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There are currently two pulley kits on the market for the 5.2L/5.9L Magnum
engines, one by March and one by Jet. They both include a
smaller crank pulley as well as larger water pump and alternator pulleys.
Unfortunately for mid-'98 and newer Magnum engines the water
pump pulley is no longer bolted onto the shaft and removable, instead it
is a direct part of the pump shaft. This means that the water pump
pulley cannot be changed to the larger one in the kit. Actually this turns
out to be a blessing in disguise, since unless you are racing only, you do
NOT want to use all three pulleys.
I computed the precise ratios of underdrive compared to stock and found
that by using all three pulleys, March and Jet were underdriving the water
pump by 34% and 37% (respectively), and the alternator by 46% and 48%
(respectively). Unfortunately these ratios are WAY too steep for a street
driven vehicle IMHO.
Even if you could, using all three of the pulleys from the Jet (or March)
kits would result in about a 35% reduction in water pump speed and a
nearly 50% (unacceptable to me) reduction in alternator speed. That much
speed reduction on the alternator would mean that the battery would begin
discharging at idle with any accessories on, and lowering the water pump
speed that much could cause overheating, especially in stop and go traffic
with the A/C on, or possibly under towing conditions as well. In fact both
companies specifically recommend against towing if you use their full
kits.
On the other hand, by using ONLY the crank pulley from either of their
kits, you would end up with a total underdrive for ALL accessories of only
23% or 25% for the March and Jet pulleys respectively, figures which are
acceptable and which don't lead to charging or cooling problems.
The March pulleys are machined billet T6 aluminum and clear powder coated.
The Jet pulleys are machined billet steel and anodized black. I prefer
black for the totally stock look, that way the dealer (or anybody else)
would never know it was changed. I was also concerned about the durability
and longevity of the aluminum. The drive belt is highly abrasive, and over
time the belt will wear the pulleys down. Also aluminum particles will
transfer to the abrasive belt causing it to slip. There is no OEM
manufacturer I am aware of using aluminum pulleys on a production car for
the simple reason that they aren't durable.
Bottom line: I decided that the only way to do an underdrive setup
correctly would be to change only the crank pulley, and use only a steel
(not aluminum) one. This meant I wanted only the crank pulley out of the
Jet kit.
Rather than having to purchase the entire pulley kit, and realizing that
Jet does not make their own pulleys, I ended up researching who made the
pulleys for Jet and found I could purchase the same crank pulley alone
from a distributor:
Evergreen Performance
14840 N. 74th St.
Scottsdale, AZ 85260
(800-498-6951) orders
(602-443-3333)
(602-443-3636) fax
<http://www.airaid.com>
<http://www.4evergreen.com>
<mailto:sales@4evergreen.com>
Ask for John Levits (ext. 210), tell him I sent you, he's a friend of
mine.
The crank pulley is the same one Jet sells in their kit, and is machined
from steel and treated to a black oxide coating. Besides being the most
durable, it also has nearly 2.3% greater underdrive than the March crank
pulley, and it has the advantage of looking 100% stock under the hood. The
pulley is attached to the harmonic balancer by six 1/2" bolts which are
very easy to get to from underneath.
Since the new pulley is smaller in diameter than stock, a shorter belt is
required. The Grand Cherokee V8s (both 5.2 or 5.9L) use a 7-rib 25mm x
2265mm belt stock, which needs to be changed to a shorter 25mm x 2190mm
belt (two sizes smaller than stock). This belt is just a slight bit
shorter than it should be to be perfect, meaning the belt tensioner ends
up near the end of its travel range with this belt installed.
Unfortunately the next size belt up or down is way off.
To make this belt work perfectly I removed the belt tensioner and slightly
relieved the alignment tab with a file causing the tensioner position to
change slightly when installed. This allows the tensioner to be in the
proper travel range (indicated by an arrow on the tensioner) for this
belt. For replacement belts, I recommend Gates, they make OEM quality
belts and their part number K070855 is the 25mm x 2190mm belt I used. Note
that many of the aftermarket belts found at discount parts stores are of
vastly inferior quality to stock, as such I only recommend Gates or
Goodyear for replacement belts.
Note that by installing a new OEM tensioner, plus the stock belt and
pulley, the vehicle can be returned to stock in about 15 minutes time.
I tested the vehicle and with the headlights and rear defog on the system
retained full voltage at idle, meaning the alternator was working well
enough to maintain battery charge. This is important for winter driving
under stop and go conditions. I did not measure the HP increase, but
estimate a few HP are gained, and the engine may rev a bit quicker as
well.
Scott.
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