Vortec heads were used only on turcks and starting in 1996. It is confusing because the word "Vortec" is a Chevy engine name like the "Blue Flame" and "Turbo Fire" engines of old. The engines for years immediately prior to 96 were also called Vortec but were not the high flow heads and central point injection that we know as Vortec. The LS style motors replaced the Vortec stuff in 2000 or 2001 depending upon the model of truck.

Here is a link to info on the heads:

http://www.sallee-chevrolet.com/frame.html?/start.html

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