’93-’98 Grand Cherokee V8 Under-drive Pulleys:
By: Scott Mueller
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 under drive compared to stock and found that by using all three pulleys, March and Jet were under driving 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 under drive 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 under drive 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:
14840 N. 74th St.
Scottsdale, AZ 85260
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 under drive 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.