comp Cams camshaft thumped away as the exhaust was sent out the Doug Thorley headers and Flowmaster mufflers.

 Driving Impressions

The 5.3-liter LS and 4l80e completely transformed the driving characteristics of the Suburban. The additional torque of the LS gets the heavy-weight off the line while the extra horsepower makes it a dream when dealing with passing slower-moving cars and merging with cars via on-ramps. It’s a completely different vehicle. While we love the added power of the engine combination, we also like the Bluetooth connectivity of the Edelbrock Pro-Flo 4 and TCI transmission controller. This wireless feature makes it easy to change the tune in the engine and transmission in a matter of seconds. You can also keep tabs on the engine and transmission vitals while rolling down the road.

Conclusion

Our LS installation was pretty straightforward, but any engine swap that you perform is going to have its share of issues. It could be a result of a lack of parts, wiring woes, uncharted territory, or any number of things. Just remember to expect the unexpected, and the odds that you can do an LS swap in a weekend are not very likely. Take our word for it. 

 

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About the author

Brian Havins

A gearhead for life, Brian is obsessed with all things fast. Banging gears, turning wrenches, and praying while spraying are just a few of his favorite things.
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