Atlas Transfer Case Guide: Race vs Standard for Ultra4 Builds
If you are building an off-road race car, a rock crawler, or a trail rig that needs to survive the worst terrain on the planet, the transfer case is the heart of your drivetrain. It connects the transmission to your axles, distributes power to all four wheels, and gives you the gear reduction you need to crawl over boulders at idle or blast across open desert at speed. Get it wrong and your build is dead on the trail. Get it right and you have a drivetrain that will take abuse for years without flinching.
At Bomber Fabrication, the Atlas 2-speed transfer case by Advance Adapters has been the only transfer case we trust in our race cars for over a decade. Randy Slawson has run an Atlas in every one of his four King of the Hammers wins (2013, 2015, 2021, and 2026), and every Bomber Race Chassis we ship leaves the shop with Atlas mounting provisions built in. This is not a sponsorship talking point. It is a decision backed by hundreds of hours of seat time at the toughest single-day off-road race on earth.
This guide covers everything you need to know before buying an Atlas transfer case: race case versus standard duty, gear ratio selection, fitment, pricing, and the real-world lessons we have learned building and breaking these cases in Johnson Valley. We typically keep both race and trail Atlas cases in stock with no lead time, so when you are ready to build, the case is ready to ship.
What Is the Atlas Transfer Case?
The Atlas is an all gear-driven transfer case manufactured by Advance Adapters. First introduced in 1995 and continually refined over three decades, it has become the industry standard for serious off-road builds ranging from daily-driven trail rigs to fully unlimited Ultra4 race cars. Unlike chain-driven OEM transfer cases, the Atlas uses helical-cut gears supported by needle and taper roller bearings, which means no chains to stretch, no plastic guides to wear out, and significantly more strength under load. With over 30,000 units sold, the Atlas name is synonymous with off-road performance.
The Atlas is available in two mounting configurations: direct mount (married) and divorced. A direct mount Atlas bolts directly to the back of your transmission using a vehicle-specific adapter housing, just like a factory transfer case. This is the most common setup and is what we run in every Bomber race car. A married Atlas eliminates the need for a third driveshaft between the transmission and transfer case, which means fewer failure points, less rotating mass, and a simpler drivetrain. For custom tube-frame builds like ours, it also keeps the chassis packaging clean and tight.
The divorced configuration mounts the Atlas independently on the frame, connected to the transmission by a short driveshaft. Divorced setups have their place in builds where a direct-bolt adapter is not available for the specific engine/trans combination, or where the builder needs maximum flexibility in driveline angle optimization. The divorced Atlas requires three yokes (input, front output, rear output) and a frame-mounted crossmember, and is available in right or left drop configurations.
The case itself is machined from 356-T6 heat-treated aluminum, weighs approximately 110 pounds dry, and accepts roughly two quarts of GL-4 synthetic gear oil. It is a fully synchronized, shift-on-the-fly design, meaning you can engage and disengage low range without stopping the vehicle. Twin-stick operation gives you independent control of front and rear outputs: 2-HI, 4-HI, RWD-Lo, FWD-Lo, and 4WD-Lo.
Because every Atlas is custom built to order, you choose your gear ratio, input spline count, output shaft configuration, vehicle-specific adapter, and mounting style. Advance Adapters offers vehicle-specific Atlas kits for Jeep TJ, JK, JL, YJ, CJ, Cherokee XJ, ZJ, Ford Bronco, Toyota Tacoma, Tundra, T100, and FJ Cruiser, plus universal configurations for custom builds. This is not a one-size-fits-all catalog part. It is a purpose-built component tailored to your drivetrain.
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The Advance Adapters Atlas 2-speed transfer case. Helical-cut gears, 356-T6 heat-treated aluminum case, and BorgWarner synchronizers. Available fully built from Bomber Fab. We keep race and trail cases in stock. |
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Atlas Race Case vs Standard Duty: What Is the Difference?
