Belt length - 3.5 and 3.25 Whipple pulley

[slow98cobra]

Alright, found several threads around this topic but just looking for a definitive answer from the brain trust of SVTP. I keep seeing grab a string, look at stangshiftergaskets, reference Metco, look at billetflow’s website, etc. I can’t seem to come up with the same answer to double check. My setup will not be something new that someone else doesn’t already have or have tried. Just need a straight answer.

I have a stock lower, the 4 piece billetflow idler set and need a belt(s) for a 3.5 and 3.25 Whipple pulley.

What belt are you all running on that setup(s)?

 

[Roush6018]

you need to measure your ALT pulley diameter too. i have a J2 FAB alt , stock lower, stock upper on a eaton and billet idilers. i tried the stock size belt. it didnt work, too tight, but it showed me if i needed shorter or longer. you can install a supercharger belt too tight, you need to check that your tensioner is in the middle of the notch with a NEW belt installed, after 2k-3k miles the belt is worn in and could show different on the tensioner notch.

so the stock eaton pulley is 3.65" and you should find a belt to work with your 3.5" pulley first. so find the P/N on your current belt and then order the next size shorter belt to see how it works with your 3.5" pulley. install the shorter belt and check the tensioner notch. if its too loose then try the next size shorter belt. install the next shorter belt with your 3.5" pulley and then check the tensioner notch, if its good then you found the right size.

the stock cobra belt is Gates 080751 this is a 75.08" belt
my car is perfect with a Gates 080765 is a 76.50" belt. (on the LMR chart 77" link)
The LMR website is where i found this, they have a great chart!!!!!!!
you should try a 74" belt first the Gates 080740
(when using the LMR chart , choose the 74.50" link) (080740)
(if you choose the 74" link it will order you a 73.5" belt) (080734)


so my car needed a 1.5" longer belt with my J2 alt (stock 03 cobra ALT pulley ) and some billet idilers. stock upper and stock lower.

 

[MG0h3]

Gates 080780 for the 3.5.

Ran the same with a 3.75.


Currently running a 080765 with a 2.9 upper.

All with stock tensioner. Stock lower. Typical idler setup like you mentioned mentioned


Sent from my iPhone using svtperformance.com

 

[cj428mach]

The Whipple instructions for my old 2.3 had the belt lengths listed in it. Have you reached out to Whipple?

 

[slow98cobra]

The Whipple instructions for my old 2.3 had the belt lengths listed in it. Have you reached out to Whipple?

I haven’t yet. Haven’t received the blower or an update on expected ETA from lethal yet. Just bought last week. Trying to get everything ordered and on its way so I can limit the parts orders once I’m in the middle of install.

 

[2003RedfireVert]

Here are my calculations for my KB with a 3.5 pulley. I have a J2Fab alternator. I don’t know the pulley size but these measurements assume stock size pulley and I have zero belt slip or fitment issues. Stock lower pulley as well.

LMR is where I started. If you go down to a 3.25 then I think you remove .5in of length….so when I go down to a 3.25 I’ll be ordering a 78in belt.