Serpentine belt is too big after installing upgraded alternator

This is a very misguided modification. Unless this is some unusual custom setup, there is nothing to be gained by installing a generator with a higher output. All generators need three things to operate. They need a magnet, (electromagnet, in this case), a coil of wire, and most importantly, movement between them. For this reason, they are all very inefficient at low engine speeds, and this is why all testing requires the engine to be run at 2,000 rpm for a few seconds while the tests are performed. The only thing the smaller pulley will get you is the ability to get closer to the designed-in maximum output current at idle. The trade-off, since these are designed to operate within certain rotational speed limits, is the potential for the rotating field winding to fly apart or expand and hit the stationary "stator" winding, and lock up.

The second important point to be aware of is all AC generators will only develop exactly the amount of current needed by the electrical system, and to recharge the battery, and no more. If all of that requires 47 amps, you will only get 47 amps regardless if the generator's maximum capacity is 80 amps, 180 amps, or a thousand amps. Think of the water pump filling the municipal water tower. If the tower is full and the residents are using ten gallons per minute, the pump is going to move ten gallons per minute even though it might be capable of pumping 10,000 gallons per minute. Installing a pump with a 20,000 gallon per minute capacity isn't going to move any more water than that ten gallons being used.

Also be aware an AC generator is physically incapable of developing more output current than it was designed and built for. They are all self-regulating in that respect. I'm not real clear on what you meant by "overclocking". That refers to the digital clock circuit in computers. There is no such thing with a generator. If you have a 90-amp generator, which already has more output capacity than you'll ever need, there is no way possible for it to develop more than 90 amps. If that were possible, every generator would develop more and more current as engine speed increased. Batteries in Nascar race cars would explode from over-charging, but we know that doesn't happen.

In fact, of the three things I mentioned to generate current, we can't run alongside the car and change the number of loops of wire in the stator coils, (which is how larger-output generators are built), and it is not practical to lower engine speed once the battery becomes fully-charged. We don't increase engine speed when we want to run the heater fan on a higher speed. In fact, the only thing that can be easily adjusted is the strength of the spinning electromagnetic field coil. That is controlled by the voltage regulator and has nothing to do with engine speed.

If you turn on additional "loads" on the electrical system, that draws the battery's voltage down just a little, but enough to be detected by the voltage regulator. In response, the regulator allows more current to flow through the field winding. That creates a stronger magnetic field, and that increases the output voltage, (pressure), which translates into more output current. That higher current results in higher system voltage, then the voltage regulator readjusts for that again, and continuously as you drive. This would equate to the water pump keeping the water tower just at the "full" mark, without blowing the top off, regardless of how much water is being used at various times.

The bottom line is if you have a 90-amp generator, there is no possible way it will ever develop more than 90 amps. If you still need to use it on your engine, the people at the auto parts stores have listings for all the different belt lengths, widths, and number of ribs. They can look up the original belt to find its length, then they should be able to find one the next size shorter for you.

There is one potential hazard you should be aware of that mechanics might be unfairly blamed for. The only time an AC generator will ever develop the maximum current it was designed for is during the "full-load output current" test that is part of the standard charging system test. That test only lasts a few seconds but it can be long enough to blow the fuse or fuse link wire that is always in this circuit. The tester puts a very heavy load on the battery, and engine speed is increased to get the generator spinning at its most efficient speed. The voltage regulator sees the drop in system voltage, so it increases field current to get the output voltage back up to where it should be. It has to increase output current to do that, and that is the only time the generator will be running wide-open.

The standard generator for your vehicle is, in fact, a 90-amp generator. The fuse link is always selected at the factory based on the generator's rating, and for yours that is a 100-amp bolted-in fuse. That fuse will survive any system testing, ... Until you install a generator with a higher maximum output capacity. If you could actually find a 180-amp generator, and the full-load output current test is performed, close to 180 amps will be developed, and that will blow the 100-amp fuse. Before the mid 1990s, that fuse was a special fuse link wire spliced into the wiring harness and was usually not easily accessible or easily replaceable.

When multiple optional generator sizes were available during assembly at the factory, the output wire going back to the battery was always fat enough to handle the maximum current from the largest available generator, then, all they had to do was install the proper-size fuse or fuse link wire to match that generator. Your vehicle was available with an optional 110-amp generator. When those were installed, the fuse likely would have been a 120-amp or 125-amp fuse.

Wire # 15W in this diagram is of a large enough gauge to handle 110 amps intermittently, so it will also be fine with a 90-amp generator. It will not handle 180 amps. If you were to replace the 100-amp fuse with a 200-amp fuse, that will not protect that wire 15W.

All AC generators have at least six internal "diodes" which are one-way valves for electrical current flow. They are in two sets of three diodes. Those appear backward in the circuit when the engine is not running, and they are what blocks current flow and prevents the battery from discharging through the generator. It is not uncommon for one of those diodes to short. That will cut the generator's maximum output capacity to exactly one third of its rated current, but there will still be the diodes in the other set to prevent current flow. Most of the time there are symptoms that lead to the replacement of the generator, but if it goes undiagnosed or ignored, it is possible for a diode in the second set to short too. That would result in a dead short across the battery, and really high current flow through that 15W wire. The wire would burn up and start a fire before the fuse would blow. When doing this type of modification, that wire has to changed as well as the size of the fuse protecting it.

This is the type of modification a mechanic will never do due to potential lawsuits. Lawyers and insurance investigators love to find things like this, as well as modified suspension ride height. They will find the non-standard wiring and will usually use it to avoid paying a claim. That is why no mechanic wants to be involved with this. In fact, any parts for these types of modifications will always come with the standard, "For off-road use only" disclaimer.

If you look at the 110-amp generator for your vehicle, you'll see it comes with the same size pulley as the 90-amp unit uses. The higher output capacity comes from adding just a few inches of heavy wire to the stationary stator coils. That adds only one or two extra loops of wire to get that higher capacity. That additional copper wire only costs a few cents, but then they'll need diodes that can handle that higher current. All told, it costs perhaps five dollars more to produce the 110-amp unit, but they'll charge a whole lot more for it than that. Sometimes they use the same lower-current diodes but they put them in beefier aluminum heat sinks. The engineers know it isn't going to develop any higher current except for those few times when a full-load output current test is performed, or when you're running the heater fan on "high" at the same time you're running all of the power windows, power locks and mirrors, head lights, wipers, and radio all at once. The more massive heat sink will slow how quickly the diodes heat up and short.