Installing Chevrolet and GM Engines into 1972-1975 Jeep CJ

Novak

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https://www.novak-adapt.com/knowledge/engines/swap-guides/chevy-buick-gm/cj5-72-75-swap.html

Overview

Swapping a GM powerplant into a ‘72–’75 CJ brings modern reliability, power, and serviceability. These Jeeps were a major step forward mechanically — longer front clip, improved drivetrain layout — and are excellent candidates for V6 or V8 conversions.

The guide covers:

Transmission and transfer case options
Engine placement and mounts
Cooling, exhaust, and fuel delivery
Electrical integration
Emissions, clutch, driveshafts, and more

Factory Setup

Factory Engines:

Factory Transmissions (1972–1975):

T14 3-speed
T15 3-speed
T18 4-speed

Transfer Case:
The Dana 20 is compact, strong, and ideal for use with GM conversions.

Transmission Options

Automatic Transmissions:

Manual Transmissions:

T15 – strong factory 3-speed; use #1415 kit
T14 – suitable for V6s and mild V8s
T18 – great all-around 4-speed option
SM420 – ultra-low geared, adaptable via #422 kit
SM465 – refined and durable, adaptable via #462 kit
AX15 – strong 5-speed with overdrive, adaptable via #GMAX series and #152 kit
NV3550 – adaptable via #GMAX and #152 kit

Engine Choices

Ideal GM engines for the 1972–1975 CJ:

Avoid going smaller than 3.8L or larger than 400 ci — the goal is balanced, usable power without overtaxing the chassis.

Fuel & Exhaust

Carbureted or EFI systems both work, but EFI offers better reliability and performance.
Use a high-pressure pump (~60 PSI) for multi-point injection.
For fuel tanks without baffles, add a mini-reservoir or switch to an injected-style tank.
Headers: choose tight-fit block-huggers.
O₂ sensor bungs are required for EFI engines.

Cooling

The factory radiator won’t handle a GM swap.
Use Novak’s conversion radiators — bolt-in aluminum units with proper GM outlet configuration.
Aluminum dissipates heat faster and fits the narrow CJ grille perfectly.

Electrical

GM systems are straightforward:

Keep the PCM and wiring harness intact from the donor.
Treat the engine as if it’s still in its original chassis.
The PCM requires only power, ground, and ignition input.
Use our pass-through sensor for accurate VSS readings at the Dana 20.

Mounts, Clutch & Rear Support

Use Novak engine mounts — strong, adjustable, and designed for clearance.
Rear support: #RMU polyurethane mount works with all Novak adapters.
For clutch actuation, use the #HCR hydraulic retrofit kit for GM bellhousings.

Additional Considerations

Axles: Factory Dana 44 and AMC 20 axles are strong enough for V8 power.
Steering: Use the GM pump native to your engine with the stock Jeep box.
Brakes: Factory brakes are typically adequate; upgrade only as needed.
Driveshafts: Expect minor length changes — let the drivetrain placement dictate driveshaft length, not the other way around.

Planning Tips

Maintain firewall, frame, and axle clearances when positioning the engine.
Electric fans and short water pumps help maximize space.
Leave room for distributor access and exhaust routing.
Avoid cutting the firewall — the factory indentation provides enough space.

Have You Done This Swap?

If you’ve done a GM swap in your early CJ5 or CJ6, share your build details — engine, transmission, transfer case, and photos. These older Jeeps make some of the best-performing and most character-filled conversions out there.