I have never heard of hardened inserts in those heads any picture I have seen of these heads from the factory the are induction hardened. The only way you can "see" the induction hardening is when the are new, the area all around the see is "blued" looking from the heat. Why are you asking????
the 906 casing were made two ways,pressed in and machined seat and induction hardened.
I have read conflicting reports that the pressed in and machined seat disrupt exhaust flow hurting performance. I would like to see the difference between the two with a picture of the exhaust port. If there is a visible difference . I obtained a set of 906 heads and would like to know what to look for.
If it has pressed-in seats, you'll definitely be able to see 'em. The early ones had a terrible valve job, it was practically a 90* angle into the port. The later ones are much better. All the 906's I've seen have pressed-in seats. Don't believe everything you read in the rags, either - most have retracted the statement about hurting flow. Once you've got the bowls cleaned up, short turns worked a bit and whatever chamber work you want, there won't be a nickel's difference between your 906's and the 062's.
Now that is the answer I was looking for.
I also read that any porting would hurt flow.
Now I have done some porting on other engines I have built and it would seem that the same rules would apply to a vortec exhaust port. Smooth curves and no sharp edges would help. Does anyone disagree??
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