What Is The Best Jeep 40 Head

Jeep engines have a long history of power, durability, and off-road performance. For many Jeep owners and mechanics, the 4.

0-liter inline-six engine is legendary. But a key factor in this engine’s reliability and power is the cylinder head, often called the “40 head.”

Choosing the best Jeep 40 head can be confusing because there are so many versions and casting numbers. This guide gives clear answers by breaking down the 40 most common Jeep 4.

0 heads, what makes them unique, and which one might be best for your needs.

What Makes A Jeep 40 Head Special?

The Jeep 4.0 head is a vital engine part that covers the cylinders, forms the combustion chamber, and holds the valves. Over the years, Jeep used many head designs. Each version impacts performance, reliability, and compatibility. Some heads crack easily, while others offer more power or better cooling.

The 40 Best Jeep 40 Heads Explained

Below you’ll find a brief overview of 40 popular Jeep 4. 0 heads.

Each one has its own story and ideal use.

• 2686 – Early AMC design, solid but rare. Good for original restoration.
• 2687 – Similar to 2686; slight cooling improvements.
• 2688 – Used in early XJ Cherokees; reliable but hard to find.
• 2689 – Improved casting; better flow, but not common.
• 7120 – Found on 1991–1995 4.0s. Known for excellent airflow. A favorite for mild performance builds.
• 0630 – 1996–1999 head. Good mix of strength and flow. No major cracking problems.
• 0331 – 2000–2001 head. Prone to cracking, especially between cylinder 3 and 4. Avoid if possible.
• TUPY 0331 – Late 2001 replacement for 0331. “TUPY” cast in head. Much stronger, fixes cracking issue.
• 479 – Used in late ‘80s. Not common, but durable.
• 3721 – Early casting, suitable for stock rebuilds.
• 3258 – Similar to 3721. Low performance, but reliable.
• 3246 – Found in some export models. Decent for daily driving.
• 7123 – Special XJ head; moderate performance.
• 3251 – Basic casting; not favored for upgrades.
• 0635 – Improved coolant passages; rare.
• 6758 – Performance-oriented; larger valves.
• 730 – Used in military Jeeps; extra strong.
• 6765 – Good for high-mileage engines.
• 3713 – Seen in Comanche trucks; dependable.
• 7121 – Close to 7120 in quality.
• 3712 – Early ‘90s casting; average flow.
• 7122 – Slight changes over 7121; similar strength.
• 0632 – Good for mild upgrades.
• 3253 – Reliable, but not high-flow.
• 0631 – Used in Wranglers; solid, but not the best for racing.
• 7125 – Rare, but strong.
• 0633 – Improved over 0631; better for cooling.
• 3259 – Notable for durability in hot climates.
• 3714 – Average; found in fleet vehicles.
• 0634 – Minor updates, mostly stock use.
• 3255 – Good if you want an affordable rebuild.
• 3256 – Slightly lighter casting.
• 3715 – Used on export models.
• 3716 – Similar to 3715, but with improved flow.
• 3717 – Good for low-emission builds.
• 3718 – Used in some Grand Cherokees.
• 3257 – Late ‘90s; dependable.
• 7126 – Not common, but offers steady performance.
• 0636 – Latest production head before switch to newer engines.
• TUPY 0630 – Rare, but combines TUPY strength with 0630 flow.

How Jeep 40 Heads Compare

Choosing the best head depends on your goal: power, reliability, or daily driving. Here’s a quick comparison:

Which Jeep 40 Head Is Best For You?

If you want maximum power for racing or off-roading, the 7120 head is often the top choice. It offers the best airflow and is easy to modify. For daily driving or a mild rebuild, 0630 is a safe bet—strong, reliable, and widely available.

If you own a 2000–2001 Jeep, check your head for “TUPY” marking. The regular 0331 cracks, but TUPY 0331 is much better. For pure durability in extreme conditions, the TUPY 0630 (if you can find one) is excellent.

Common Mistakes When Choosing A Jeep 40 Head

• Picking a 0331 head without checking for cracks. Always inspect used heads carefully.
• Ignoring casting numbers. Small differences can cause big problems with fit and reliability.
• Overlooking TUPY heads. These are much stronger and last longer.

Quick Reference For Jeep 4.0 Head Features

Non-obvious Insights About Jeep 40 Heads

• Some heads have minor differences in coolant flow. This can lead to overheating if you swap heads between years without checking water jacket holes.
• The TUPY heads not only resist cracking but often outlast the rest of the engine—making them a smart long-term investment even if they cost more upfront.

Final Thoughts

Choosing the best Jeep 40 head is about knowing your engine’s needs and understanding the differences between casting numbers. The 7120 head is best for performance, 0630 for daily reliability, and TUPY 0331 for modern Jeeps needing strength. Always check casting numbers, watch for cracks, and don’t cut corners—your Jeep’s power and life depend on this part. For more technical details, you can explore the AMC straight-6 engine page.

Frequently Asked Questions

What Is The Most Reliable Jeep 4.0 Head?

The TUPY 0331 head is the most reliable for 2000–2001 models because it fixes the common cracking problem.

Which Head Gives The Most Horsepower?

The 7120 head is best for horsepower due to its superior airflow and ease of modification.

How Can I Tell If I Have A Tupy Head?

Look for the word TUPY cast into the head, usually near the valve cover. This marking confirms the upgraded design.

Is It Worth Upgrading From 0331 To 7120?

Yes, if you want more power and reliability, upgrading to a 7120 head is a smart move. It requires some changes to fit, but the benefits are strong.

Can I Use Any Jeep 4.0 Head On My Engine?

Not always. Small differences in coolant passages and sensors mean you must match the head to your engine’s year and model for best results.