This is the question we get asked the most. Advance Adapters builds two tiers of the Atlas 2-speed: the Trail Series (standard duty) and the G2 Pro Series (race case). Both use the same external 356-T6 aluminum case and the same basic architecture. The difference is inside the case. The G2 Pro Series was designed specifically for heavier Gross Vehicle Weight Ratings (GVWR) and high-horsepower race applications. The upgrade to a 1-1/2" idler shaft assembly delivers 109% more beam strength, a 7% increase in dynamic (and 15% static) load-rated bearing capacity, 25% more thrust surface area for high-torque situations like rock crawling and heavy towing, and a 7% reduction in weight compared to the previous design.
When to Choose the Trail Series
If you are building a weekend trail rig or a daily driver that sees moderate to hard wheeling, the Trail Series Atlas is more than enough case. The standard 8620 shafts and 1.25" idler will handle anything short of sustained high-horsepower abuse. Most Jeep, Bronco, and Toyota trail builds run a Trail Series 4.3:1 or 3.8:1 and never look back. Pair it with a solid set of Spidertrax axles and lockers and you have a drivetrain that will outlast the body of your truck.
When to Choose the Race Case
If your build sees competition, sustained high RPM desert sections, or you are running north of 500 horsepower, the G2/G3 Pro Series race case is the move. The 300M output shaft is drastically stronger than the standard 8620, and the super-finished gears run cooler and shed heat faster under load. Every Bomber Race Chassis we build for KOH competitors gets a fully built Atlas race case married directly to the transmission. At King of the Hammers 2026, Randy Slawson ran a 2.0:1 race case with 300M shafts, and it survived over 13 hours of the most brutal course in KOH history without a single transfer case issue.
You can order the Atlas race case fully built from Bomber Fab starting at $4,225.96. We typically keep both race and trail cases in stock, so there is no lead time on most configurations. We also carry the Atlas standard duty transfer case for trail and budget builds.
Atlas Transfer Case Gear Ratios Explained
Choosing the right gear ratio is one of the most important decisions in your build. The Atlas low range ratio multiplies the gear reduction from your transmission and ring-and-pinion, which directly affects your crawl speed, your desert cruising RPM, and how hard your brakes have to work to stop the vehicle in gear. Here is a breakdown of every ratio Advance Adapters offers and where each one fits best.
Pro tip from the shop: Your total crawl ratio is your transmission first gear ratio x transfer case low range ratio x ring-and-pinion ratio. If you are running a 4L80E with a 2.48 first gear, a 2.0:1 Atlas, and 4.56 axle gears, your crawl ratio is roughly 22.6:1. That is plenty for KOH-level rock trails with 40" tires. If you need help dialing in your gearing, give us a call. We have built hundreds of these combinations and can tell you exactly what works for your setup.
Why the Atlas Transfer Case Dominates Ultra4 Racing
King of the Hammers is not like any other race. You are running wide-open desert at 100+ MPH one minute and crawling up a vertical rock wall the next. Your transfer case has to shift cleanly between high and low range dozens of times in a single race, absorb the shock loads of landing off rock ledges, and survive sustained heat from hours of desert sections. Chain-driven cases do not last in this environment. Period.
A Bomber Fabrication race car attacking the Johnson Valley desert. Every Bomber runs a married Atlas 2-speed transfer case.
The Atlas has won more King of the Hammers races than any other transfer case. It is the transfer case of choice for Randy Slawson, a 4x KOH champion and the only driver to compete in all 20 King of the Hammers races since the inaugural event in 2007. The cars we build at Bomber Fabrication run a married Atlas paired with a Art Carr/Winters 4L80E shifter and full Spidertrax axle assemblies with Spidertrax knuckles. Our ECU Master dashes monitor every vital in real time so we know exactly what the drivetrain is doing at all times. That combination has put us on the podium at KOH more times than we can count.
"We were a lap-and-a-half or two laps in, running in 12th, and having problems. But the Atlas never quit. We had to replace two power steering rams during the race, but the drivetrain just kept going."
