TEXT FPO - Driving Sports TV

RALLY LIKE A ROCKSTAR
open class cars and straight-line speed. We knew at
the end of last year that we needed to move on with
development even though we were getting the very
most of a well-prepped car.”
While last year’s car was mostly a Group n car
prepared by Prodrive in the United Kingdom for
european Group n competition, a few modest
specification changes between Rally america open
class cars and Group n give the U.s. cars the power
advantage, most notably the use of a larger 34mm
restrictor, as opposed to the 32mm Group n restrictor.
The team worked with Garrett engineers to
piece together a new turbo, knowing that was necessary
to be competitive with the factory team in
2008. While circuit track cars operate in the 5000-to-
7000rpm range, a rally car mostly sees loads in the
3000-to-5000rpm range, so they needed a turbo that
would give the cars good low-end grunt and not be
gasping at the top end. These turbos also need to be
able to stand up to the rigors and heat of the antilag
system the team runs. The result is a Gt3071 that
has been slightly tweaked to be more responsive at
low engine speeds.
“The Garrett engineers pieced together a turbo
that would be matched to our engine, restrictor and
the stress of stage rally,” said Pinker.
Unlike your road stI, the Rockstar cars have to
be easily serviced in the field, and while it may not
be difficult to pull your own engine in the normal
sense of the word, the Rockstar team needs to be
able to swap a transmission in under 40 minutes.
This means that every part has to be engineered with
serviceability in mind. Initially, when the team contacted
Jeff about mounting the new Garrett turbo,
which is very similar to the unit Perrin uses in their
own rotated kits, the first thought was to just use an
existing Perrin kit. however, it was discovered that
the turbo sits too far back in the engine bay and thus
restricts access to the transmission, making access
to the bell housing impossible without removing
the turbo system. That was unacceptable in a world
where removing too many parts would be the margin
between victory and not starting a stage.
It was then decided that the turbo would be
mounted on top of the factory twin-scroll headers
using an adaptor that would push the turbo and
wastegate forward, and allow the team to use their
slip-fit quick disconnect fittings to allow maximum
access in the engine. The turbo, wastegate and
downpipe can be removed as one piece if need be.
to make things even easier, the team employs
“dry-break” fittings. These are basically quick-disconnect
lines for fluid and oil. When the connection
is broken, a valve in the connector keeps fluid in the
78 July 2008
Left, the new GT3071 used in the Rockstar cars. Right, a standard
GT3076 that Perrin uses in their own rotated turbo kits.
Since Jeff has to make four exact copies of the new turbo setup,
he constructs templates from paper so that he can make exact
copies of each pipe in the manifold.
The finished product with adaptor plate, wastegate, turbine
housing and downpipe welded and bolted into place. Notice the
slip joint on the downpipe.
The turbo kit in mock-up. Notice that Perrin has rotated the compressor
housing to eliminate the Y-pipe making installation easier.
Jeff then used this jig for the actual welding of the turbo setup,
that way each spare turbo kit will be identical.
Jeff Perrin (right) and co-driver Robbie Durrant (left) configure
Alta’s in-house Dyna Pack dynamometer. While the cars may not
make huge amounts of horsepower they do make mountains of
torque.