this point, we were ready to roll. The computer was started and
the Jeep was put through it's paces, accelerating up through the
gears until the rpms hit the redline and the brakes were hit to
slow the wheels to a stop. If you've never been in a tight enclosed
space next to a vehicle running over 5000 rpm in front of you, you
have no idea how scary it can actually be. The noise is nearly deafening
and the spinning of the wheels causes your heart to race as the
Jeep tries its hardest to break free of the straps.
Parked on the dyno dru, ready to go.
This is not the safest-feeling place to be standing!
lasted about a minute and then we went into the office to check
out the graphs on the computer. We did this three times and decided
on the "baseline" pull. We tossed out anything weird-looking
and took the average pull, where we recorded a maximum of 151.56
horsepower at around 4,550 rpm. Stock specs for our Jeep from
the factory are 190hp at 4,600 rpm.
A monitor simulates speedo and RPM guages.
Inside the office, we could check out the results.
Now you might
wonder why there is such a big difference between the stock and
the baseline figures. The reason is that the factory figures are
at the flywheel, not at the wheels. Power and torque are lost
as it travels through the driveline of your vehicle before finally
ending up on the ground. To compensate for this loss, a typical
conversion is to add 20% to a dyno pull to get a comparable number.
Using this, we would take 151.56/.80 = 189.45hp, which is only
about a half of a horse below Jeep's figures. This seemed about
As for torque, our baseline pull showed 193.23
ft.-lbs. at about 3,750 rpm, whereas the stock specs claim 225
ft.-lbs. at 3,000 rpm. Adding 20% to our figures gives us 241.54
So now it
was time to add the Dynomax into our equation. We went next door,
but after an hour of fiddling, banging, prying, and downright
crying, we just couldn't bust the old muffler away from the catalytic
converter. The clamp from the factory had pinched the tubing too
tightly and we weren't getting it off without a torch - which
we didn't have. Mission aborted.
to take the Jeep to a muffler shop and have them swap the exhaust
for us. Knowing everything would fit perfectly onto the stock
exhaust hangers (it did), all they'd have to do is free the old
exhaust and clamp on the new one. The Jeep was finished that morning
and we were ready for another dyno visit. The only hitch was that
the muffler shop said our cat was pinched too tightly by the original
clamps and they decided to weld the Dynomax on to avoid any exhaust
leaks. Cost was one hour of labor, which was about $45.
Dynomax installed. Notice weld at the cat.
The Dynomax exists in the stock location.
The weather was almost identical that night and
we headed back to Walker Dynotune at roughly the same time of
day, hoping for consistent atmospheric conditions.
time, for fun, we also added Davis Instruments' new CarChip
E/X OBD II scan tool to our arsenal. The CarChip
is a small module that plugs right into your OBD II connector
under your dash. It then records everything that goes on in your
vehicle's computer for up to 300 hours of drive-time, from rpm,
throttle position, coolant temperature, manifold pressure, O2
sensor voltage, fuel pressure, timing advance, and more. You can
then easily download the information and view it later on your
home computer. We have included the results from the CarChip
here for you to view.
the Jeep right up, did three more pulls and checked out our results.
Our third pull scored 157.28 hp at roughly 4,600 rpm and 200.33
ft.-lbs. of torque, peaking around 3,600. Adjusted figures would
then be 196.6 hp and 250.41 ft. -lbs. Using our actual figures,
the Dynomax gave us a gain of 5.72 hp and 7.1 ft. -lbs. of torque,
netting us about a 4% gain. It's interesting to note that on some
pulls we gained more and some less. We had one pull that showed
as much as an 8 horsepower gain. But we threw it out and took
the average pull. We also tossed out an initial torque bump on
the baseline pull's torque curve.
Walker Dynotune can send you home
with a CD to use at home for viewing your Dynojet results.
Click on the charts below to see larger versions.
Horsepower/RPM - Red=baseline Blue=Dynomax
Torque/RPM - Red=baseline Blue=Dynomax
We asked Dynomax
what to expect and they told us that they typically record a 10%
gain in both horsepower and torque on 6-cylinder vehicles. They
also said that they had not actually tested this system on a dyno,
though, so they had no figures to compare to.
||190 HP @ 4600RPM
||225 ft. -lbs. @ 3000RPM
||189.45 HP @ 4550RPM
||241.54 ft. -lbs. @ 3750RPM
||196.6 HP@ 4600RPM
||250.41 ft. -lbs. @ 3600RPM
||* Baseline & Dynomax show 20%-adjusted figures
So there are
the scientific numbers. But how does the Dynomax sound and how
does it feel to drive the Cherokee now?
Click to see and hear a Windows Media movie of the Jeep
with the Dynomax installed.
The sound is exactly what we were looking for.
It's got a good throaty tone and sounds like it means business
when you really romp on the pedal. But, when you are driving "normally"
the exhaust just sounds nice and is not overbearing. Even at full-tilt,
you can still have a conversation inside the Jeep and it does
not cover up the radio.
But the big
question of how it performs has been answered. The Dynomax truly
made a huge difference in how the Jeep behaves on the street.
Gone are the knocks when we go up the hills. In addition, the
Jeep just feels better. It wants to go now. If you told me that
we'd get six horsepower difference and that I could actually feel
it, I might have shrugged my shoulders and said, sure thing...whatever.
But the truth is, we really can feel it and it feels great.
If you're looking to improve performance or you've
dented your current muffler beyond recognition, you should have
a look at the Dynomax exhaust. We've seen it on the streets for
as little as $120 and it's worth every penny. Dynomax also makes
systems for most other Jeep applications, as well as many other
Dynomax Performance Exhaust
500 N. Field Dr.
Lake Forest, IL 60045
3250 Morrow Road
Birmingham AL, 35235
3465 Dialo Ave.
Hayward, CA 94545