-- Randy Slawson, 4x King of the Hammers Champion, Bomber Fabrication
Atlas Transfer Case Mounting and Installation
How you mount your Atlas depends on your build. In our Bomber race cars, we run the Atlas as a direct mount (married) transfer case that bolts directly to the back of the transmission. There is no third driveshaft between the trans and the transfer case. This is the cleanest, strongest configuration and it is what has won us four King of the Hammers titles. The married setup eliminates a failure point, reduces rotating mass, and keeps the drivetrain as compact as possible inside our tube-frame chassis.
For OEM-platform vehicles like Jeep Wranglers, Broncos, and Toyota trucks, the Atlas is also typically installed as a married transfer case using an Advance Adapters adapter housing. The adapter aligns the Atlas input with the transmission output shaft, and the case mounts in the stock transfer case location. Advance Adapters sells vehicle-specific adapter kits for the most popular 4x4 platforms, including the TJ, JK, JL, YJ, CJ, XJ Cherokee, ZJ, Ford Bronco, and Toyota Tacoma/Tundra/FJ Cruiser.
The divorced configuration is available for builds where a direct-bolt adapter does not exist for the specific engine/trans combination. In this setup, the Atlas hangs from the frame on a crossmember-type mount, connected to the transmission output by a short driveshaft. It requires three yokes (input, front output, and rear output) and is available in right or left drop configurations. This is a valid setup for certain custom builds, but it is not what we run in our race cars.
We manufacture our own Atlas transfer case mounts ($175.00) specifically designed for Bomber Chassis applications. These mounts are CNC-machined, bolt directly to the chassis rail, and position the Atlas at the correct height and angle for our leading arm suspension geometry. If you are running a Bomber Race Chassis or Bomber Trail Chassis, our mounts are a direct bolt-on.
Bomber Fab Atlas Transfer Case Mounts - $175.00 |
Bomber Race Chassis with married Atlas mounting provisions |
For custom applications, the Atlas can be adapted to virtually any transmission. Advance Adapters offers adapter kits for GM, Ford, Dodge, Jeep, and Toyota transmissions. Common pairings we see in the shop include the 4L80E (the most popular automatic for high-horsepower off-road builds), TH400, and various manual transmissions. If you are running an LS swap, check out our LS alternator brackets and LS motor mount kits to round out the drivetrain.
Building the Complete Drivetrain Around Your Atlas
A transfer case does not exist in isolation. It is one link in a chain that runs from the engine to the tires. Here is how we spec a complete drivetrain in a typical Bomber Fabrication race build:
Transmission4L80E automatic with Art Carr/Winters shifter. Proven in hundreds of KOH cars. Handles 700+ HP with the right converter and valve body. |
Transfer CaseAtlas 2-speed race case with 300M output shafts. 2.0:1 low range for KOH. Married directly to the 4L80E. Mounted on Bomber Fab CNC mounts. |
AxlesFull Spidertrax axle assemblies with Spidertrax knuckles front and rear. 300M inner shafts. 4.56 gears. Everything is Spidertrax on our race cars. |
Round that out with Wilwood 6-piston calipers, leading arm suspension, King shocks, and a full ECU Master dash to monitor every vital in real time, and you have a race car capable of taking on Johnson Valley. Need to protect the bottom end? Our engine skid kit keeps your oil pan and transfer case off the rocks.
Atlas Transfer Case Maintenance
The Atlas is a low-maintenance component, but it is not zero-maintenance. Here is what we recommend based on years of running these cases in race and trail conditions:
Where to Buy an Atlas Transfer Case
Bomber Fabrication is an authorized Advance Adapters dealer. We carry both the fully built Atlas race case (from $4,225.96) and the Atlas standard duty transfer case. We typically keep both race and trail cases in stock with no lead time, so your build does not have to wait. We also stock Atlas transfer case mounts ($175.00) and can help you spec the right case for your build.
Browse our full transfer case collection or check out the rest of our Bomber Builder parts catalog to spec your complete build. If you are putting together a Bomber Race Chassis (from $6,999) or Trail Chassis ($5,999) build, we can walk you through every component from engine to wheels.
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