How good are 'typical' cylinder heads from the factory?

[MC Bodge]

How well do typical modern petrol or diesel cylinder heads from VAG, Ford, GM etc. flow air? I know that there were often large improvements to be gained from 'porting' standard cylinder heads in the past, but is this still the case with improvements in production methods?

Nowadays it seems common to take a turbocharged engine and increase output by increasing the air flow forcibly to rather than following the (expensive) traditional route of porting, polishing and fitting bigger valves until later in the process.

ps. I'm not intending to attempt a home porting job.

[MC Bodge]

Thanks for the posts, chaps.

That's interesting about the differences between the Evo and the Impreza.

Edited by MC Bodge on Sunday 20th March 14:01