Can't find the right belt size??

[03SonicSVT]

Let me start of by saying I have read the stickies and all of the belt size guides.
i am running a billet flow 2.93 upper and metco 6 pound lower with 100mm idler. Based on the guides, I need a 78.5 belt. I mistakenly got a 79.5 and it is WAY to short.
does anyone else know what size belt is needed?

 

[Givens]

What size is your alternator pulley?

Also have you swapped out you aux idlers with aftermarket or are they stock

Hurry before someone chimes in and tells you to run a string around the pulleys!!!!

 

[03SonicSVT]

I have the stock alternator pulley. I have the billet glow 4 piece idler set with the one 100mm idler.
I think I found that a 81 1/8 belt is what fits. I just tested 6 of them to see what looked right. It's just strange since the guides recommended a 78.5 for my set up!

 

[Givens]

Yea it says 78.5 but you have to add for the other idlers

Add 1" with a Metco Auxiliary Idler
Add 1" with a 3.20" Alternator Pulley
Add 1.5" with a 3.50" Alternator Pulley
Add 2.0" with a 3.70" Alternator Pulley
Add .5" when changing from a 90mm Idler to a 100mm Idler

I come up with 80, but if the 81 fits seems long from what I've seen

 

[NateDogg]

I have a similar set up, and the 81 is to long.

I have 3.1 upper, 3 100mm, 1 90mm and a 6lb lower. Not sure about the Alt.

I just ordered an 80.5 and a 79.7. Hopefully one of those fit right.

 

[Shadow Grey 03]

I'd put a 3.5 alt pulley on there.