Swapping a 5.9L Cummins into A 1973 to 1991 Suburban

Doomsday Diesel Part 1 Pulling The Motor

Our Doomsday Diesel buildup began with a ¾-ton GMC Suburban that’s based on the ’73 to ’87 GM pickup. These trucks are caveman simple, all steel, and every part you could need is available from the aftermarket. We found our ’91 with 200,000 miles for $2,400. The first step was to pull the gas engine and sell it on eBay.

Our Doomsday Diesel buildup began with a ¾-ton GMC Suburban that’s based on the ’73 to ’87

In 2012, the world isn’t going to end, zombies aren’t going to attack, and there won’t be riots in the streets. But if it does, they do, or there are—we’ll be ready!

In the next 12 issues, we’re going to build a diesel vehicle for maximum survivability in the worst possible scenarios. We’re going to create a simple truck that exploits the versatility, durability, and efficiency diesels offer. The Doomsday Diesel Suburban will be part getaway car and part urban-assault vehicle. It’ll have all-terrain capability, a 1,000-mile fuel range, and enough room to carry a small squad of survivors.

We begin this month by bolting a ’95 5.9L Cummins into a ’91 ¾-ton GMC Suburban. This swap has been done many times, but our plans call for using a GM transmission close to the factory location, removing as little of the frame as possible, and retaining the ’94 to ’98 Cummins fan. To help us with the project, we’ve enlisted Mercenary Offroad in Camarillo, California.

Doomsday Diesel Part 1 Engine Cradle Installed

We chose this bolt-in engine cradle from Screamin’ Seeman Off Road (SSOR) because it uses ’03 to ’07 engine mounts and ties into the frame just as the stock crossmember did. Its C-channel design (arrows) is fully adjustable and only requires the truck to have a 2½-inch suspension lift to prevent oil-pan-to-axle interference. We drilled out four rivets, removed the factory crossmember from the frame, and temporarily mounted the SSOR cradle.

We chose this bolt-in engine cradle from Screamin’ Seeman Off Road (SSOR) because it uses

In the months ahead, we’ll plumb, wire, and create an exhaust for our Cummins. We’ll also reinforce the chassis, beef up the drivetrain, and upgrade the interior to keep our Sub on the road for years to come. When we’re done, we’ll have a vehicle that’ll not only be a blast to drive, but one that’ll keep us safe and sound come December 21, 2012—no matter what the Mayan calendar says might happen.

The ’95 12-valve we bought for $1,200 didn’t come with a transmission, but thankfully our ’91 Suburban had a heavy-duty 4L80E four-speed automatic. Using a Destroked 6061 billet-aluminum adapter plate and SFI-approved steel flexplate, we bolted the Cummins directly to the 4L80E.
The ’95 12-valve we bought for $1,200 didn’t come with a transmission, but thankfully our
To give the Destoked adapter a corrosion-proof finish, we had Prime Plating hard anodize it. This is the same Type III process high-end cookware receives, and the finish should outlast the truck. We reused seven of the 15mm Cummins bolts and torqued them to 57 ft-lb. The eighth bolt was replaced with an Allen-head bolt provided by Destroked (arrow).
To give the Destoked adapter a corrosion-proof finish, we had Prime Plating hard anodize i
Adapting the Cummins to a 4L80E also required a new Destroked flexplate. This steel, SFI-approved piece was bolted on using the original Cummins clamp ring and 19mm crankshaft bolts, which were torqued to 101 ft-lb.
Adapting the Cummins to a 4L80E also required a new Destroked flexplate. This steel, SFI-a

We chose the 5.9L for its million-mile durability—even at our projected 375 to 475hp power level. We knew we’d need a transmission that could keep up, so we’re working with TCI to test its 4L80E-based, 6X Six Speed that’s rated for up to 850 hp. By leveraging TCI’s transmission expertise, proven electronic controls, and hot rod experience, we have a package we know will work right—every time.
We chose the 5.9L for its million-mile durability—even at our projected 375 to 475hp power
We used ARP 12-point stainless-steel fasteners to bolt the TCI 6X automatic between our Cummins and BorgWarner 4470 transfer case from a ’98 1-ton GM dualie. This transfer case is stronger than the NP 241 and NP 208 that came in Suburbans, features a power take-off (PTO) capability and 1410 rear driveshaft yoke, and bolts right up to the close-ratio TCI six-speed using the cast-iron adapter that came with our ’91 Suburban.
We used ARP 12-point stainless-steel fasteners to bolt the TCI 6X automatic between our Cu
The SSOR Cummins swap kit includes two ’03 to ’07 5.9L Cummins passenger-side cast-iron motor mounts. The driver-side mount is moved into the correct location using an adapter plate (arrow), which relocates the mount 1 1/2 inches back on the engine.
The SSOR Cummins swap kit includes two ’03 to ’07 5.9L Cummins passenger-side cast-iron mo

