How far can you port stock heads?

 

E7TE heads, I had a pair that would flow about as well as a set of World Products Windsor Jr. Cast Iron heads. In the end it was a big waste of money. I had them ported (intake/exhaust port to combustion chamber), converted to an adjustable valvetrain and larger valves installed.

Your better off just saving the scratch to get a good set of aftermarket heads. If thats too expensive go looking in the boneyard for a 351 powered Lightning or Early V8 Exploder as both these vehicles were fitted with the much better GT40 heads and save your money by refurbishing them and converting them to an adjustable valvetrain and call it a day. The later GT40p heads are good as well but finding headers to fit them could be problematic.