I have a set of vortec heads with Casting number 10239906. I have read on another website that some ¾- and 1-ton trucks (casting number 10239906) came with a hardened exhaust seat that kills low and mid-lift flow. Should this be a concern or would I be fine using these heads?

No offence, but a "search" will help you out lots here. This particular subject has been done to death.

Nutshell version: don't worry about it - all Vortec heads make tremendous power regardless of the exhaust seat.

My old Vortec combo had the 906 heads with Inconel single-angle (1-ton truck) exhaust seat. From a dead-idle launch I ran a 12.15/110.5 on radials. I don't think it hurt my engines' performance much.

------------------
'Silver Bullet' 1977 Z-28 413" SB
11.73 @ 115.10 on drag radials
Old Vortec combo:
12.15 @ 110.52

The 906 is a hoax. Don't worry aboot it! Both castings work equally well.

[This message has been edited by 1978LT (edited June 11, 2005).]