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My question earier was missed understood. What I wanted too know was what is the differance , between opened and closeds heads? was the closed chamber heads for hi po motors? when I looked up the conbustion chamber it was 58. something , it did not tell if it was open or closed. did they come closed on all D2OE heads (closed)? I know Z means mustang but what the is (O) standfore?

thanks,
chris
 

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Here's a pic bottom head is closed chamber, I think I'll 302W heads are closed chamber, some have bigger chambers then other though.

http://www.boss351.org/images/btmhead.jpg
 

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open chambers mean the combustion chamber is basically the diameter of the cylinder bore and has a significantly larger volume per chamber

closed chambers have a chamber that is usually a little larger in perimeter than the valve seats. The rest of the head area in the cylinder is a flat roof.

closed chambers can be more efficient because that flat area lends to more controlled combustion (as opposed to using a domed piston in an open chamber head......the flat area in closed chambered heads (known as the "quench") contributes to higher comression without causing slower, less controlled combustion like many "pop-up" (domed) pistons do.....the domes tend to make the flame front "irregular" and are usually more likely to cause detonation than a quench area.

BTW, from what I've read, compression doesnt make but a few percent power difference with modern cams....back in the day when manufacturers didnt know as much about cams, high "static" compression did more for a strong, broad powerband........now days, carefully designed cams allow more power than back then AND use lower octane gas....

I'll stick with about 9:1 (unless I build a supercharged engine....then I'll go with 7:1)
 
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