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How to Upgrade Jeep 258 Engine? (Cost, Explained)

Since the beginning, owners have had the temptation of replacing the 4.2L Jeep 258 engine with a bigger Chevy.

But that can’t do any good because 258 is a solid engine with impressive and reliable performance.

However, there is room for improvement. In this article, I am going to tell you how to upgrade Jeep 258 engine properly at a minimal cost.

Can You Upgrade Jeep 258 Engine?

Yes, you can upgrade your Jeep 258 engine to increase mileage, fuel efficiency, horsepower, and torque.

Replacing the whole engine with another one is not a good idea for this particular case. Hence, I have suggested some part upgrades below.

Before you start reading that, it would be better to know the right time for investing so much money in your car.

When Should You Upgrade Jeep 258 Engine?

We know that Jeep AMC 258 engines are in the older Jeep models. And, you can understand that older engines can’t perform like new for various reasons.

The parts wear off, lose efficiency, and can’t ensure the original spec.

Another thing is that some stock parts are not very good at unleashing the full power of an engine. And, it is true for the 258 too.

Manufacturers intentionally do that to ensure reliable performance rather than showing maximum power of an engine.

No matter what the reason is, you have to realize whether it is a necessity or not. Also, it requires a couple of thousand dollars to do it.

Read the full article, think it through, and decide which would be better for your Jeep. It can be a full upgrade or a partial one.  

How Much Does It Cost to Upgrade Jeep 258 Engine?

There are two cost parts in this whole engine upgrade scenario. One is the labor cost and the other is the product cost.

Among the two, I can’t predict how much your local car mechanic is going to charge.

On the other hand, I can give you the estimated cost on the product side.

Considering you are only buying a fuel injector (not the whole fuel injection system), you may have to spend slightly over 1000 dollars.

Also, the mechanic can suggest some parts to be replaced which will increase the overall cost. Within $2000, everything should be done.

My Top Recommendation on Jeep 258 Engine Upgrade:

I have gathered the upgrade recommendations from different forums. Users who have already done it suggested the best aftermarket brand in those threads.

Also, I crosschecked the suggestions to make sure that they can outperform the stock ones.

1. Flowmaster 942551 50 Series Df Muffler

In order to increase horsepower, torque, and engine efficiency, one can upgrade their stock muffler by installing this one. It is made from alloy steel to ensure maximum durability and smooth performance.

2. Air Intake Manifold 4.2L

Installing this performance air intake manifold, you can successfully increase the horsepower and RPM range of your Jeep 258 engine. It can feed more air and fuel to the engine for better output.

3. NGK G-Power Platinum Spark Plug

I like it because of its trivalent metal plating which fights against corrosion. Moreover, the copper core is very efficient at reducing heat. Installing this spark plug, you can increase fuel economy, get a better starting, and enjoy superior acceleration.

4. COMP Cams K68-232-4 Xtreme

The cam kit includes everything to upgrade the camshaft along with the supporting parts. The price is a bit higher, but you won’t have to spend time trying to find the right components separately. It improves engine performance by increasing valve-opening timing and duration.

5. Fuel Injection Kit

So far, I have only found a full fuel injection system for old Jeeps with AMC 258 engines. These are costly. However, you can also replace only the fuel injector which costs around $50. It would be better to talk with a local Jeep dealer or car shop to find the right part.

6. 3571-JL Superchips Flashcal

Here, I have found a popular handheld programmer for your Jeep 258 engine. It can let you access the car’s ECU easily, and tune for increasing the performance.

How to Upgrade Jeep 258 Engine?

There are lots of different parts of an engine that needs to be upgraded. I have already listed the products above.

Now, I am going to explain the procedure for replacing the stock parts with the better aftermarket ones.  

Unfortunately, I can’t explain every upgrade detail in this small article. All I can do is give you an overview, and share videos of the procedure.

1. Upgrading Performance Exhaust

A Jeep Wrangler owner did the upgrade and recorded everything so that others can do it too. Watch the video by clicking here.

No matter what Jeep series you own, as long as it has a 4.2L 258 engine, you can replace the stock exhaust with a Flowmaster 40 or 50 series.

Those who don’t have any experience with the engine should leave the task to a mechanic. and

2. Upgrading Cold Air Intake

When it comes to the bigger engine parts such as intake and exhaust manifold, it is better to hire a mechanic.

As several small but significant attention-to-detail steps are involved, most DIYers can’t do it right.

Still, I am sharing a video of installing a new cold air intake manifold in the Jeep 258 engine.

Those who already have some experience with complex engine repairing tasks can try it.

3. Upgrading Spark Plugs

I have already suggested the spark plugs above. But you will also need A-Team Performance Wires for optimum and reliable performance.

Together, they can ensure more fuel combustion resulting in increased engine performance.

Replacing the above parts require a certain level of expertise. But that is not the case for spark plugs. Watching this video, one can easily do it in their garage.

4. Upgrading Camshaft

After going through several forums, and reading through expert comments on this topic, I found that upgrading a camshaft is better off with a mechanic.

I couldn’t find any suitable video showing the replacement procedure for the Jeep 258 engine.

5. Upgrading Fuel Injectors

While you upgrade the fuel injectors, it will be better to replace the fuel filters too.

This combination can improve engine fuel economy by removing impurities. Also, your Jeep will vibrate not as much as before which makes acceleration smoother.

A variety of tools are required to do the replacement. Here is a video showing the proper and easiest way to do it.

You can find the tools and upgrade parts on Amazon. I have already suggested high-performance fuel injectors in the recommendation section above.

6. Installing Turbochargers

Deciding between superchargers and turbochargers can be difficult as both are helpful for increasing the horsepower of a car engine.

But turbochargers are superior, and I recommend you install one in your Jeep AMC 258 engine.

But installing one to upgrade the engine is a daunting task and requires lots of repairing skills. It is better to talk to a mechanic about the installation.

You should know that there are no direct turbochargers for Jeep 258 engines. However, any kit compatible with Jeep 4.2L engines can fit perfectly.

7. Using Performance Tuning

After installing a few upgraded aftermarket parts, you will have to tune the engine for better mileage and fuel efficiency.

I have seen that experts use Superchips F5 tuner to achieve the expected performance.

Here is an official video showing how to initiate the process in the right way.


That is all describing how to upgrade Jeep 258 engine. Do some research on this famous Jeep engine, and you will know why I want you to keep it.

Replacing the whole engine can give you more horsepower or torque, but you won’t ever get the same performance or reliability. So, I highly recommend you upgrade the mentioned parts in the Jeep 258 engine and enjoy the thrill of off-roading.

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