Searched around and couldent find what belt size i need when i do the Dual Altnator pully upgrade.



and lets see your upgraded altenator!!

 

no one knows?


makes me wish icemark was still around : (

 

It depends on the diameter of the double pulley you want to use. I have a 54mm (under drive) Atkins double pulley for my FD alternator that required custom length belts. I just went to kragen and tried a bunch until I found a size that fit. If you get a "Higgi" pulley (the one w/ the rotor on it), one of Japan2LA's, or another similar one around 45mm on the inside of the belt path, you can use stock length belts.

This is with the Atkins pulley. I don't recommend it since the alternator spins way too slowly at idle speeds. I've got a smaller pulley that needs to make its way on soon here.

 

i just got this one

https://www.rx7club.com/2nd-generation-rx-7-1986-1992-parts-194/100amp-fd3s-alt-upgrade-s5-89-91-fc3s-na-tii-package-deal-865418/


but i notice you have one belt on yours. so whats the point of the double pully?

or do you have to do some more modding to actauly run dual pully on it?



p.s. thanks so much for an answer.

 

He is running two belts, its a dual belt pulley. It replaces the stock pulley.

The point of running a dual belt pulley is to prevent the waterpump from losing contact with the belt at high RPMS/load since with a single belt the water pump pulley WILL slip on the belt.

 

oh i see it now, hmm, ill have fun trying to find a belt size that works.

 

still need help on this issue.


so will i have to replace the other 2 pullys with dual pullys?

im just so confused.

 

You only need a dual pully if you remove the air pump. The second belt will take up the spot on the main pulley that the air pump belt leaves vacant.

If you remove the air pump there is one less belt on the water pump, which means less contact on that pully. So it will slip causing the water pump to work improperly, two belts connecting to the alternator means two belts connecting to the water pump which means it won't slip.

 

well my NA s5 motor is stock, i jsut want to upgrade to the FD alt for more volts, and the one i orderd had the dual pully on it.


so i want to keep my air pump and everything, just run dual pully on the alt.



wish someone had a write up on this.

 

Put a belt on like normal, leave one of the dual alt slots empty.


Done.

 

So when it comes to what is supposed to be an "upgrade" the pulley choice is either one in which overdrives or one in which underdrives?

 

Underdriving the pulley makes the alternator work less thereby reducing the alternators power robbing. It also means you get crappy voltage at idle.

 

If the old pulley was redrilled to fit the newer F6 alternator I guess that would be the best avenue to take. Also, I wonder if replacing the positive wire connected to the alternator with a thicker guage would be beneficial to an S4 alternator.

 

guess thats what ill have to do

 

The pulley shown in your link is one of the ones Japan2LA had made recently. I have the same pulley waiting to go onto my alt, and it's small enough to re-use the stock belt. The belt contact surface makes roughly a ~45mm diameter, which is what the stock pulley is. The main pulley to alternator pulley ratio of 2.08 will be maintained (the FC main pulley is ~90mm ID). FDs use this same ratio, so you won't be spinning the FD alt any faster or slower than it was intended. I had a 3rd gen guy measure his main pulley with calipers, then compared it to my own measurements of a stock FD alt. pulley . The FC FSM has the ratio spec, but the FD FSM doesn't mention it.

 

^pretty much have no idea what you said besides the measuring parts. but i guess ill some how have to find a belt that works i guess.....

 

There is no idle voltage issue with my pulley... It is NOT an underdrive pulley.. It is made for S4 and S5 FC3S owners who want to upgrade to the 100amp FD alternator... making this a bolt on swap with only minor wiring modification for S4 owners..

Want to use it with a smog pump, then you only run the one belt

No smog pumo, then run 2 belts...

Very simple...

 

k, i was just trying to figure out what size belt to use, im excited tho, finaily getting the right voltage.