BB Mopar "906" Head Rebuild, Costs vrs Flow/Perf Potential

[tan top]

 

[PRH]

What would you think the crack potential is?

They aren't "maxed out", but a lot of metal comes out of the valve seat area when you install the bigger valves and do some bowl cutting.
The two most common areas I see for cracking is externally under the 2 center exhaust ports, and across the intake seats from the chamber down into the bowls.

The more power you make........  The more likely they seem to crack.
The chambers "oil can" and fail where they're thin.
I think the area under the exhaust ports gets brittle from localized thermal cycling, and when your making power, the head is trying to be "lifted off" the block, and sort of pulls the head open in that area.
Ive seen heads that had 2-3" cracks in that area that didnt leak at all until the motor was under power.

So, the porting and larger valves definitely reduce the reliability of the head(IMO), and the heads being milled .050 takes some overall rigidity away from the casting, although I'm not sure if that has a big impact on the cracking under the exhaust.
I haven't done anything to this set of heads that should make them more crack prone than other sets that flow similarly....... And some of those have cracked, while others have lasted years and years.
For the most part, I feel it's just a crap shoot whether they crack or not(unless you have tune-up or cooling system issues).

The way I see it is, if "high reliability" is pretty far up the priority list....... Leave them at std valve size, don't port them all that much, and keep the milling to something reasonable.
Std valve size heads with mild porting(260-270cfm), and 84cc's or so with aftermarket valves would be my suggestion for keeping the reliability(reasonably) high.

I guess we'll just see how these hold up.


Flow at lower lifts:
Lift------I/E
.300---210.7/152.2
.400---244.6/187.8
.450---255.4/199.6
.500---268.5/203.7
.550---275.6/208.3

[aerolith]

 

[C500]

I just remembered, this wonderful 440 engine was removed from a 69 1/2 Sixpack Superbee in the 80's!

Fortunately someone realised and the engine was re-united with her again about ten years back.
When the engine was rebuilt with another block, IT BROKE into many pieces!!!

SP Superbee is now in France...with her original NINE second Rob Loring 'ICE' engine lol...

Aerolite / aerolith... aka 500jon???

[aerolith]

Hi C500,

Yep one and the same!
My computer died and I had password probs so I re-stated again as 'Aerolith'.

As I am a Dodge Dionsaur I needed to match my neolithic heritage, so I found an archaic name for myself,  Aerolith or Aerolite depending on the dictionary used lol...

Meteorite is more modern talk, which I think is apt for my Aero, crusty but very quick!

[aerolith]

Good points there PRH!

I have a good collection of BB iron heads, some ported in the UK and some from the US of A.
I would say the ICE heads were easily the most unique but a set of 452 Koffels I had were pretty trick too!
Yep the flatter ports of the post 906 era heads are easier do, but I ave some 915's that will deffo go into the 300's.
They are 'old-skool' hogged out to the max and have the closed chamber of desirability.
The Koffels were machined to the max and when you picked them up, they felt uncannily light!
Probably machined over 100thou off the mating face and a small quench recess re-machined back in to give 'zero deck pistons' some room to play.
Then I found another pair of luvly 906's on my infamous drag-Charger 'LFN 7', the tops of the runners were welded up just before the valve guide.
Then they were ported to the max not unlike the hogged 915's but much higher around the guide boss.

Now they are all just 'talking points' in the era of Cheapo Chinese aluminum heads.
You can't stop progress, but you don't have to destroy the past, to make way for it...

Aerolith