I picked up some speed master heads on black Friday I plan to put on my 455, replacing C heads, I would like to get them milled down to have 69cc chambers, how much should I tell my machinist to take off? They come 77cc as cast.
also are their any other modifications to these heads you can recommend?
it's a street driven car, shooting for 10:1, comp 292h cam: 292/292 244/244 518/518 on 110.

 

Get ahold of Mark Remmel (cutlassefi) on here. He builds complete engines, and has a complete CNC program for the Speedmaster heads.

 

I'm sure Mark will chime in. I believe they are actually 81-83cc as cast. I believe 1cc is a .006" cut on an Olds head. That means a .072 to .084", so a lot. They also need port work to even flow as much as Gen 1 Edelbrock heads.

 

And if you mill them that much you will definitely either have to cut your intake manifold or the intake side of the heads.

 

As you can all see, out of the box they’re not any better than a good set of C, E or almost any other big block iron head. Chambers are normally 81-83cc as cast, they were never 77 as advertised. To get them to 69 you’ll need to take about .070-.075 off. And yes as mentioned, you’ll need to cut the intake to match. I wouldn’t cut the intake side of the head that much though as it’ll make the valve cover rail kinda thin.
I offer various stages of porting as well if you’re interested.
Thanks.

 

awesome thank you! I saw your post about the cnc porting, very nice!

 

Old Joe Mondello formula. That worked out real close for Intake milling on my first build. Was a SBO with 7a heads and 7111 manifold.

Amount cut from Cylinder Head X 1.3 = Intake Manifold Cut.

His example .050 milled from Cylinder Head X 1.3 = .065 to mill from Intake Manifold

You would need to be sure the heads have not been mill before. For this to work.