906 Vortec heads and old school tunnel-ram

[swampratt]

Looks like I am going to attempt some of the hard to mate up stuff soon.
I will be mocking up a 350 with 1996 Vortec heads with 906 casting numbers and Use an old tunnel-ram intake and see how far off the port alignment is.
If it covers the upper part of the runners with the 1205 gasket i think I can modify the intake face bolt pattern on the heads and snug it all up.

But first up is porting and flowing those 906 heads.
This will be a mildish build.
I have never dealt with those newer heads and I am curious as to how it will turn out.
If it even does.

The reason I never ran the vortecs is just this issue I like tall tunnel-rams and those are not made for these heads.

But I was at pull-a-part today which I thought i would be there for maybe 2 hours max getting some 2.5" and 3" tail pipes..Seems all the big tail pipes have been taken.
But i found some really nice looking Vortecs.
I took one all the way apart and no visible cracks after cleaning it up.
I will lap the valves and inspect seats for cracks there tomorrow.

That lapping will uncover stuff that is hidden sometimes.

Fun stuff.
I did some clearance measuring and found some interesting things that I have not read about on these 906 heads.

 

[Snake]

Seems most vortec heads I have seen are cracked in one way or another. Good luck.

 

[swampratt]

I may have got lucky I have seen no cracks yet ...Knock on wood.

So i spent 1 hour and 35 minutes porting them.
I blended the bowls and reduced the exhaust guide boss diameter and raised the roof on the exhaust port .100"
I could go much more.. but that will help a tick.
I roughed up the intake runners where I blended them.
and smoothed the exhaust port.

No chamber stuff and I did not mess with the entry of the intake runner and nothing inside the intake runner.
Just bowl work.
I will take the sharp edge off the chamber edge though.

I did order a vortec intake.
I may just replace the heads on my 57 and it runs a single 4 barrel.
Be nice too see a back to back vs ported 305 heads.

I found out the retainer to guide seal clearance falls in at .470"-.480" My cam is .454".
But if I replace the factory seals with viton 35-305V16 seals which I have on hand I am rewarded with .520" clearance before the retainer hits the top of the seal.

I also have different retainers that add another .040".
Not that I need it.

Now I did not know the exhaust runner floor was raised in these Heads The runner floor at the exit is .250" raised
The top of the runner is in the same location as the older heads.

Yea the exhaust side flows the same as all smogger gm exhaust ports..BUT by raising the floor in the head and leaving the exhaust runner on the exhaust manifold large you get a huge anti reversion deal happening at the exhaust port.. which will actually make that exhaust more efficient than what the "Flow" numbers lead you to believe.


Oldsmobile manifolds were larger than the ex runner in the head.
And i always ported my manifolds or headers to mimic that anti reversion step.

I never tested it back to back but it makes me sleep better at night.