Greetings all.

I just got an upgraded alternator from an S5 NA, but alas all i have access to for dual pulleys is the Racing Beat underdrive. Granted, an S5 alternator @80 amps, under-driven to 64 amps is still more than the stock S3 alt @60 amps but not worth the "upgrade"

After scouring the internets I found the only source for this is BanzaiToyota. I sent him a PM and he hasn't got back to me.

What are our options out there for non-underdriven, dual sheave alternator pulleys??

Thanks in advance
~Geoff

 

Underdrive doesn't work that way. An 80 amp alternator is an 80 amp alternator, period.

That said, if you must have two belts, grab an alternator from a late 80s Subaru. I forget what model, exactly. You'll need the alternator and the pivot bolt, which is 8mm instead of 10mm. It's a Hitachi unit instead of a Mitsubishi, but the form factor is identical to FB and uses the same connector.

 

I use a 1999 Nissan Frontier alternator (70 amps). Bolts right on. The bottom spade on the alternator is the conector you need to turn it on and off.

pulley's are the same for duel pully purpases.

 

Well I already have the S5 alternator and already have the RB under driven dual alt pulley. If it doesnt decrease the amperage then maybe I should just use the RB pulley.

So what does an under driven pulley effect then, if not amperage?

 

Speed.

 

I'm just throwing this out there, not sure if its ever been tried, but would a pulley from an 80's GM 10SI alternator work? These alternators were on just about everything GM back in the 80's. Not high amperage really unless you have one from a Cadillac, but some came with a dual pulley on them and that pulley looks to be the same size as stock or close to it.

I have one of these at home as a 12V conversion piece on my antique tractor. Its from an 81 Camaro V6. Might be worth a try to take the pulley off and try it on the FC alternator I have in my 79? Would be a real cheap way to put a dual pulley on an FB with a stock alternator, without loosing out on valuable amperage at idle.

 

Well yeah that's what it changes but what is the effect of that change?

 

Just the speed of the alternator. The amperage is determined by the design of the alternator, the voltage is determined by the speed of the alternator. The power to drive it is determined by the electrical load. We regulate the voltage down to ~14v or so. Full-fielded, most alternators can easily generate over 50 volts given enough speed.

I can bring my engine's idle down by about 500rpm by turning my fans on. If I had an underdrive pulley on the alternator, it wouldn't be able to keep up even if it was full fielded, so it would pull idle down less. It'd drain the battery, too Plus, well, I'm not sure what RPM the alternators are good for.

(Note - I have the tiny single-sheave main pulley. 3" I think. My stock-pulley S5 alternator will still put out over 60 amps at ~1100 engine RPM. The fans pull it down from 1500ish...)

 

Sam at re-speed can hook you up, i ordered 2 and had them in a week.

 

Rotary Alternator Pulley

that is a non-underdrive pulley and has a rotor shape. i have already contacted them to ask. shipping to the u.s. is $14 since their shipping calculator never works.

 

Go to junkyard, find similar alternators on minivans (chrysler may work) and pull.

 

Sicker than snot!!!

 

Only problem I have had with the dual sheeve setups is that at engine speeds over 10K, no matter what tension you run on the belts, the belts will deflect at different rates and rip each other to shreds. Another thing to be mindful of is this will also put more strain on the front bearing if not properly adjusted. 2 belts at the same tension will put more side load on the e-shaft.

 

http://foxed.ca/rx-7/WAI%20PART%20DESCRIPTION.pdf

That is the part on many mopar minivans, etc. Any local alternator shop should have the pulley new, or a junkyard. Fits right on the mazda alternators. I have used one for years.