Official Novak Reference Thread!!!
This post serves as the master swap guide for installing Chevrolet and GM engines into Jeep XJ Cherokees, Wagoneers, and MJ Comanches.
You’re welcome to ask questions, share photos of your builds, or post tips and corrections below.
First, our detailed XJ conversion instruction package:
📄 Read Novak’s detailed XJ/MJ conversion instruction package (PDF)
🏁 Overview
One of the most fascinating powertrain conversion platforms among the Jeeps are those into the Jeep XJ Cherokee. These were a little daunting in the early 2000s due to fitting mounts and the engine into the narrow, compound-bent unibody frame. XJ conversions are now among the most well-paved and successful of conversions.
With improvements in power, fuel economy, reliability, and drivability, there is nothing like an XJ with a GM V8.
🕰️ A Little History
The XJ Cherokee was a significant departure from earlier Jeeps, being the first with unitized body construction, coil spring and track arm front suspension, and excellent road manners. It was produced from 1984 to 2001 in three major stages:
- Stage I: 1984–1986
- Stage II: 1987–1996
- Stage III: 1997–2001
The XJ’s lightweight and durable chassis make it an excellent swap platform for GM power.
⚙️ Factory Engines
- AMC 2.5L I4 (105 hp) — Carbureted, later MPI version improved slightly
- Chevrolet 2.8L V6 (115 hp) — Weak, common reason for swaps
- AMC 4.0L I6 — Released in 1987, improved in 1991 with Mopar Fuel Injection (190 hp)
Why swap? The 4.0L I6 is reliable but heavy and thirsty; GM power adds efficiency and modern drivability.
🧱 Factory Transmissions
- AX4 / AX5 — Light-duty, unsuitable for swaps
- Peugeot BA10/5 — Weak, failure-prone
- AX15 — Strong and adaptable, great for GM engines
- AW4 — Durable but limited by computer controls
✅ The AX15 is the only factory transmission worth keeping. It adapts well to GM engines with Novak’s GMAX adapter kits.
🔩 Transfer Cases
- NP207 — Early, okay for mild power
- NP231 — Excellent, part-time 4WD
- NP242 — Part/full-time, slightly weaker but usable
Both NP231 and NP242 adapt easily to GM automatics and manuals.
🔧 Transmission Options
Automatic Transmissions
Manual Transmissions
🔩 Engine Options
Because of the XJ’s low hood, use low-profile LS or Small Block setups — avoid tall intakes or truck accessories.
💨 Fuel Injection vs. Carburetion
Fuel injection offers superior efficiency, drivability, and reliability. Carburetors may seem simpler but lose performance and emissions compliance.
🌎 Emissions
See Novak’s emissions article. Follow the same-year-or-newer rule and retain emissions equipment.
🧰 What to Pull From a Donor
- Engine (with accessories and brackets)
- PCM / ECM and wiring harness
- Matching transmission
- Power distribution center (relay/fuse block)
🧱 Engine Mounts
Use Novak’s XJ Engine Mounts — precision-engineered for correct placement of Gen I–III GM engines.
❄️ Cooling
Use Novak’s XJ Cooling System Components for bolt-in aluminum radiators that eliminate the remote pressure bottle.
⚡ Electrical
GM PCM systems are reliable and self-contained. Use the Crank Position Emulator to integrate factory XJ gauges.
🧮 Gauges, Steering & Suspension
- Retain factory power steering gear; adapt lines as needed.
- 2–3" lift helps with clearance, but not required.
- Use I6-rated springs for V8 swaps.
⛽ Fuel System
🔥 Exhaust
🔩 Driveshafts & Crossmember
🦴 Axles & Linkages
🛞 Brakes
- If they were good before, they’ll be good after.
- Upgrade only for extreme use or larger tires.
🧭 Summary
No change you can make to an XJ or MJ is more rewarding than a proper GM powertrain conversion. The combination of modern GM power and Jeep capability transforms drivability while keeping the Jeep spirit intact.
Each swap is unique — but with solid planning, the right Novak components, and this guide, your conversion will be straightforward, reliable, and a blast to drive.
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Have you done this swap in your XJ or MJ?
Share your setup, transmission choice, and lessons learned below! 👇
