I am having a 3 1/2 inch Diam lightweight single groove underdrive pulley machined up from billet steel for A series motors. Standard pulley is aprox 5 1/2 inches diameter, the 3 1/2 inch diam will spin the water pump and alternator at lower rpm than std pulley meaning power gain and less cavitation in the water pump at high engine rpm.
The 3 inch diam is approx same size as original Datsun works pulleys.
To keep costs down I have had these costed based on a run of 10 units, If anyone is interested in having one of these pulleys the cost is $225.00 plus postage.
8 units are up for grabs.
Reply if interested.

wouldnt water cavitation be worse with one of these cause they will be spinning even faster?

please forgive my ignorance and educate me.

The smaller the drive pulley the lesser the rotation of the subsequent pulleys.

If the pulley were over-sized you would speed things up.

Quote:

with an underdrive crank pulley, the alternator and water pump will spin at a lower RPM in relation to the engine rpm. Worth noting that the alternator will start producing charge at a higher engine RPM as a result. e.g std charge starts at ~ 1500 engine rpm, when being driven via a undersize crank pulley, the charging will occur around the 2000 rpm there abouts. Ideally underdrive pulleys are suited to high RPM engines when you want your alternator and water pump to operate at more realistic speeds.

ahh cheers Chris and Benny i had it all backwards, long day at work.

Deleted my stuff so as not to be confused with what beaufort is offering - sorry mate.

does look sexy

I am interested..

What about machining a common tooth pattern into it for firing a crank sensor? I.e. something like the 36-1 that is needed for running a MegaJolt ignition controller?
If not needed it is simply not used but otherwise makes the pulley a hell of a lot more useful!

Just a thought..

Underdrive
Think of it this way, underdrive means to slow down. Underdrive crank pulleys are designed to slow down engine accessories and reduce parasitic loss.
Crank pulleys, attached to the outside of the crankshaft, are the source of power for a car's accessories. The alternator and water pump are belt driven units, attached to the crank pulley, that use horsepower from an engine to provide their own services. This draw of power by these accessories is called parasitic loss. Underdrive crank pulleys increase an engine's throttle response and horsepower by reducing the power required to drive these external accessories. By replacing factory pulleys with smaller diameter units, the accessories are slowed enough so that their performance does not suffer, but just enough so that more horsepower is sent to the wheels and put to the ground and also benefit from increased accessory life and also deliver better fuel economy.

I'd be interested but the price is much too high (for my budget).

Is there an option for an aluminium version? I'd be keen on one of those I reckon.