1991 GMC Suburban: Doomsday Diesel Part 7 Photo Gallery
Plumbing, Cooling, and Power Generation
David Kennedy –
Nov 1, 2012
Photo 1/24 | doomsday Diesel Part 7 suburban On Lift | 1991 GMC Suburban: Doomsday Diesel Part 7
Photo 2/24 | doomsday Diesel Part 7 suburban On Lift | 1991 GMC Suburban: Doomsday Diesel Part 7
Photo 3/24 | doomsday Diesel Part 7 engine Acessories Installed | The 5.9L Cummins fits the frame of ’73 to ’91 solid-axle GM trucks well, but fitting the A/C compressor is a challenge. Dodge mounted its Sanden compressor low on the engine, and it hits the frame. We moved the compressor’s mounting location using a Cummins water inlet housing and compressor mount (A) from a ’95 Ford F-800 (Cummins PN 3930888). We sealed it to the engine with a new square-cut water inlet gasket (PN 3906697). This solved one problem and caused new ones. We then needed the tensioner mount plate (B) to bolt to the compressor mount (Cummins PN 3930838) and had to find a way to mount an alternator. We bought a new Sanden compressor (PN 4666) and belt tensioner (D) to replace the worn Dodge piece (Cummins PN3978021), though you could reuse the Dodge part. We decided to upgrade to the heavy-duty truck alternator the Ford F-800 used. By adding the lower alternator mount (C) to our engine (Cummins PN 3930820), we were able to bolt on a 200-amp Delco-Remy 28SI alternator that dwarfs the alternator Dodg
Photo 4/24 | doomsday Diesel Part 7 temperature Sensor On Torque Convertor | Moving under the truck, the TCI 6X six-speed (based on a GM 4L80E) transmission was fitted with a Precision Industries triple-disc converter. The lock-up converter was tuned for the Cummins powerband and features a billet-steel front cover for durability. We bolted it to the Destroked flexplate using ARP bolts (PN 230-7305), which we torqued to 35 ft-lb. You’ll also note we fit the torque converter with a Thermax temperature recording sticker, which will tell us the peak temperature the converter experiences.
Photo 5/24 | doomsday Diesel Part 7 transmission Pan Install | To keep the transmission temperatures down and add rigidity to prevent transmission case flex, Mercenary Offroad’s Todd Farrand added this Mag-Hytec cast-aluminum transmission pan. It features a flush-mounted drain plug, an O-ring gasket around the mating surface, and cooling fins to dissipate heat. Sharp-eyed readers will also see that Farrand fit a 4-inch downpipe to our Suburban—we’ll show you how next month.
Photo 6/24 | doomsday Diesel Part 7 torque Wrench With Box End Wrench | We couldn’t fit our torque wrench between the Cummins’ oil pan and the flexplate, so to torque the 10mm ARP torque converter bolts, we used a box-end wrench to extend the reach of our torque wrench. By fitting the 12-point, 7⁄16-inch end over the 3⁄8-inch-drive torque wrench, we tightened the flexplate bolts to 35 ft-lb using the 1/2-inch side of the wrench. Technically, the ARP bolts have 13mm heads, but the 1/2-inch wrench fit tight enough. Using the formula M1 = M2 x L1 / L2, where: M1 is the torque setting of the wrench, M2 is the actual torque applied to the nut, L1 is the normal length of the wrench, and L2 is the extended length of the wrench—we found that using our 18 1/2-inch-long toque wrench with our 7 1/2-inch-long box-end wrench meant that we’d set the torque wrench to approximately 25 ft-lb to torque the bolts to 35 ft-lb.
Photo 7/24 | doomsday Diesel Part 7 torque Converter Cover | We bolted the ’91 Suburban’s 4L80E torque converter cover back into place after Farrand ground off the lip (arrow) that used to mate up against the Chevy small-block’s oil pan.
Photo 8/24 | doomsday Diesel Part 7 dipstick Tube | We couldn’t use the factory 4L80E dipstick tube because we’d moved the transmission and engine 1 1/2 inches closer to the firewall. The TCI dipstick tube (PN 743805) cleared the firewall without any problem, but it placed the locking dipstick handle next to the exhaust manifold (arrow).
