i have been hearing that 190 cc is the best for naturally aspirated engines. but would it be bad to go with 200..or 180 even?..does any allignment get mest up if not 190?

 

89,

There are a few more variables involved. The optimum port volume depends on the valve size, cylinder displacement, intended engine RPM for peak power, valve lifts, port shape, intact tract length, and probably some others that I'm not thinking of.

Saying that 190cc is best for an NA street engine is just too broad a statemetn to be accurate. 190cc would be way too big for a 305CI truck engine, and way too small for even a mild 454 or 505 low compression engine. The port volume has an effect on port flow velocities, which is probably the more important consideration.

And don't presume that the port volume has a lot to do with port alignment. Two completely different head designs can have the same port volumes and act completely differently. 23° heads with large ports would probably flow less than an 18° head with the same port volume. Splayed valve or high port heads change the alignment and flow again. Consider all the variables before deciding what is best for your application. As always, bigger isn't always better, and there is a lot of homework to be done to get the best result.