Will a dual Alt. pully provide less volts?
 

I am concerned that it might not get full power to the fuel pump. I had that setup on my last 87 T2, but didn't have it long before someone pulled out in front of me. Now with my 88 T2 project, I am thinking of doing it again, but wonder if it gives full amps or whatever to the fuel pump? I would sure hate to not get all the fuel I should. Thanks for any imput guys!

the dual pully is a bit smaller so at idle the volts might drop a bit. but they will be fine once the rpm is up, and better for the car from 4000-redline

A dual alt pulley will do just what it says. It gives you twice the output from your alt. So it will give more voltage to your fuel pump. O.K.

ehhh wrong....I dont think you even seen one. Just because it says dual doesnt mean it doubles the voltage!.. its dual because it will able you to run 2 belts and prevent belt slippage. Its also undriven so it slows the waterpump to prevent CAVITATION.

You are right that he is wrong... but you are wrong too. The size of the alternator pulley doesn't have anything to do with the speed of the waterpump. That would be changed by changing either the pulley on the eccentric shaft or on the water pump, or both. The dual alternator pulley uses 2 belts to prevent the belts from slipping on the waterpump pulley if there is no airpump present.

Brad

Ok, the dual alt pulley is an underdrive pulley. it underdrives the alternator by 13% or so. If you use that pulley by itself, it shouldnt be a problem. I have the RB main and alt pulleys, and my headlights dim at idle, but above 2K rpm everything is fine. You shouldnt have a fuel pump problem, as the voltage will only be a little low at idle, not under enouogh boost to cause a problem. Also, if the current draw is more then the alt can supply, it will start draining the battery. You will not have to worry about not getting enough voltage to the fuel pump, unless your battery is dead.

This also depends on which dual pulley you have. Mine does not underdrive the alt. It is a stock sized pulley that has 2 grooves for belts when you eliminate the airpump. This is so you do not get belt slip on the water pump due to the angle of just one belt running across it. Reason I know mine is not an underdrive pulley...I measured it with a stock one at the sides and the valley of the pulley with a micrometer.

Mazdaspeed7 is also correct though in that fuel pump voltage will not be affected at boost levels since you have full alt power under boost due to rpm's

Thanks for the imput guys! I will be taking off the air pump soon and getting it!

Just to clear things up in my head

If the alt pulley is underdriven it means it is has a bigger diameter, if it is over driven it means it has a smaller diameter correct?

If the pulley has a smaller diameter the pulley will increase the number of revolutions it can do and therefor overdrive the alt, is this correct?

rx7_turbo2.........

Your thought process is right-on dude.