Pulley Performance

[MMG1989]

I have a question for you guys I been hearing alot of people on the site talk about changing out their pulleys and i was wondering what actually does that do with changing them out does it increase a little horsepower?

[slickster]

An Underdrive pulley refers to an aftermarket crankshaft or accessory pulley (such as an alternator pulley) that is designed to drive a vehicle's accessories at a slower rate than stock. Underdrive in general means the input rate of rotation in a system is greater than the output rate of rotation. However, an underdrive pulley is considered to be an accessory pulley that is larger than the stock pulley, or a crankshaft pulley that is smaller than the stock crankshaft pulley, even though the accessory may not necessarily be underdriven with respect to the crankshaft pulley.
[edit]Typical Usage Scenario

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. Independent dyno tests have shown up to 15hp increase at the wheels after installing an underdrive pulley (see references). [1] [2]
[edit]Usage Concerns

Poorly designed pulleys can have severe side effects because of too much underdrive of the alternator, power steering, and/or air conditioning units, which are not spinning fast enough. These lead to dips in alternator voltage, power assist, and air conditioning effectiveness that may be noticeable, especially at idle. The headlights may dim when coming to a stop, or the stereo may lower in volume, for instance. Too much underdrive for a race car is not much of a concern, but for a daily driven vehicle it can be a major annoyance.
Changing the original crankshaft pulley can have negative effects if the replacement pulley is not manufactured properly. A crankshaft or accessory pulley that is not machined or balanced properly can cause severe damage. For most American V8s a harmonic damper is necessary to absorb crankshaft vibrations. Earlier V8's kept the pulley and damper as separate components. Most late model V8s now integrate the damper and the pulley into one part. In general, for small displacement engines (4.0L and under) the original crankshaft pulley only serves to quiet noise vibration and harshness (NVH) heard in the occupant compartment.[citation needed] plus you might need a tuner to bump the idle

[SC Cheesehead]

I'd say 15 hp is a bit optimistic on our cars, more like 5 to 7, IMO; but yeah, they do help.

Engine definitely spools up faster, and feels like it pulls stronger in mid-range.

Keep in mind, though, if you ever decided to go S/C you'll need to revert back to the OEM pulley set up.

[magindat]

Wasn't there talk about older ones killing the oil pump because of vibration?

[ctrlraven]

Wasn't there talk about older ones killing the oil pump because of vibration?
I hope not. lol

I have SC Cheesehead's old Steeda ones that ImpalaSlayer took off when he did his Eaton swap.

[SC Cheesehead]

I hope not. lol

I have SC Cheesehead's old Steeda ones that ImpalaSlayer took off when he did his Eaton swap.

If it ain't blowed up yet, prolly won't... ;) -----> :D

[RF Overlord]

Wasn't there talk about older ones killing the oil pump because of vibration?That was one specific brand of pulley (not Steeda) that was improperly installed.

[screamn]

That was one specific brand of pulley (not Steeda) that was improperly installed.

Please post which specific brand it was so I and new members will know to stay away from getting it!

Thanks in advance.

[cougar9150]

I had steeda's on my 2nd MM when I 1st bought it. Engine had a nasty vibration and was leaking oil at the crank (car bought over the phone/email and did not arrive as advertised).

When I pulled the motor to fix some the oil leak and and other issues the pulley was almost falling apart. The outer ring was almost fully separated from the center hub, took it off, threw it in the garbage, and bought a used OEM one from a member here. No problem or vibrations since.

Not saying it was Steeda's fault as I believe it was improperly installed along with several other items on the car.

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