What To Expect From Common Bolt-On Jeep Power Adders

    How To Make Horsepower

    One of the more commonly asked questions we get from most Jeep owners is: “How can I make more power?” It seems like a simple enough question, however with so many different Jeep engines used over the years, there is no one silver bullet. Also, what one person considers a power increase may be a waste of time and money to another person. An interesting thing we’ve noticed is that it’s very common for speed-part companies to be confused about the power needs of the typical Jeep enthusiast. The companies often try to focus on power and torque in increasing off-road performance, where in reality, that’s where low gearing is generally more important. Increased horsepower off-road isn’t needed unless you frequent mud, sand, and steep, slick climbs. Most of us want engine mods to help maintain highway speed on the road, get up a steep grade, or pass an 18-wheeler with at least a little bit of dignity and respect. For over a decade and a half, we’ve driven on, tested, and dyno’d more than enough parts to fill an entire Jeep speed shop. Aside from adding a turbo or supercharger, combining any number of these bolt-on performance parts will typically result in about a 20hp increase. And while 20 hp will be noticeable from behind the wheel, the dollar per horsepower ratio can be unusually high. For that reason, we recommend you consider the other benefits of the many bolt-on power parts available. We have compiled information about some of the most common Jeep engine modifications. You’ll be able to identify the right power adder, or combination of power adders that will work for you and your Jeep.

    Cold Air Intake
    Dollar for dollar, there is no better modification you can make to your Jeep to increase power output. Test after test that we have done has proved that no matter what Jeep engine you have, an aftermarket cold air intake will make more power than stock, and in many cases, even increase fuel economy. Why is that? Well, the OE manufacturer has other things to consider that the aftermarket companies generally do not, such as noise and water resistance. Sealed air boxes and baffled intake tubes make less noise and keep water out, but they also impede airflow. Most aftermarket cold air intakes will make your Jeep slightly louder than stock, partly because of the freer-flowing open element. And even if they have some sort of shielding around the filter, they generally are not as deep-water friendly as the stock air box found on most newer Jeeps. Also, look for filters made with synthetic media. The synthetic filter media traps the dirt particles far better than oiled cotton filter elements.
    Additional Power: 5-10 hp
    Pro: Dollar for dollar, the best power mod you can make
    Con: Increased noise and most kits make your engine less water resistant

    Throttle Body or Carb Spacer
    Ever heard the term “snake oil”? It could just as easily be replaced with “throttle body spacer.” Of course, you will see some gains with a spacer on a carbureted or throttle body engine with a wet manifold. However, all Jeeps since about 1991 have modern multi-point injected engines where the spacer is insignificant. Of all the MPI engines we have tried spacers on, none of them have made more power on a dyno. Is it possible that the spacer does make more power in some narrow unmeasurable rpm range? We suppose so, but if it’s only making more power under specific conditions that rarely occur, why waste your money?
    Additional Power: 0-2 hp for MPI and 5-8 hp for carb spacer
    Pro: Colorful anodized aluminum looks cool under the hood
    Con: Basically a waste of money on any multi-point fuel-injected engine

    Electronic Tuner
    Jeep spends years and millions of dollars developing engine management systems designed to provide the most reliable power output while still maintaining fuel economy. Most electronic tuners or “chips” have far less research and development done on them. Aside from the diesel market, it’s been our experience that many aftermarket gas tuners do more harm than good. They often trigger check engine lights or cause the vehicle to go into limp mode, depending on the application. But, many of these electronic tuners have other useful features, such as the ability to reprogram the electronic speedometer for tire size and axle gearing alterations. This feature alone is worth the purchase price because it will correct automatic transmission shift points, and ultimately improve performance both on- and off-road. Another feature many of these controllers have is the ability to change the parameters for the tire pressure monitoring system. Larger aftermarket tires generally don’t require the same pressures as the small stock tires, so this feature eliminates the annoying TPMS light on the dash and the incessant chime warning on ’07 and newer Jeeps. Other functional features are also common and some controllers are designed to simply give you access to these features and don’t mess with the engine management at all.
    Additional Power: 0-17 hp
    Pro: Most electronic tuners offer off-road worthy features
    Con: As for making more power, they frequently cause more pain than glory

    In the past, restrictive cast iron manifolds robbed power from some engines. Today, as mentioned earlier, the OEs, including Jeep, spend millions of dollars developing modern powertrains. If there are any fuel or power efficiencies to be had, you can bet the company has looked into it. Older Jeep engines will see more power gains from the addition of a quality set of headers. On modern Jeeps, it’s been our experience that it’s best to simply buy headers to replace cast-iron exhaust manifolds that are known to crack, such as the exhaust manifolds found on the Jeep inline-sixes. When choosing a header, look for thick, high-quality materials like stainless steel. If you can’t swing the coin needed for thick-tubed stainless steel headers, look for steel headers with the thickest tubes and flanges that you can find. These will last longer, especially if they have a special heat-resistant coating to keep them from corroding.
    Additional Power: 5-10 hp
    Pro: A great alternative for stock cast manifolds that are known to crack
    Con: All by themselves, a negligible increase in power without other modifications on modern engines

