GK
01-20-2002, 11:10 PM
UNDERDRIVE PULLEY
Underdrive pulleys. Do they work? What are they? How do they work? What kind of increase will I see? What are the drawbacks to using these pulleys? Well, in this article, I will attempt to answer these questions.
First, what are they? It is a system of different sized pulleys that replace the crankshaft, alternator, and sometimes the water pump pulleys.
Second, how do they work? By changing the size of the pulleys, you can slow down the speed of the accessories. This takes less horsepower to turn them. The engine then uses this “free” horsepower and applies it at the rear wheels. You will also need a shorter belt(s).
Third, how do they work? By making the crankshaft pulley smaller, you turn the accessories slower. This is what they call the “drive” pulley. Think about a ten-speed bike. When changing from the bigger sprocket to the smaller one, it is easier to turn the crank pedals. This is about a 7% gain alone. Now, when you increase the size of the alternator and the water pump, the “driven” pulleys, you slow the accessories down even more. Again, back to the ten-speed bike. The sprockets on the rear tire, the bigger the easier it is to pedal the bike. These pulleys will “free up” about 3% more.
Fourth, what are the drawbacks to using these pulleys? In a two-pulley system, crank and alternator, there are no drawbacks. When adding the water pump pulley, sometimes the alternator spins too slowly. And over time you will kill the battery and/or alternator. I have seen this many times on the Ford 5.0l engines. They would kill the alternators. In the GM engines, I haven’t seen this yet.
Finally, what kind of increase will I see? The aftermarket claims 10-15 hp at the rear wheels. When I put them on my ’95 Camaro 3.4v6, it dyno’ed 10.5 hp at the rear wheels. One of the car magazines put them on a car and gained 0.14 e.t. in the quarter mile.
Underdrive pulleys. Do they work? What are they? How do they work? What kind of increase will I see? What are the drawbacks to using these pulleys? Well, in this article, I will attempt to answer these questions.
First, what are they? It is a system of different sized pulleys that replace the crankshaft, alternator, and sometimes the water pump pulleys.
Second, how do they work? By changing the size of the pulleys, you can slow down the speed of the accessories. This takes less horsepower to turn them. The engine then uses this “free” horsepower and applies it at the rear wheels. You will also need a shorter belt(s).
Third, how do they work? By making the crankshaft pulley smaller, you turn the accessories slower. This is what they call the “drive” pulley. Think about a ten-speed bike. When changing from the bigger sprocket to the smaller one, it is easier to turn the crank pedals. This is about a 7% gain alone. Now, when you increase the size of the alternator and the water pump, the “driven” pulleys, you slow the accessories down even more. Again, back to the ten-speed bike. The sprockets on the rear tire, the bigger the easier it is to pedal the bike. These pulleys will “free up” about 3% more.
Fourth, what are the drawbacks to using these pulleys? In a two-pulley system, crank and alternator, there are no drawbacks. When adding the water pump pulley, sometimes the alternator spins too slowly. And over time you will kill the battery and/or alternator. I have seen this many times on the Ford 5.0l engines. They would kill the alternators. In the GM engines, I haven’t seen this yet.
Finally, what kind of increase will I see? The aftermarket claims 10-15 hp at the rear wheels. When I put them on my ’95 Camaro 3.4v6, it dyno’ed 10.5 hp at the rear wheels. One of the car magazines put them on a car and gained 0.14 e.t. in the quarter mile.