Photo 9/24 | doomsday Diesel Part 7 legthened Dipstick Tube | We couldn’t use the factory 4L80E dipstick tube because we’d moved the transmission and engine 1 1/2 inches closer to the firewall. The TCI dipstick tube (PN 743805) cleared the firewall without any problem, but it placed the locking dipstick handle next to the exhaust manifold (arrow).
Photo 10/24 | doomsday Diesel Part 7 mounting Intercooler | From day one, we knew we wanted to run BD Power’s Cool-It intercooler (PN1042520), because its micro-extruded-tube design offers superior strength compared to the typical stuffed-tube coolers Dodges came with. BD Power’s Cool-It tubes have a 0.025-inch wall thickness that’s been tested to withstand 400 psi. So the challenge for us became fitting this prime piece into our GMC’s grille. Using cardboard to prevent damage to the BD Cool-It intercooler, Farrand mounted it to the front of the GMC’s radiator support. It turns out the quad headlight option used on these trucks (’89 to ’91) doesn’t allow enough room for intercoolers designed for ’94 to ’02 Dodge Rams. We called LMC Truck and ordered the headlights, blinkers, and trim pieces for the ’89 to ’91 work truck grille. This front end was designed around 5x7-inch headlights and smaller blinkers. We assumed the 5x7-inch headlights would bolt right on to our existing radiator support—but believe it or not, the work truck grille requires a unique radiator support
Photo 11/24 | doomsday Diesel Part 7 trimmed Lower Grill Support | To mount the BD Power Cool-It intercooler we bought the upper and lower mounts from a local Chrysler parts department. Farrand made two brackets to attach the BD intercooler to the bottom of the GM radiator core support. We’ll show you how he did it next month, as we need to get a different core support anyway. One thing we can show you this month is that the lower grille support had to be cut out (arrows) to fit the BD intercooler. A stock ’94 to ’02 Ram intercooler would’ve probably fit OK. We think the Cool-It intercooler is stout enough to be our truck’s grille, but we’ve got plans for fitting a doomsday-ready GMC grille over it just the same.
Photo 12/24 | doomsday Diesel Part 7 cummins Engine Installed | The Cummins looks surprisingly at home in the GMC’s engine compartment. It appears we’ll be able to use ’94 to ’98 12-valve intercooler tubes, hoses, and clamps to mate the engine to the BD intercooler. We also found LMC Truck’s upper radiator mount for a 454-powered Suburban (PN 32-0988) fits perfectly and protects the top of the radiator when we have to work in the engine compartment.
Photo 13/24 | doomsday Diesel Part 7 radiator Installed | Here’s why protecting the radiator is so important to us. To keep the Cummins cool no matter what, we contacted Be Cool in Essexville, Michigan, to get its high-performance twocore direct-fit radiator (PN 80313) module. This radiator is part of a cooling module that’s designed to handle engines making 1,000 hp, so it’ll be perfect for our truck. To make engine swaps easier, Be Cool can even build this radiator with 1 3/4-inch inlet and outlets to match the hose size Dodge used for this engine. Using the LMC Truck upper radiator support, we literally bolted the Be Cool radiator in place using LMC’s rubber isolators (PN 32-0972).
Photo 14/24 | doomsday Diesel Part 7 fan Clutch Clearance | Be Cool designs its cooling modules to use electric fans because they allow for 100 percent operation when the engine is idling. That’s great for us, because we didn’t have enough radiator-to-fan clearance to fit the ’94 to ’98 Cummins mechanical fan. By using the ’89 to ’93 Cummins fan (which moves the fan 2 inches closer to the engine) we could probably make it all fit.
Photo 15/24 | doomsday Diesel Part 7 cummins Engine Installed | The Cummins looks surprisingly at home in the GMC’s engine compartment. It appears we’ll be able to use ’94 to ’98 12-valve intercooler tubes, hoses, and clamps to mate the engine to the BD intercooler. We also found LMC Truck’s upper radiator mount for a 454-powered Suburban (PN 32-0988) fits perfectly and protects the top of the radiator when we have to work in the engine compartment.
