AEM Jeep TJ Brute Force Intake System

By Shawn Pagan

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Okay so if you clicked on page two you probably want to see some outstanding numbers showing this Jeep TJ pulling 210 horsepower since, after all, the factory claims 190 horses. With all these modifications this one should be better than that, right? Well, not exactly. The factory generally uses horsepower numbers generated at the crank, not the rear wheels, so in a four wheel drive, 190 horsepower at the crank will be reduced by the transmission, transfer case, u-joints and driveline lash, rear end lash, etc. This one also has well over 60,000 miles on it, many of which have not been delicate. Rockcrawler is supplying you with real world numbers. The decision about the relevance to your installation is up to you, our dear reader. The important fact should be the percentage of increase, not the baseline or the end result, specifically.

Anytime someone wants to know exactly what a performance modification has done to a vehicle, they have to do a baseline. A baseline is a set of numbers that correlate to the performance of a vehicle that you can then compare any changes made against in order to understand just what the changes have done. In some cases, specific functions can be dialed in from the results of both the baseline and any subsequent test. That is one way of using a dyno as a tuning tool. Well, I didn't need one for tuning but I wanted to find a shop that not only had a dyno but could help me analyze the results since I am not an expert on those things.

After asking around near where I live I was pointed toward PFI Performance near Fort Collins, CO. PFI specializes in building horsepower and dyno tuning of both foreign and domestic vehicles. In fact, while we were in their shop they had two Jeeps, a number of Hondas, Mitsubishis, Mazdas and even an early model Ford Pickup with a Mazda Rotary Motor. In addition, it also made us feel good to know we chose a shop that takes time out of their busy schedule to hold "Dyno Days" which support local charities.

After talking with the owner and his team we decided that we would do a baseline pull with the AEM system installed and then work back to original form. Along the way we would also do some intermediate pulls (for example with the throttle body spacer not installed) to see where things took us along the way.

AEM Jeep TJ Brute Force Intake System
The dyno computer looks at home right there in the shop bay, doesn't it?
AEM Jeep TJ Brute Force Intake System
Backed into the bay with the rear tires on the dyno's drums.
AEM Jeep TJ Brute Force Intake System
PFI checked and double checked the straps holding the jeep into place. In addition, they also use screens to protect the operators and other vehicles in the shop.
AEM Jeep TJ Brute Force Intake System
Standing 10 feet from a vehicle running at redline on a Dyno can be a little unnerving - even though it was my vehicle and I was taking pictures, the speed of the rear wheel was amazing.

Of course, the important tests are comparing the AEM Brute Force Intake system to the factory system.

AEM Jeep TJ Brute Force Intake System
AEM intake
AEM Jeep TJ Brute Force Intake System
Stock intake

The results of the dyno testing were consistent and reasonably remarkable from pass to pass. The Jeep 4.0L is not a powerhouse and this one connected on the dyno with the stock intake tube, factory replacement filter and a slightly modified throttle body (not throttle body spacer) was pulling a whopping 102 horsepower and 206 lb.-ft. of torque to the rear wheels. However, when tested with the AEM Brute Force Intake installed our tests were also very consistent and showed an improvement in horsepower from 102 to 111 and an increase in torque from 206 to 216 lb.-ft..

*Note: All dyno tests were performed on the same equipment on the same day. Temperatures ranged from 53.31 to 69.98 and humidity from 7 - 9%.

AEM Jeep TJ Brute Force Intake System
The blue line is the AEM Brute Force, the red line is the stock intake and filter.

Note that the spike toward the end of the graph is an anomaly created by the specific configuration of this vehicle (it was consistent from test to test). We left them on the graph to show actual return from the shop. According to PFI, anomalies like these are pretty standard and shouldn't taint the data in any manner.

The dyno results from PFI Performance show a consistent 4.5-5% increase across the entire power band. I would say that isn't bad for a couple hundred bucks and an 30 minute driveway installation.

To make a couple of final points, I originally installed a throttle body spacer on this Jeep as an experiment. It proved to be worthwhile in that I got a minor increase in fuel mileage, but better yet, by the seat of my pants, the throttle body spacer also removed a slow speed, stomp on the gas flat spot or hesitation that I had. When we tested the AEM Brute Force system with and without the AEM throttle body installed, the results were similar to my previous spacer and the stock intake. The flat spot came and went with the spacer. The dyno did not show any increase or decrease in performance with or without it installed but PFI also supported the seat of my pants and fuel mileage results based on their experience. For article completeness I have included a comparison of the spacer I was using to the AEM spacer below. AEM stated that they found no difference using a fluted spacer over a smooth one, and at this point I must concur with their findings.

AEM Jeep TJ Brute Force Intake System
Side view comparison of the AEM throttle body spacer to the one previously used.
AEM Jeep TJ Brute Force Intake System
View from the bottom of each spacer. Notice the smooth inside of the AEM spacer.
AEM Jeep TJ Brute Force Intake System
Old intake with screw-like fins to "swirl air"
AEM Jeep TJ Brute Force Intake System
AEM chose a smooth intake

In addition to the increased performance over the course of four months, I have increased fuel mileage from 13.2 to 14.1 miles per gallon. I don't know that I can attribute all of that to the AEM Brute Force system, however I have not made any other changes that should effect the mileage to the vehicle. The only downside (if you can call it that) is that the air intake sound is pretty loud but not enough for me to care about, although it can catch people standing next to the vehicle by surprise as they generally think something is leaking vacuum under the hood. And if the truth be told, the polished tube looks great under the hood.

In conclusion, I am very happy with the AEM Brute Force. It increased my pathetic horsepower and increased my fuel mileage all for a few hundred bucks. AEM provides a complete product with decent instructions. I didn't get to test out their customer service, which I do on many installations. The product worked as advertised. What else needs to be said?

AEM - Advance Engine Management, Inc.
2205 126th Street, Unit A
Hawthorne, CA 90250
(310) 484-2322
PFI Performance
5720 South Bueno Dr.
Fort Collins, CO 80525
(970) 377-2216


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Shawn Pagan

Shawn Pagan is a staff writer for as well as Our Land Use Editor. Shawn resides in northern Colorado.

Contact Shawn at

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