I'm thinking of getting a cam and know the basics about the numbers but I am confussed on one point. I figured this was techinical enough for this board so... I'm just a little confused by the LSA (lobe separation angle). example...a stock cam with an intake lobe center line of 117* ATDC and exhuast lobe center line of 122* BTDC should have an LSA of 119.5 (using the (intake+exhaust)/2 equation). Being curious and a visual learner I drew this cam on CAD. The actual angle between the lobe center lines is 121*. Where did the 2.5* go. Or perhaps a better question - Where does the (I+E)/2 formula come from. I feel stupid right now. Another example...Take a came with 128/128 lobe center lines. the distance between them is 104* but the LSA would be 128. I'm getting under my desk and hiding....please help

 

I forgot the cam only makes one revolution and the crank makes two per cycle. Now i get it.

 

interesting example and yeah you can see the confusion... one working in crankshaft degrees and the other (lca) ground into the cam itself.
one thing though, based on the info most grinders provide, you usually end up working with the intake centerline and the lobe center angle then find the exhaust centerline. that's if you want to work towards finding the opening and closing event timing. most don't give an exhaust centerline per se but it is easy enough to calculate.

glad you found your error.

JB