Photo 16/24 | doomsday Diesel Part 7 intake Tube Installed | We thought we might be able to bolt on an air intake designed for the Cummins in a ’95 Ram, so we ordered K&N’s 57-Series Generation II intake (PN 57-1525). The intake tube coupled with the Industrial Injection turbo perfectly, cleared the massive 28SI alternator, and would have fit perfectly—if our truck didn’t have A/C. Not to worry, we know we’ll find something in K&N’s catalog that we can make fit.
Photo 17/24 | doomsday Diesel Part 7 battery Tray Installed | With the front clip back on the truck, it was time to test fit LMC Truck’s driver-side battery tray. This piece was used on ’82 to ’91 trucks that were equipped with 6.2L diesels to mount a second Group 34 battery in the truck. Though GM has discontinued this part, LMC continues to build and sell it (PN 38-6318).
Photo 18/24 | doomsday Diesel Part 7 odyssey Battery Installed | While two Group 34 batteries provide a lot of power, we’re building this truck for Doomsday—and we need as much electrical reserve as possible. When it comes to nukeproof 12-volt power, nothing can compete with the steel-jacketed, drycell, absorbent glass mat (AGM) Odyssey batteries. These batteries were originally designed for use in commercial vehicles and boats. They are roughly 2 inches taller, 2 inches longer, and 28 pounds heavier than a Group 34 Odyssey battery—but they pack more lead, offer 1,150 cold-cranking amps (300 more than the Group 34 battery), and have a 205-minute reserve capacity. They don’t quite fit on the factory battery trays yet, but we’ll fix that, too.
Photo 19/24 | doomsday Diesel Part 7 fuel System Plumbing | Our Suburban began life as a gas tuck, so we pulled the factory tank and replaced it with a 40-gallon diesel tank from LMC Truck (PN 32-5950). We originally planned to use LMC’s factory-style diesel fuel sending unit (PN 32-4072), but after talking with various electric lift pump suppliers, we deemed the 5⁄16-inch pickup tube way too small. We decided to plug the factory fuel pickup (A) and fuel return (B), and replace them with a -10AN fuel pickup (C) and fuel return (D). The -10 AN size Earl’s fittings mate with a 5⁄8-inch outside diameter stainless-steel seamless tube, which in our case meant the inside diameter of the new fuel pickup and return are 0.59 inch. That’ll give our Industrial Injection P-pump plenty of fuel. To reduce fuel foaming and give the returned fuel time to cool off, we designed the fuel return tube to dump the diesel in the rear corner of the tank.
Photo 20/24 | doomsday Diesel Part 7 fuel Pickup Tube | Our tank’s new fuel pickup and return were made possible by drilling two 3/4-inch holes in the top of the LMC Truck tank. We blew the tank out with compressed air and used Parker Stat-O-Seals (arrow) to seal the Earl’s aluminum bulkhead fittings to the top of the tank. We installed our new fuel pickup and return through the factory opening in the tank.
Photo 21/24 | doomsday Diesel Part 7 fuel Bulkhead Fitting | Parker’s website says you only need to use the Stat-O-Seals on one side of bulkhead fittings, but we used two per fitting for an extra layer of insurance. To prevent the AN nut from loosening (arrow), we added a few drops of Loctite 545 thread sealer.
Photo 22/24 | doomsday Diesel Part 7 fuel Filter Mock Up | We installed the tank using LMC Truck’s tank straps (PN 32-5823), and anti-squeak kit (PN 32-5816). Then Farrand designed a set of mounts for two Nicktane fuel filters using cardboard to make templates.
Photo 23/24 | doomsday Diesel Part 7 cat Filter Mounted To Bracket | He then drew the mounts on his computer and had a local water-jet shop cut the plates out of steel. After he confirmed the fit, Farrand TIG-welded the steel filter mounts together and added a reinforcement gusset to handle the additional weight of the filter when it’s full of fuel.
Photo 24/24 | doomsday Diesel Part 7 fuel Filter And Water Seprteator Installed | The way we designed our fuel system, diesel will flow out of the tank and into a Nicktane water separator before it is drawn into a Fuel Lab Prodigy electric lift pump on the framerail (not installed here). The fuel will then flow out of the pump and into a 2-micron Cat fuel filter before being routed to the P7100 injection pump.