It all depends on how you have the engine built. Doing just porting does not mandate you running race gasoline. High-octane race fuel is required when you have certain types of head work done (milling, squish-band alterations, re-chambering) that increases the engine's compression ratio. Generally, a compression ratio greater than 10.5:1 requires the use of high-octane race gas in that engine.
Wildcard 2 and the other techs can probably explain it in more detail (or correct me), if needed.