Any GM SBC Guru's here?? Vortec head question.

[mrpyle]

So ... as the title suggests ...

I was looking at buying a '99 long block assembly. Low miles, pulled from a Tahoe. Roller cam/lifters ... all stock.

Block number 10243880 .... Vortec heads.

Here's the dilemma ... left side head - 12558062 and right side head 10239906. The 906 being the one most enthusiasts would steer away from.

Now the question .... why would there be mismatched castings?? Since I'm no expert on the matter, I'm hoping someone here might know.

The seller claims that some of them came like that, from the factory. Which doesn't make sense to me. Especially since the 906 doesn't flow as well as the 062, why would the manufacturer put mismatched heads on? My first thought was, someone replaced a head. For whatever reason. The seller bought the vehicle used, so he had no idea of it's previous misfortunes.

Anyway ... I'm sure someone here can clarify if and why GM might do that. Not that I think they would. But maybe this is normal pratice? Hence ... why I am asking.

My only other question is ... of the 10243880 blocks ... some have the coolant bypass hole on the right side and some do not. Why is that?

[shank0668]

Originally Posted by mrpyle

So ... as the title suggests ...

I was looking at buying a '99 long block assembly. Low miles, pulled from a Tahoe. Roller cam/lifters ... all stock.

Block number 10243880 .... Vortec heads.

Here's the dilemma ... left side head - 12558062 and right side head 10239906. The 906 being the one most enthusiasts would steer away from.

Now the question .... why would there be mismatched castings?? Since I'm no expert on the matter, I'm hoping someone here might know.

The seller claims that some of them came like that, from the factory. Which doesn't make sense to me. Especially since the 906 doesn't flow as well as the 062, why would the manufacturer put mismatched heads on? My first thought was, someone replaced a head. For whatever reason. The seller bought the vehicle used, so he had no idea of it's previous misfortunes.

Anyway ... I'm sure someone here can clarify if and why GM might do that. Not that I think they would. But maybe this is normal pratice? Hence ... why I am asking.

My only other question is ... of the 10243880 blocks ... some have the coolant bypass hole on the right side and some do not. Why is that?

Definitely would not have mismatched heads. Common sense would lead me to believe that having a different head would not make a v8 run nearly as smooth/efficiently as it should.