Parksr5 is correct. Dave will set them up with whatever spring you need. Mine look and perform great. I must say the only reason am running antique iron 906s on my ride is that the rules dictate that is what I must run. If I could run something else I definitely would. Seems like MM was in the $2500 range when I talked to Eric about them last year fwiw.

$1500 is cheap money for that job.

FWIW, I saw an article in a Mopar magazine about that 906 CNC service, had to be at least 4 years ago. Out of curiosity I called MM for pricing, they told me it was $2200, with customer cores.

Under optimum machining conditions aluminum removal rates would be much higher than cast iron, but the porting cutters and even the CNC porting machines capabilities can be factors in maximum cutting feed rates as much as the material being machined.

Three dimensional contouring of a port or something similar necessitates constant changes in directions. The ability of a CNC machine to process the code and the ability of the machines axis motors, software and hardware to accurately follow the programed tool paths often limit the highest practical feed rate, rather than the material being cut. The moving parts on the CNCs can only accelerate so fast in a short distance, and with the need to slow down for corners, then accelerate again, and slow down again feed rates are limited. So what is doable for actual feed rates for longer straight or gently curved paths is not obtainable for this type of machining. One way to visualize this is CNC tool paths are a lot like race tracks, short straight stretches with tight corners slow things down, even if the car could theoretically go faster.

On factory iron heads I doubt depth of cut is very deep over the majority of the port surface which would further speed things up and the feed rates probably can be run closer to aluminum than one might imagine.

Thanks for clearing that up Mike!!

Sounds like you're saying it probably doesn't take much, if any, more time to CNC an iron head over an aluminum head.

Wow I bet the customer could FEEL the difference on that swap!
That might pick up 1 second?
I used the templates on some 906s on my Super Bee. HMMMMM they might still be on that 440, 10:1 slightly bigger than stock cam (.468")? headers and six pack 12.18 with slicks 3780 #s with me in it.
Don

That's my best guess. I'm not not sure how many tons of metal we have cut with out CNCs, hundreds I would guess. I haven't done any full CNC head porting, but it's similar enough to other 3D surfacing like molds and stuff that I think my estimate is probably correct.

One think I know for certain is I hate machining cast iron, it makes a nasty mess, it's a lot like dirt or mud when you do a lot of it and the coolant washes it around in the machines. If you cut it dry then its like dusty dirt.