What does one mean when they say "open/semi-closed deck" as compared to a "closed deck" when talking about engine configurations?

 

Look at the top of an engine block from a Honda engine. When you look at it you can see the water passages for the cooling jackets around the cylinders, as such it uses the head to cap off the water jacket. When you look at say the 4G63 or a small or big block chevy you cannot see the water passages thus they are closed deck engines. This is why when you get to the major hp levels in Honda engines you have to add an upper girdle for support, otherwise the cylinders will go out-of-round.

 

Open decked blocks have cylinder sleeves in which the pistons ride (usually Al block). They can be seperate entities from the block. Semi-open deck, like on the STi, has "supports" that extend from the sleeve to the block (usually Al block). Closed deck, most iron block motors like the 4G63, 1.8T, etc have this design. Here the cylinders are simply bored out of solid iron at a slight expense to cooling, but the extra strength is more than worth it in my book


Open deck Subaru design (WRX, etc)


Subaru block modified to become closed deck...



I can't find a pic at this moment of the semi-open deck, but just picture the open deck with sleeves that have a coulpe of supports that run from the sleeve to the block to help strengthen it.

Edit: Here's a semi-closed block from the STi..

 

http://www.legacycentral.org/library/deck.htm