Piston widows.

[bwalker]

One thing that really gets guys tied in knots is fixating on bulk flow, when timing is alot more important.

 

[Al Smith]

They both make about the same on compression. The hemi design has a better burn though.

If I'm not mistaken it has somthing to do with flame propigation as does a cut dome design commonly called a " pop up " .The Stihl 038 AV used a hemi dome but has an off set cylinder to lessen or prevent a short circuit during the transfer blowing part of the charge directly out the exhaust port .