ok so in all my reading it seems the 906 vortecs are not nearly as good as the 062 but people seem to use them frequently..... is the exhaust seat restriction somethin easily removed at a shop or are people just not wanting to scour for the 062 castings?

 

Ajmaudio: Here is a writeup from Gilbert Chevrolet: Inserted by GILBERT CHEVROLET
There is no difference between either of the Vortec head (P/N 12558060) castings except for a couple of minor external cosmetic details. The two casting numbers are 10239906 and 12558062. GM has and does take some of the P/N 12558060 heads made from either of these castings and makes alterations to them to better fit specific applications. When GM does this, they change the part number of the head. Buying Vortec heads used is risky unless you know what vehicle they came out of, what part number the head is, and what modifications where made to the head to make it that part number. You can not go by the casting number, as suggested by this article, you have to go by the part number of the head when buying used Vortec heads.

Also: Inserted by GILBERT CHEVROLET
The GILBERT CHEVROLET solution is to use Crane Cam’s 10309-1 drop-in valve spring and retainer kit which is good for .550” lift with no machining.
The installed height for this Crane Cams kit is taller and the lower part of the retainer is shorter.
The “AVERAGE” clearance between the retainer and seal is .575” for this kit.
We have found that some of the Vortec heads, coming from the factory, do not have the valve seals driven on all the way. You need to check that they are before installing this kit. If they need to be driven on all the way, we have found that a 3/8” drive - 1/2” socket fits the valve seal just about perfect.
As with all modifications to performance engines though, you should always measure to assure that there is proper clearance and fit.