mx5cartalk.com

Read this article about power porting/extrude honing of intake manifolds. It involves forcing an abrasive medium through your manifold, resulting in enlarged passageways and the removal of power robbing, roughcast surface contours. The procedure removes and polishes metals only where air flows, an ability that traditional methods of porting can't see - let alone reach. Best results are with forced induction, however, it also helps top end power in n/a engines.
Essentially, improving the airflow allows you to generate more power without adjusting boost, or alternatively, maintaining the same power when running less boost...

http://autospeed.com/cms/A_0622/article.html

And yes, I have a vested interest in you reading this article. I have a power ported NB8B manifold power ported from an unfinished project for sale.

viewtopic.php?f=44&t=33855

i've read that article previously. it's pretty interesting stuff.