    Cat-back Exhaust
    If it’s loud, it must be making more power right? Not always. In some cases, we have seen a loss of power on the dyno with the installation of an cat-back exhaust kit. Ultimately, if you like your Jeep loud, find an exhaust kit that has a tone you like. The power gains will be negligible in most cases. If you live in the rustbelt, you can upgrade to a system that is 100 percent stainless steel for longer life.
    Additional Power: 0-10 hp
    Pro: Makes your Jeep sound cooler than stock
    Con: Makes your Jeep louder

    Larger Throttle Body
    All by itself, a larger throttle body does little to increase the power under the hood of your Jeep. But when you combine a larger throttle body with a turbo or supercharger, intake, exhaust and so on, now you really have something. We would generally steer away from a larger throttle body unless some sort of forced induction is planned and you are looking to reap the maximum benefits.
    Additional Power: 0-5 hp
    Pro: Lets more air in, great for turbos and superchargers
    Con: Negligible power increase on a stock motor

    Bigger Fuel Injectors
    Similar to the addition of a larger throttle body, you really don’t need larger injectors on a mostly stock engine. The benefits will be hard to justify given the purchase price and loss of fuel economy. New larger injectors are typically supplied with turbo and supercharger kits, so if you ultimately plan to add forced induction, hold off on purchasing the injectors separately; it will save you money in the long run.
    Additional Power: 0-5 hp
    Pro: Unneeded on stock motor, necessary addition for most turbo and supercharger kits
    Con: Decreased fuel economy and no significant power increase on stock engine

    Older Jeep engines such as the AMC V-8 and carbureted inline-sixes can benefit greatly from the addition of a more modern and reliable ignition system with a hotter spark. These engines are notorious for having weak and unreliable ignitions. The hotter, more precise spark will make the engine burn cleaner and more efficient, ultimately making the Jeep more drivable on- and off-road. Newer fuel-injected Jeep engines will see far less return with the addition of a high-performance aftermarket ignition.
    Additional Power: 0-10 hp
    Pro: Some older engines will benefit greatly
    Con: Newer engines will see less return

    Of all the bolt-on power adders available, the addition of a supercharger kit is the closest you will get to match the performance of a swapped-in engine. From behind the wheel, a four-cylinder will feel like a six-cylinder and a six-cylinder will feel like a small V-8. However, like an engine swap, or any power adder for that matter, a supercharger does have some drawbacks. Supercharger kits generally cost more than $5,000 and require a labor-intensive installation by an experienced mechanic. Many people incorrectly believe that a supercharger will provide better fuel economy. It’s been our experience that they do not. We saw a significant loss of fuel economy on a Jeep 4.0L inline-six and on a 3.8L V-6. Also, most supercharger kits will require the engine to run on premium fuel, which is an additional cost to consider. Engine life will typically be shorter than on the same engine without a supercharger, and the supercharger itself will likely need rebuilding every 100,000 miles or so.
    Additional Power: 60-100 hp
    Pro: Very noticeable increase in power
    Con: Can be complex, expensive, and unreliable

    A turbo kit has many of the same power output advantages of a supercharger, as well as the high cost, reduced fuel economy, and less-than-OE reliability. A turbo can also make underhood heat management a little more difficult. To combat this, some turbo kits mount the turbo far downstream of the engine and under the chassis. However, we think the turbo lifespan in this location would be very limited, especially if it is frequently quenched during deep water crossings or when it builds up excessive heat after being caked with mud.
    Additional Power: 60-100 hp
    Pro: Very noticeable increase in power
    Con: Can be complex, expensive, and unreliable

    Larger diameter tires move your Jeep’s engine rpm lower and out of the sweet spot where it makes the most efficient power for a given road speed. Hands down, the biggest increase in performance and drivability on- and off-road will come from a gear swap that matches the bigger tires on your Jeep. Technically, a gear swap does nothing to increase your engines output, but it significantly improves how your Jeep will put power to the ground. Deeper gears can also be used to help push the added weight of a fullsize spare tire, off-road worthy bumpers, body armor, a winch, and so on. If you have a modern Jeep with an overdrive gear and 33-inch tires, you should be running at least 4.10 gears, with 35s at least 4.56 gears, and with 37s at least 5.13 gears. Older Jeeps without an overdrive transmission will typically benefit from slightly less gearing. How deep you go with your gear swap will depend on the engine and transmission in your Jeep, overall weight of the vehicle, and your driving habits.
    Additional Power: 0 hp
    Pro: Most cost-effective and reliable increase in performance and perceived power
    Con: More expensive and more difficult to install than simple engine bolt-ons

    What Comes In, Must Go Out
    When deciding to purchase performance parts for your Jeep engine, think of it as an air pump. It sucks air in the intake and blows it out the exhaust. If one side of the pump is restricted, you’ll be limiting your horsepower potential. Say, for example, you install a supercharger on your engine. You can bet that the stock exhaust and air box isn’t up to the task of the increased airflow. So if you make a modification like this, you’d also want to consider an free-flowing air filter assembly, headers, a high-flow catalytic converter, and a cat-back exhaust, at least if you want to reap the full benefits of the supercharger.

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