A so called 318 port was basically designed for a 273 an engine that's 45 cubes smaller and that head is not really designed to make any real amount of hp with any displacement.
That's funny a lot of local guys run 11's with less cubes (308 CI) with a head of similar size in street cars.
As a matter of fact some one will sell you an engine (308 CI) with a mild cam and stock valves sizes similar to a 273 that will run 11's.
These engines are designed for the budget minded who are looking for a low maintenance efficient engine that they can use in their everyday driver, but still drive to the track and run a mid to high 11 second ΒΌ @ 112-115mph with 3,000 rpm convertor and 3.5 gearing.