i'm sure this has been asked a million times, but i can't find the answer. i understand what it does, but how do you figure out what spring rate is best for your setup?

 

put a vacuum gauge on your manifold, look at the tial spring chart, choose spring that fits what your car has for vacuum at operating temp at idle

don't have a vac gauge? guess what $10 will get you one at harbor freight

http://www.harborfreight.com/fuel-pu...ter-93547.html

 

so the spring should just simply match your vacuum at idle? interesting

 

For spring-specific BOVs like the TiAL you need to go by vacuum

http://www.tialmedia.com/documents/BOVspc.png