[Litdave]

I have what I thought was a matched set of L31 vortec head (906 casting) that I was going to put on a 383.

I noticted that the exhast seats or different. One head's date code indicated it is a 2000 and it has a exhaust seat insert. The other head is a 1996 and it does not look like it has an insert.

Is this possible? Is there a diffenence in heads between years?

Thanks, Dave

[BOBCRMAN@aol.com]

You will find minor differences not only in years but in the numerous production runs. Minor differences even in the same no. castings. What you see is possibly the seats fully cut at a different height in the casting (common). The seats could have been repaired on the production line (also common).

Have a good three angle valve job done on them, shorten the guide height, blend any sharp edges, smooth the short side port radius and run them.

[jimfulco]

I think some of the -906 heads that were destined for heavy-duty trucks were fitted with exhaust seat inserts by the factory.

[sb72elcamino350]

can you take those bad exhaust seats out?

[Litdave]

The seats aren't bad.

I thought I remembered reading what jimfulco said that some heavy duty trucks had inserts and that they did not flow as well.

Can anybody confirm that all heads with inserts are from heavy duty trucks and do not flow as well as heads without inserts?

[sb72elcamino350]

Can you take out the inserts?

thanks

[jimfulco]

If you take them out, your valves won't have anywhere to seat. If they don't have smooth transitions to the exhaust ports, you might be able to fix them with a grinder.