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Anyone know what a 559-M1 head is? That was added since 1/4, which previously only listed the 2531110M2 alum. Is there another source for steel head castings?

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Matt, the M1 is the "race" casting made by mopar. A little higher cast intake runner, a little less material on the intake face. I'm sure theres more differences that Jeff could elaborate on, BUT- I tried finding a set of castings two years ago, and still haven't found a set...

And as of right now, Mopar is the only source for Iron Heads.

The aluminum head deal with the street hemi is to add 80 lbs. I'm glad I have new iron castings on the shelf.

I just hope as Jay has pointed out, that this is not NHRA's answer to the intake face bs