Head Porting basics

When I port stock heads, I use a 1.94 chevy valve and keep the throat 86% of that.
That allows you to keep a venturi effect in the port. With the right porting, valve job and chamber mods you can easily get high 260's at .500 lift and with alot of work you can get it to flow up to .600 lift and usually 275 or so cfm.
The reason I don't recommend that much porting is stock heads are prone to cracking so it's possibly wasted money.

If you do it yourself, then it's just wasted time if they crack.
I don't have any pics of stock heads I've done, sorry but it's good to enlarge the pushrod pinch as much as possible without making holes and maximizing the chamber size around the valves and a good valve job.