The "Throw Away 318"

Bret Tschacher said
... At least with the SB's you could swap on a set of 318 heads on a 273 and see a noticeable boost in flow. Of course putting a set of 202 340 heads on a 273 was out...

318 heads are a power loss compared to 273 heads, both in compression and air flow. I've run 1.88 intake J heads on a 273 with good result.