What is the advantage to an underdrive pulley system? - Mustang Evolution

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Old 12-16-2011, 12:45 PM   #1
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What is the advantage to an underdrive pulley system?

2001 Mustang GT

The other day I noticed the harmonic balancer on my wife's car was shot. So this morning I jacked up the front end and removed the harmonic balancer. Went to NAPA bought a new one and installed it. When I went to install my new serpentine belt, it wouldn't fit. On closer inspection of the old harmonic balencer, and a neighbors input, it was concluded that the previous owner had installed an underdrive system. I went to Ford and bought a new OEM pulley for the water pump, so all is well now.

But now I wonder what the purpose of swapping out the pulleys is. There can't be that much of a drag on a 4.6l engine. And on my test drive I felt zero difference in performance.

So is this just snake oil sold to stupid kids?
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Old 12-16-2011, 01:26 PM   #2
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What is the advantage to an underdrive pulley system?

Supposedly underdrive pulleys usually are marketed as a performance enhancing item that increases the torque and horsepower output of an engine by reducing parasitic drag caused by belt-driven accessories, but more importantly by reducing the moment of inertia. Horsepower gains from underdrive pulleys alone are possible but usually less than 15 HP.
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Old 12-16-2011, 02:19 PM   #3
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What is the advantage to an underdrive pulley system?

Nope it helps sneak a couple horsepower out of the engine mostly used for racing purposes to gain a very slight edge, but for the normal everyday driver you will never notice 1-2 hp increase or decrease, by the seat of your pants.

No its true not snake oil but it is usually only done in high performance racing situations to get that little edge up.
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Old 12-16-2011, 02:37 PM   #4
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What is the advantage to an underdrive pulley system?

Because it's Ford?
As Henry ford was reducing the prices of his cars, thanks to improving assembly line, someone asked him how low he figured he could reduce the price eventually. To which he replied if he had total control of the parts market he could give them away for free, because they shook enough bolts off to keep parts makers in business and doing very well.

Too bad he was a NAZI-loving racist. He almost invented the "new economy" (where a business gives away 95% of everything and makes the money around the edges). Which may explain your after-market part.
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Old 12-16-2011, 03:35 PM   #5
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What is the advantage to an underdrive pulley system?

It does work. The engine pulleys run slower and the water pump works a bit slower lessening the parasitic drag of the water pump and the coolant, The alternator runs slower and cuts drag too. You may not notice any more or less power , but it does work. There is all kinds of drag on the engine as it pumps water and turns power steering pumps and other accessories. It may be 15 Horse Power difference. It's a proven way to reclaim power, Plus the engine and accessories last longer.
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