To the right 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
for a stock Subaru block where coolant circulates about the cylinders to keep things cool.
On turbocharged motors
up to about 10lbs of boost it's OK to use a stock block like this. However, with the extra stress of higher boost
levels and running race gas, these cylinders will actually move around with
vibration, enough to quickly wear
the head gasket out. This results in coolant seeping into the cylinders,
evaporating, depleting coolant in the radiator system and eventually your motor will overheat.
If you don't keep an eye on
the temp gauge and radiator level you can easily cause some serious damage to
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.
Small holes are provided 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
to preserve the integrity of the head gasket and overall motor life. Generally speaking if
your run over 10lbs of boost you need a closed deck block to be reliable.