With the motor mounts and ’03 to ’07 rubber isolators bolted to the engine, Mercenary Offroad’s Todd Farrand swung the engine, transmission, and transfer case into place using a 2-ton engine hoist. Our plan was to bolt the transmission back into the stock location, and that would dictate where the Cummins would go.
With the motor mounts and ’03 to ’07 rubber isolators bolted to the engine, Mercenary Offr
The ’73 to ’91 Suburban engine compartment is very similar to the ’89 to ’93 Dodge, so a Cummins fits well in these trucks. Still, we made sure there was enough room between the turbo outlet and the heater box (A), there was at least 1 inch between the firewall and the rear of the engine (B), the intake and the brake booster didn’t hit (C), and the mechanical fan didn’t contact the radiator (D).
The ’73 to ’91 Suburban engine compartment is very similar to the ’89 to ’93 Dodge, so a C
The cooling fan on our Cummins hit the four-core radiator that was installed in our truck (a thinner two-core was stock). So we changed the fan, pulley, and iron mount out for the parts used on an ’89 to ’93 Cummins Dodge (arrow). They bolted right up and moved the fan nearly 2 inches away from the radiator. But now we’ve decided to move the entire drivetrain rearward in the frame 2 inches and fit the truck with a narrower two-core aluminum radiator. We chose this route because we think the ’94 to ’98 fan will pull more air through the radiator because it isn’t squashed up against the engine, like the ’89 to ’93 fan is.
The cooling fan on our Cummins hit the four-core radiator that was installed in our truck

There were three areas the Cummins didn’t fit in our Suburban: 1) the Dodge A/C compressor hit the passenger side of the frame, 2) the SSOR crossmember had 1-inch of clearance before it hit the differential, and 3) the front of the oil pan and harmonic balancer hit the crossmember. We plan to 1) use a different A/C compressor to prevent having to cut the frame, 2) we’ll raise the truck with 4-inch lift springs to clear the SSOR crossmember, and 3) we’ll remove as little metal from the frame (note our cut line) as possible to clear the balancer.
There were three areas the Cummins didn’t fit in our Suburban: 1) the Dodge A/C compressor
You can push the Cummins further back in the chassis to give the balancer and A/C compressor more room, but no matter what you do, you have to cut either the firewall or the frame. We trimmed a 13-inch oval out of the frame and used a tape measure to make sure the crankshaft was centered in the truck. We then verified the rear yoke on the transfer case was also centered in the chassis. You can bias the engine to one side or the other to get more room for the exhaust, A/C, or brake booster—just make sure the engine isn’t sitting crooked in the frame by more than 1/4 inch.
You can push the Cummins further back in the chassis to give the balancer and A/C compress
Our final step was to confirm the engine was tilted 5 degrees down in the rear for optimal driveshaft angle using an angle meter from Home Depot (A). Then we drilled the SSOR C-channel mounts to fit four 1/2-inch bolts through the factory motor-mount holes in the frame (B). We also drilled four new holes in the frame where the transmission crossmember now sits.
Our final step was to confirm the engine was tilted 5 degrees down in the rear for optimal

SOURCES
ARP 1863 Eastman Avenue Ventura CA 93003 800-826-3045 www.arp-bolts.com	TCI Auto 888-776-9824 www.TCIAuto.com
Destroked 7245 W. 116th Place Broomfield CO 80020 303-945-7570 www.destroked.com	Screamin Seeman Off Road 18476 Eiler Ave Faribault MN 55021 507-330-3567 www.screaminseeman.com
Mercenary Off Road Sun Valley CA 91352 www.mercenaryoffroad.com