If you take a clear look to the Novarossi onroad engines and how they perform then you have from low price up to the most expensive:
- 3 port basic -> slow
- 5 port basic -> a bit faster
- 7 port basic -> looks like something
- 7 ports competition -> competive
- 9 ports -> for most the one to have
- 9 ports tuned -> a screamer
Most people do only compare these engines on a track and see the differences and choose their options within their price range and mostly the basic line falls off.
Once I did fit a basic 3-port P/S set into the housing of an old NovaMega EVO5 competition engine. Not much modification was needed, the intakes were as good as the same but only the exhaust was raised and widened to look more like the original EVO5 exhaust and some teardrops on the intakes were made.
The engine did run very good after testing some exhausts and did even outperform a Mega ZX21-R DS2. The guy running the ZX21 did not believe it was a 3-port engine so I did take off the head and showed him, he was stunned.
The picture most people have about the ports is only made by how the manufacturers show us their products. The real big differences between those engines are how they are configured with the timings of ports and crankshaft.
The only problem you can face by tunning up a low performance engine up to a competive engine is the lifespan and strength of the materials, the rod and piston are mostly made from cheaper and less strength materials as also the crank is less hardened. For a part this is also making the differences in the prices, not only the materials but also the production costs