I'm almost embarrassed for asking this question, but how do closed chamber heads differ from stock or open chamber heads???

 

If your looking down at the combustion chamber on the open chamber head the combustion chamber will be almost the size and shape of the cylinder. Open chamber heads typically have a much larger combustion chamber volume and will create less compression.

A closed chamber head typically has a smaller combustion chamber volume due to the fact that the shape is not usually round, its either an oval shape or heart shape. This lower volume will typically creat a higher combustion chamber. Imagine taking an open chamber head and welding half of the chamber up and resurfacing the head to make it flat.

Both designs have different flame travel characteristics. If you have a flat top piston imagine it coming to Top Dead Center and almost touching the head where the combustion chamber is flat. The area of the combustion chamber where the piston and the chamber flat is called the quench area. Typically the more quench area the less prone to detonation. Theoretically if you have two identical engines with same compression ratios, but one has open chamber heads and the other has closed chamber heads, you will be able to make a little more power with the closed chamber heads because you can run more spark timing advance without detonation.

Please note: "typically" and "theoretically" is used alot in this explanation. I realize that these principles in engine building don't hold true in every single case, however they are a pretty good rule of thumb. I just don't want to start an arguement.

Hope you understand my explanation.

 

It all makes sense to me now. I've seen closed chamber heads, but I never knew that's what that type of heads were called.

Thanks for the explanation.
SS