underdrive pulleys

[Asa]

The first of the aftermarket parts to be installed was the Steeda underdrive pulley kit. The kit includes an SFI crankshaft pulley, water pump pulley and alternator pulley. The reason underdrive pulleys add power is that they reduce parasitic drag on the engine. Drag, or friction, is created by engine accessories and by slowing the speed of the accessory drive belt, the accessories spin slower, thus reducing friction or parasitic drag. The result is usually increased power to the wheels.

ok, so because these are being turned slower, does that mean they work less efficiently? like instead of the water pump flowing X cfm at 3000 RPM of water it flows Y cfm at 3000 RPM where X<Y?
i'm just wondering because if you are getting more HP by starving your engine of a necessary system, isn't that ...... stupid?

 

[StrangeRanger]

Not always. The stock pulley system is for the "normal" user, which none of us are. If you stick bigger gears in the car, you're turning more revs than "normal" and the underdrive simply reduces the accessory speed to something like the original. If you have improved the intake, exhaust or camshaft, you're likely to be using more revs. Same problem, same solution. The stock pulleys are designed so the car can idle in a traffic jam in Phoenix in August without boiling over. How many of us need that much in either charging or cooling capacity?

 

[Asa]

ok, that makes sense, but is it possible to do some damage on an otherwise stock car? i'm personally not worried about it, but it seems like this is a common mod, and others do it and maybe a K&N, plus dual exhaust and nothing else
just wondering

 

[Anonymous]

The stock pulley system is for the "normal" user, which none of us are.

LOL

 

[Anonymous]

can u even get a kit for a 250-200

 

[Anlushac11]

8)

Also keep in mind that most water pumps will flow fine at idle and low rpms, but as rpms build you start to lose flow effeciency to the point where you can start getting cavitation. When caviation occurs you are not moving water as much as creating a air pocket behind impeller blade and this kills water flow.

When you run underdrive pulleys you lower the rpms of the water pump. After market high performance water pumps have HD bearings for high rpm use and a specially designed impeller to reduce chance of cavitation.

 

[Anonymous]

I saw a kit for a waterpump in a magazine(can't remember which) that riveted a plate to the back of the water pump vanes to improve pump efficiency. This could help at low and high rpms, now if we can fit one to our pumps!!

 

[Anlushac11]

8)

I just went and looked at waterpump off my '80 and it sorta has a flat plate on the back. The backplate is flat and the fins for the impeller are cut and folded up from the back plate.