I just got another pair of Vortecs, and was looking into modifying the exhaust side.

While searching around, I came across this at ChevyHiPerformance.com: <BLOCKQUOTE>quote:</font><HR>"...some ¾- and 1-ton trucks came with Vortec heads equipped with a specially hardened exhaust seat that kills low- and mid-lift flow. Casting number 10239906 should be avoided."<HR></BLOCKQUOTE>

Well, it turns out that the heads I got this time are the 9906 castings.

I'm thinking of punching out the exhaust to 1.6". Is this possible with these "special" hardened valve seats in place?

I don't see why it wouldn't be, but I'd like some input anyway. Even if it's possible to get rid of these seats and do a Vizard-style 30-degree seat job.

All the other machine work is already done on these heads (studs, guideplates, guides cut down, dual springs, even a 3-angle valve job).

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My Web Site (http://www.landry-family.com) (updated 01-04-03)

"Long Live Freedom!"

Chad Landry
TC Member #643
ACES Member #4556
'68 El Camino

Chad, may want to move this to the Perf. forum. Think I've seen the guys in there talking about these heads. Also, I thought 906 was one of only 2 vortec castings, are were good??? Do a search-maybe you'll find something good.

Good luck!

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Sid Coleman, 71 Ragtop
TC (Gold) #174, MCC #347,
Aces #5457, N3JHV@bellatlantic.net

Yes, the 9906 and 8062 are the two selections available. The 8062 is the one that GMPP sells at $225 each, assembled. The 9906 is a take-off from the 3/4 and 1 ton trucks. This is the first I've heard about a lack of flow with this casting.

Thanks for the suggestion. I've copied it to the Performance forum. I just thought a machinist might pipe in here in this forum.

CJ,
I have a set of Vortec heads at the shop that we are doing for a customer. They are truck heads and not being used for a performance application. I might be down at the shop this afternoon, if so I will take a look at them and see how big the seats are and if they are big enough to use with 1.60 valves. If not, I am not sure if there is enough "meat" in the casting to install a larger seat. I seem to remember seeing a bulletin about this somewhere. If I have a chance, I will see what I can find out. I have no idea as far as the flow goes. I am pretty sure that the truck heads also used an exhaust valve with a 3/8" stem, so you will have to install new guides for a "normal" 11/32 stem valve.

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

1971 Heavy Chevy - original owner
Team Chevelle #100

Bill, I just looked at the heads closely, and they have the hardened seat inserts on the exhaust side.

Can those hardened inserts be worked to make 'em flow better?

I posted some pics of the exhaust seats and ports at http://www.chevelles.com/forum/Forum4/HTML/013767.html