EAB heads - rough casting in valve areas?

Jack 34pu

Jack 34pu

Senior Member
I picked up another set of EAB heads at Hershey. They have rough surfaces around the valve areas and over part of the piston. The sand mold used in casting must have been porous. The question is whether to clean and polish that area or leave it rough. It seems that carbon would collect there yet I heard that you want to create turbulence in the combustion chamber. Hopefully some wise old sage will enlighten me.
 
Most of them are relatively smooth in the chamber area. They may have rusted up from sitting out in the weather too long. It definitely won't hurt to polish them smooth again.

Kerby
 
The turbulence during combustion is furnished by the "quench area" (modern term), the tight space between the top of the piston and the shallow domed area. This area effectively closes down to almost nothing as the piston comes up to the firing point, shoving the mixture violently over. Without a tight fit there, the engine lacks said turbulence and becomes more sensitive to knocking under load, among other things.
Remember all the smogger cars of the 70's, clattering up hills?? GM went to an idiot piston design on the SBC, fixed during the '80's, that essentially eliminated quench.
 
To clarify, this is not pitting - it is like little metal particles on the surface. The sand mold must have had tiny voids that filled with metal when cast. Just a rough casting.
 
Yup, take off all the high imperfections, but don't try to get them smooth, if it means grinding out pits.
 
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