Re: Undersize Pulleys

["Andy Radin" <fourfa@xxxxxxxxxxx>]

"A question was raised as to how undersize pulleys can increase 
performance, and how these pullies might do so on the road but perhaps 
not on the dyno...the dyno will usually only give steady-state 
conditions, the accessories are not accelerating, and so little or not 
increase in horsepower is seen. 
Robert"

Well, in fact all of the accessories (power steering, water pump, air 
conditioning, alternator) are pumps of some sort (let's call electricity 
an electron fluid), and pumping fluids requires force.  Thus they draw 
horsepower linear (roughly) with speed (i.e. more power at high RPMs).  
Underdriving them will free up power, accelerating or not, dyno or not.  
On some cars, this can be worth a lot (Nissan 300ZX - 20 HP) or not 
(Nissan SE-R - 3 HP), depending on accessory load.

Of course you have to be damn sure there's excess cooling capacity 
before underdriving the water pump.

andy r.

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