I just bought a used pulley. It was sold as a 9 psi pulley. How do I measure it? From outer most point all around it is 3 11/16". I guess the inner point where the belt would sit should be about 3.5".

Also anyone have a belt size and part #?

 

Inner diameter is what counts. This thread should help:

https://www.s2ki.com/forums/index.php?showtopic=254159

 

This link as some good info...

 

i am making 11psi with a 3.875 pulley(at 9200rpms) so it all depends on the car, i bought the 3.875 wanting 8-9psi, but i guess my car is just special

 

all depends on Weather conditions and if the Belt is tight...

 

Thanks guys just what Im looking for.