Do I need a larger serpentine belt if I get a larger alterator pulley?

[jpk]

I have all stock pullies on my engine and accessories today. I'm putting a new alternator on and I have read the recommendations to use a larger pulley to slow it down and extend the service life.

I already bought a new belt in stock length. Will it fit if the only pulley I increase size on is the alternator? Thinking of getting a 3.2 pulley. If the belt won't fit, I think I will just stick with stock pulley.

Thanks!

 

[jbou91]

I believe you only change the alternator pulley when you do a lower crank pulley (to prevent from over-spinning). Otherwise you'd be messing with the output of the alternator and it won't make shit at idle.

 

[bubblehead93]

if you search around on the forums (and I think Cobrabob's FAQ) there is discussion about this and that "bone stock" the alternator gets spun a bit fast... that being said... there are other alt pulley choices than 3.2 (i.e. between stock and 3.2) which is normally associated with running a 4# lower... I recently went from a 3.2 to a 2.9 when I swapped out my PA alternator for a Mechman, the difference is about 1" in circumference, needed to go with a shorter belt to keep the tensioner in its sweet spot...

r/
Andy