dm, I found this at
http://www.s10extremist.org/tech_articles/vortec.htm
The Vortec name first appeared on 4.3L V-6 engines in 1986.These engines were the first to use a new "Vortex technology" designed to create a vortex (powerful swirl like a tornado) inside the combustion chamber. The Idea behind this is to create a more even and well mixed air/fuel charge that both generates more power and is more efficient. Over the years this Vortex technology has changed and improved to develop many new changes in the GM power train division. In today's world 'Vortec' Means power and here is where the confusion starts. There are literally thousands of cylinder heads that have been made with the vortex technology since 86 and many people refer to 87 and later small block heads as 'Vortec' heads. While this is a half truth the heads that GM sells under the Vortec name and the ones everybody is buzzing about did not exist until 1996. From the exhaust side of the head you can't tell a vortec from any other head. They look nearly identical to all other chevy heads. The ends also look more or less the same. All the accessory holes on the outer edges look just like any other 87 and newer center bolt head.
The intake bolt patter is different! It uses an 8 bolt attachment. This unique bolt pattern and the casting numbers are the quickest way to tell them apart from other heads. You also can tell by the casting mark on the end of the head since the vortec head has a 3 triangle or 'sawtooth' casting mark. They are available under 2 casting numbers 10239906 and 12558062. Both casting are good and performance wise they have no difference.
Good web site, and lots of info.
