TEXT FPO - Driving Sports TV

ket specific to the subaru 2.5-liter turbo engine. so
far, it appears that these pistons are a universal fit
for the eJ255 and eJ257 and will not alter the compression
ratio for either as long as you are using a
stock compression piston. We contacted Cosworth,
which sent over a set of its 99.5mm stock bore pistons.
(note: this my be different for 2008 and newer
eJ255 engines so make sure you consult with your
parts supplier before ordering parts.)
If you decide to reuse your old block, again you
have options. normally, a broken ring-land will not
cause too much damage to the cylinder wall. If this
is the case, and the crosshatch marks on the cylinder
wall are in good condition, then you can probably
install a set of forged stock-size pistons. If the bore
is in poor condition then you will have to go to an
overbore piston. Generally speaking, the first overbore
size for the stI is 100mm, although you can
bore further for more displacement. normally, however,
you don’t really want to push it much past this
cylinder size. also, if you are going to overbore, you
will have to split the case and redo your bearings,
which will add to the overall cost of your build.
an additional note. not all eJ257 blocks are created
equally, and there is some variation in bore
sizes. This is inherent in the manufacturing process.
Fortunately, subaru marks the blocks at the factory
so that you can tell a tight block from a loose block.
blocks are marked with either a “b” or an “a” on the
top. This refers to how loose or tight the bores are on
a stock sized piston. “b” means the bore is tighter
and “a” is looser. so a block marked “a b” on the passenger
side means Cylinder 1 is looser and Cylinder
3 is tighter. Ideally for a drop-in piston setup, you
would want to run a block that is marked “b” for all
four cylinders. Looser bores are fine too, but you will
probably have a bit of smoking on startup as oil will
seep past the pistons in a looser bore. Our block was
marked “bb” on both sides of the case, indicating
tighter bores.
In our case, the number 4 piston had fractured
and was the cause of our excessive smoking and
the low compression. happily, the bores were still
in good shape, so this shortblock can be used again
and will find a home in the Dreadnought, with some
slightly used CP forged pistons. Oddly enough, this
case was also marked with “bb” on both case halves,
so again, we should have a reasonably tight engine,
despite not honing this used block.
a final note: Dropping the coin for an engine
build or a built engine can be a serious proposition,
so ask yourself this question: Why am I doing
this, and what are my goals? If you want a 700whp
daily driver/drag car/track car exotic killer, etc., you
may be in for a rough journey as it is very difficult
2007 LEGACY GT PROJECT
Tim Hadfield from F.A.M.E. Automotive in Redmond, Wash.,
listens to the block and checks compression. Our fears were
confirmed: loss of compression on piston #4. (Below)
“Why am I doing this? What are my goals?”
and very expensive to execute this all-arounder effectively.
nor will a built engine be the end of the
road. If you are looking for a streetable fast car that
occasionally sees track time and just needs the extra
insurance that forged internals offer, then your goals
are more rooted in reality. to be sure, all things are
possible, but those possibilities are closely tied to
your budget and expertise.
The following is a guide for building up a fresh
shortblock using forged “drop-in” pistons. hopefully
these hints and tips can help you along if you
do decide to do-it-yourself. In addition to the usual
set of metric wrenches and ratchets, you will need
some specialty tools.
- an engine stand
- an engine hoist (cherry picker)
- Piston ring compressor
- extra long screwdriver (12-inch plus in length)
- Piston ring grinder/gapper
- high-quality torque wrench
- Parts washer or a basin to wash parts in
- Lots of brake cleaner
- Fuji bond (available at the subaru parts counter)
- assembly lube
SubIESpOrt MagazInE 53