Official Novak Reference Thread!!!
This post serves as the master swap guide for installing Chevrolet and GM engines into Full Size Jeeps (FSJ), Trucks, Wagoneers & Cherokees.
You’re welcome to ask questions, share photos of your builds, or post tips and corrections below.
📄 Read Novak’s detailed FSJ conversion instruction package (PDF)
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The Full Size Jeeps (FSJ’s) — including the Wagoneers, J-Trucks, and Cherokees — are among the most noble and impressive Jeep vehicles ever made. They’ve become some of the most sought-after and treasured Jeeps for restorations and swaps alike.
The FSJ is one of the simplest and most accommodating Jeep platforms for a powertrain conversion. The Wagoneers and J-Trucks changed very little from 1962–1991, making them extremely consistent to work with.
We recommend the following engines as top choices:
GM engine conversions into these Jeeps are exciting, beneficial, and well-documented. Moving to a cleaner, stronger, reliable, and serviceable GM powerplant is one of the best improvements you can make.
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Factory Engines
Factory Transmissions
The FSJ lineup featured a wide variety of transmissions, including:
- T90J — three-speed, common behind I6
- T98 — optional four-speed through 1966
- T14 — behind the Buick 225
- T15 — three-speed, strong and durable
- T18 — four-speed, used 1966–1987
- TH400 — behind the Buick 350 & AMC V8s (1967–1979)
- TF727 — with AMC V8 (1980–1991)
- T176 / T177 / T178 — four-speed, AMC I6 (1980–1987)
Transfer Cases
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Planning the Powertrain Conversion
Transmission Choice
It’s crucial to plan around the transmission early — it can dictate your adapter, driveshafts, and engine placement.
You can use Novak’s gearing calculator to find your optimal combination.
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GM Automatic Transmission Options
- TH350 — strong, compact, reliable. Adapt to Dana 20 with #103 kit or FSJ NP cases with #135 kit.
- TH400 — heavy-duty, ideal for towing or big builds. Adapt to Dana 20 or FSJ NP cases with #124 kit.
- 700R4 — overdrive and great ratios. Adapt to Dana 20 with #172 kit or FSJ NP cases with #137 kit.
- 4L60E — ideal for Gen III+ engines. Adapt to Dana 20 with #4L62 kit or FSJ NP cases with #137G kit.
✅ FSJ chassis length means you rarely need to shorten driveshafts — an advantage for these conversions.
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Manual Transmission Options
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Transfer Case Choice
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Engine Choice
Our top choices:
✅ FSJ engine bays are extremely forgiving — even big blocks fit easily. Most installs offset 1"–1¼" toward the passenger side for steering clearance.
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Injected vs. Carbureted
Fuel injection wins every time for drivability, efficiency, and reliability. Modern GM injection is far simpler than most people assume.
Avoid carb-swapping a Vortec or LS engine — it adds cost, complexity, and reduces performance.
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Emissions
Most FSJs fall outside of modern emissions testing, but if applicable, follow your state’s requirements.
Your Jeep is considered a “Light Truck,” meaning engines from GM trucks, SUVs, or cars generally qualify.
More details: Emissions Overview
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Cooling
Use Novak’s FSJ KryoFlow radiator — designed for GM outlet positions and efficient heat dissipation.
For Gladiator-style FSJs, Novak can assist with custom-fit radiators.
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Electrical
Modern GM PCM systems are simple and reliable. The key principle:
“Make the engine think it’s still in its original GM chassis.”
For gauge integration, use Novak’s #2PRS VSS sensor to retain speedometer and ECM input.
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Steering & Suspension
All factory steering components are retained. FSJs handle V8 weight with ease, and often don’t require any suspension lift for engine swaps.
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Fuel Delivery
For fuel-injected engines, ensure a steady, high-pressure supply. Use in-tank or external EFI pumps and consider Novak’s fuel system components.
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Exhaust
Tight-fit, block-hugger headers work best. Maintain heat shielding and proper O₂ sensor placement. 2½" exhaust is ideal.
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Crossmember & Rear Mount
Use the Novak #RMU rear mount — strong, simple, and fits most FSJ configurations.
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Brakes
- If they were good before, they’ll be good after.
- Upgrade only for extreme builds or larger tires.
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Summary
No change you can make to an FSJ is more rewarding than a proper GM powertrain conversion.
With modern power and proven Jeep capability, the FSJ becomes a truly unique, powerful, and reliable classic.
Each swap is unique — but with solid planning, the right Novak components, and the right guidance, your FSJ conversion will be straightforward and built to last.
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Have you done a GM swap in your FSJ, Wagoneer, or J-Truck?
Share your setup, transmission choice, and lessons learned below! 👇
