I made this statement earlier in this post. It may be incorrect. I have an AFR head and a ProMaxx (Steven Sun) side by side. I do not think they come from the same foundry. It appears that the AFR is a copy of the ProMaxx but could be made elsewhere. There are color and texture differences in the castings, differences in machining methods and a little bit of difference in sizes and shapes of certain areas.
The metal color and texture on the AFR head look like the Speedmaster. But Speedmaster uses helicoils in the exhaust bolt holes and in the rocker shaft bolt holes. The AFR has neither. The AFR and the ProMaxx have 6 angles from throat to chamber. The Speedmaster has 4. The AFR has a CNC throat blend. The Speedmaster has nothing and the ProMaxx is a hand blend.
So this could mean a third Chinese factory making SBM heads?
AFR on the left, ProMaxx on the right. Blue arrows indicate some differences.
And one more difference. The rocker shaft fits in the saddle of the AFR head nicely without wobble. Speedmaster apparently has trouble making that happen.
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