Here you see a stock 2.5 liter Subaru EJ25 block before our special work
has been performed to close the deck. What's a closed deck?Notice all the open space around the cylinders, this is the water jacket
of a stock Subaru block where coolant circulates about the cylinders to keep things cool. For turbo motors
up to about 10lbs of boost this is OK, but with the extra stress of higher boost
levels and running race gas, these cylinders will actually move around enough to wear
the head gasket out. This results in coolant seeping into the cylinders,
evaporating and eventually your motor will overheat if you don't keep an eye on
the radiator level.
The picture below shows our modified EJ25 block with our
machine work to fill in the open space and brace the top of the cylinder. We
still leave holes in the appropriate place for coolant to flow through the
heads, but the majority of the space is now filled with billet aluminum using a
special zero tolerance fit. This filler prevents the cylinders from moving
around, or vibrating. This protects against head gasket wear, resulting in
a blown headgasket as seen on
other turbo Subaru motors that are not properly built. Generally speaking if
your run over 10lbs of boost you need a closed deck block to be reliable.
