Would underdrive, “power pulleys” free up some more power in the Impala?
In a word, no. The Impala has a 140amp alternator putting out 13.8 volts, which equates to a maximum output of 1932 watts, or 2.591 horsepower to run the alternator. So, accounting for ineffeciencies, your alternator is only pulling 3HP, at most (all accessories running). More often, it’s more like 1.5HP, where a 1/3 underdrive pulley would save you only about .5HP. Actually, this is the best case for the pulleys: in fact, the alternator will put out current to match demand at RPM’s above idle. This means that the only affect of the pulleys will be to reduce idle output from 75-100 amps to around 50 at idle. You would no longer be able to run all accessories at once without discharging the battery. In addition, there is more drain on the alternator once you start to run the motor because it has to recharge the drained battery. Also, being that they are made out of soft aluminum, the belt will actually wear the pulleys over time, causing belt slippage, belt mis-alignment, inbalances, an