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Old 02-14-2009, 10:51 AM   #54
67_C-30
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Join Date: Jan 2005
Location: Sweet Home Alabama!
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Re: Heads for a 350 chevy

Quote:
Originally Posted by Skirkpat View Post
Casting number 10239906 should be avoided.
Not true. The is a release from Sallee Chevrolet.

Quote:
Please Note: The casting number myth debunked:
The myth is that there is a difference in the head performance produced by these two castings.This myth was started by some Magazines that didn't do their homework before publishing their articles. This is the truth the whole truth and nothing but the truth. So sayith the Grand Wizard GM and his Apprentice Wizard Sallee Chevrolet.
10239906 casting has one large single hump.
12558062 casting has 3 small humps.
If either of these two castings have not been altered by GM and the part number changed from 12558060 or altered by someone else (previous owner, etc.), the heads produced by either casting will be identical except for the external cosmetic difference. Both castings are used to make the 12558060 Vortec heads which are the true unaltered Vortec heads.
Heads from both castings come out of their cast IDENTICAL except for the minor cosmetic external differences!!!!!!!!
I built 2 limited late model dirt track engines with 906's last year, and one them powered the car to 7 feature wins. Some of the 906's that came on 2500's and 3500 HD's had a hardened exhaust seats installed instead of being flame hardened like the other 906's and 062's, and it is a little smaller than on the 060's and 062's, but on a flowbench the numbers are so minimal that you'd never know it in power production. If someone is still worried about it, a simple bowl blend makes them flow the same. The hardened seat 906 is actually a better head than any of them for racing because the hardened seat was installed because some of the Vortecs were cracking around the valve in extreme use in heavy duty trucks. A Jan '03 article by Chevy Hi-Performance started the "avoid the 906" craze, but it circulated as fact.

BTW, If anyone has any those useless, wretched 906's that they won't use, let me know and I'll PM you my address and shipping money!
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Last edited by 67_C-30; 02-14-2009 at 10:53 AM.
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