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.
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.
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.
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.
The dyno computer looks at home right there in the shop
bay, doesn't it?
Backed into the bay with the rear tires on the dyno's drums.
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.
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
the important tests are comparing the AEM Brute Force Intake system
to the factory system.
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..
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
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.
Side view comparison of the AEM throttle body spacer to
the one previously used.
View from the bottom of each spacer. Notice the smooth inside
of the AEM spacer.
Old intake with screw-like fins to "swirl air"
AEM chose a smooth intake
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.
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