This is a general question. ASP recommends a 89.5" belt when using just the underdrive crank pulley, but then a 90.0" belt when using the underdrive crank pulley AND overdrive alternator pulley. Correct me if I'm wrong, shouldn't an overdrive alternator pulley have a SMALLER diameter to spin the alternator faster, hence needing a SHORTER belt??

A smaller driver (crank) pulley will spin the driven accessories slower. But when you put a smaller pulley on the accessories, they spin faster.

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What am I missing here?

 

No, and underdrive accessory pulley will be larger.

 

Then that would make the accessory spin slower, don't you want the alternator to spin faster to produce more amps if you have an underdrive crank pulley?

 

it is a typo on the asp site... i have the gates 060895 on my truck now... i have the od alt pulley and the ud crank pulley

 

the underdrive crank pulley is smaller diameter than stock. the overdrive alternator pulley is also smaller in diameter than stock

 

and by underdrive alternator pulley you mean overdrive correct?

 

By definition, an underdrive accessory pulley is larger than stock so it spins slower, and an underdrive crank pulley is smaller than stock so it spins all of the accessories slower. The under in underdrive refers to reducing the speed. So yes, the correct term would be overdrive alternator pulley, which is smaller than stock, and thus spins the alternator faster.

So the same questions remains, why a longer belt with the smaller pulley? Typo?

 

ASP replied and said the belts in the posted link are for their underdrive alternator pulley which is larger than stock to spin the alternator slower. Not sure why anyone would want to underdrive their crank AND alternator pulley.

 

I'm going through this delimia right now, and based on your final answer from ASP, what is the final part number for the combination of Underdrive crank & overdrive alternator. Because I don't see the answer to the original question, which belt do you use?! The Gates K060895 which ASP refers to "Accessory belt w/ Crank only"?

 

Maybe so it doesn't go kaput when spinning the engine at 7000rpm?