Text below is originally taken from the TCCoA technical articles written by DanU. This has gone through our technical articles submission process at www.midwestthundercats.com/forums/
and was corrected and added to using suggestions of our group.
We confirmed all prices, websites and phone numbers as being current as well.
Overdrive pulleys are for supercharged applications. There's not much to it. What you do is purchase a smaller pulley for the supercharger, which in turn spins the supercharger faster thus forcing more air into the engine. Be warned that this will increase intake air temps, which can lead to detonation and is also subject to the law of diminishing returns. (If the first 10% gives you 40HP, the next 10% won't give you another 40HP.)
Under Drive pulleys are for naturally aspirated applications. They consist of a smaller crank & larger alternator and water pump pulleys. The larger diameter of the accessory pulleys means that they’re spinning slower, and the smaller pulley on the crank makes up for the belt length difference. The slower spinning accessories reduce drag, thus drawing less power away from the crank. You retain the factory belt with under drive pulleys.
There are two types of crank pulleys that you can get with underdrive pulleys. The first is a "piggyback" style, which reuses the stock crank pulley as a harmonic balancer. These kits are cheaper, but add an additional rotating mass in front of your crank. These are also the only option for those of you with a 3.8 or 5.0 motor. The second type is the "standalone" style. These kits, while more expensive, integrate the harmonic balancer onto the crank pulley itself. You don't reuse your factory crank with these kits. These are overall the best option from companies like Steeda or ASP. On the SC 3.8 motors there are some other issues to be aware of that are addressed below.
For those of you who've been considering this mod here is a quick rundown on what to expect as far as installation:
Installation for the 4.6L is straightforward. You'll need an impact wrench and a crank pulley puller to be able to complete this job. You can purchase or rent either of these items from your local automotive store. The alternator nut is 23mm, and the crank bolt is 18mm. Be sure to use a 6 point socket to avoid rounding off the edges of the nuts/bolts.
Depending on the size of your impact wrench, you may be able to just remove your electric fan (where applicable) or you may need to move your radiator. If needed, you can remove the top mounting brackets for the radiator, and just push it up about 10". Put the radiator on blocks to hold it up while you work. It is also suggested that you put a piece of cardboard between the AC condenser and the radiator to protect them from rubbing. This saved a ton of time over removing the radiator.
On the supercharged 3.8 you can make use of under drives as well. There are a couple of things to be aware of, however that differ from the 4.6. The crank pulley and harmonic balancer are balanced as a unit from the factory. Meaning that if you just unbolt the stock crank pulley and bolt on the UD crank pulley you are going to have some balance issues. If you’re putting on UD’s you're probably putting out more power than stock, so replacing your stock balancer isn’t a bad idea anyway. As a side note, the bolt that holds the balancer onto the crank is 14 x 1.5. The bolt for the SC is discontinued, but you can use the bolt from the mustang 3.8.
Installation: You will have to remove your fan but not your radiator. If you go with the aftermarket HB then all you have to do is bolt on the UD crank pulley. The water pump is very easy also, just 4 bolts. You can get the alternator pulley off without actually removing anything with a breaker bar, a strap wrench, and a friend. Just wrap the strap wrench around the pulley to keep it from moving while your friend breaks the nut loose. Installation is just the reverse. If you keep the stock balancer then you need to have it and the UD pulley balanced as a unit before you install.
After the install, you should notice a big improvement in the low end, along with mid and high end acceleration too. Depending on your tranny condition and tires, you may be able to spin the tires from a complete stop and even chirp when shifting into 2nd after the pulley installation.
Temperatures have been noted to increase a small amount after pulley installation, but nothing critical at all. Usually the temperature spikes only occur when sitting idle on a hot day. This can be alleviated with a lower temp thermostat and lower fan kick-in from a chip.
Charging problems should be non-existent unless you're running thousands of watts through your sound system at idle. If you're really paranoid, you can shift into neutral while stopped, thus raising your RPM's a bit and returning you to full charge. Or you can add an overdrive pulley for your alternator that will compensate for the other pulleys.
Overall under drive pulleys may not make a huge difference in performance, but they're a relatively cheap mod that makes a difference none-the-less.
March Performance (734) 729-9070 - http://www.marchperf.com/
Auto Specialties (877)928-8678 - http://www.autospecialties.com/
Steeda (954) 960-0774 - http://www.steeda.com/
Supercoupe Performance (513) 697-6501 - http://www.supercoupeperformance.com/
Piggyback Part Numbers & Prices (4.6L):
ASP - ASP527728 $129.95
FRPP (Blue Anodized March Pulleys) - M-8509-D462 $149.95
March - 1150 $129.95
Standalone Part Numbers & Prices (4.6L):
ASP - ASP527328 $199.95
Steeda - 701-0001 $169.95
March - 1185 $199.95
Standalone Parts Prices (3.8L)
SCP - $180
Nitride = ASP520125
Zinc = ASP620125
Hard coat black = ASP820125
Installation Guide: (4.6L)
Last Updated 8/10/03 0430AM