Centerline
 

Does the centerline have to do with vacuume in the engine? More or less for smother running engine. Every day streetcar. My cam 110 centerline with 240/242 donation.

Not sure I understand. Are you saying that your cam has 110* between lobe centers? Or are you talking about advancing or retarding the cam timing? And is the 240/242 the advertised duration or the valve duration at .050"?

Indirectly, yes.

Idle vacuum is a direct function of valve overlap (the period of time when both intake and exhaust valves are not fully seated). Overlap increases as durations increase and/or as lobe centerlines are brought closer together (i.e: lobe center angle decreases).

Simple explanation which I hope was helpful.

If your cam is hydraulic, 240/242 duration at .050 lift is on the long side for a street cam. It will idle rough and have low idle vacuum even if you advance the cam timing.

Absoutely. The cam in my 383 stroker is 240* at .050" and it does have a rough, lopping idle and about 10-11" of vacuum at idle. But it is advertised at 270* duration. Advertised duration and duration at .050'' are normally very different things, and make a difference in vacuum and engine performance. As will lobe separation, as 65Tripleblack stated.