We all know that turbocharged Subarus can go fast. Bloody fast. But what you
seldom hear about are the downsides - the annoying traits of the Subie flat-four
that have owners tearing their hair out.
An abysmal lack of bottom-end torque, snatchy light-throttle characteristics
and a temperamental clutch/gearbox combo are the biggest sufferances for
owners.
Well, what if you can have all the Subie speed you can handle without any
drawbacks? It might seem too good to be true, but that’s exactly what MRT
Performance has achieved with their power-up kits for the MY04 Forester XT 2.5
turbo - awesome speed with no downside.
MRT offers three power-up levels for the Forester XT - the XA, XB and XC kit.
We’ll detail each kit shortly but, for now, let’s focus on driving the top-line
upgrade - the XC kit.
Driving the MRT’s Forester XC Kit
At the wheel of a XC-kitted Forester XT, we were gob-smacked by
the constant availability of torque. And we don’t mean just a bit of torque - we
mean push-your-head-against-the-restraint type torque! From around 2000 rpm to
6000 rpm (500 rpm shy of redline), the XC-kitted Forester is a real weapon.
Forget down-changing to get around a dearth of bottom-end torque - this thing
goes no matter what gear you’re in.
The XC kit also delivers noticeably improved throttle response (the Forester
XT uses factory electronic throttle control), starting remains as standard, and
the idle is factory-smooth. Interestingly, MRT reduces idle speed by about 100
rpm to maintain smoothness after the mechanical hardware is fitted; there are no
problems with stalling.
Our one and only gripe is the considerable amount of induction noise from the
revised air intake set-up (which replaces the factory airbox). At moderate
acceleration, the turbo can be clearly heard spooling and it makes various
irritating whooshing noises in other conditions. On the other hand, the high-flow
exhaust provides a define flat-four beat without being obtrusive.
Now let’s talk numbers.
The 2.5 litre Forester XT is already a pretty torquey bit of gear with a
claimed 320Nm peak at 3600 rpm. On MRT’s 4WD Dynapack dyno, this equates to about
1200Nm at the hubs. But whack on a MRT XC kit, and you can revel in 1700Nm at the
hubs at just 3300 rpm - a 42 percent peak torque gain achieved 300 rpm earlier
in the rev range! This graph shows the ‘before’ and ‘after’ torque curves in
blue. Note that the biggest percentage torque increase is achieved in the
bottom-end – up to 65 percent!
The Forester XT’s factory power figure of 155kW (at 5600 rpm) equates to
around 132kW on the MRT hub dyno. Once XC-kitted, output rockets to 205kW at the
hubs - a 55 percent improvement at the same revs! The comparative power curves
are shown in blue in the above graph.
So what sort of straight-line performance come from these monumental torque
and power gains?
Well, with a relatively small amount of stall applied off the line in an auto Forester, the car spins its front tyres on the way to posting a 0 - 100 km/h time
of 5.7 seconds. Read that again – a 5.7 seconds 0 - 100 without effort. No gearbox-destroying launches or slam-changing - just give it a bit of
stall, floor it and watch everyone else fall back in your mirrors!
It couldn’t be easier.
About now you’re probably wondering about the modifications involved in the
MRT XC kit and how much it costs. So let’s get into it...
MRT XC Kit Modification
The top-line XC kit, as tested, comprises six elements - a replacement
exhaust, fuel pump and turbocharger, a cat-less up-pipe, pod air filter and
remapped factory ECU.
MRT’s upgrade exhaust is a full-length 3 inch system with a dump pipe
splitter, high-flow cat converter, centre resonator and custom rear muffler. The
system’s stainless steel construction helps ensure maximum visual appeal and
longevity.
The XC upgrade also includes cat-less up-pipe which is installed prior to the
turbocharger. The Forester XT (like some recent WRX models) is factory fitted
with an up-pipe containing a pre-turbine catalytic converter. This cat is known
to fail under duress – the MRT cat-less replacement pipe improves reliability
and exhaust flow.
At high power levels MRT says the Forester’s factory airbox causes a
noticeable power loss, so MRT replaces it with a polished aluminium induction
pipe leading to a pod filter mounted inside the guard cavity. An aluminium
airflow meter body is also required for the conversion (see pic). This
configuration ensures cold air induction with minimal restriction. Note that the
factory pre-airbox resonator is also removed from inside the inner guard.
For the top-line XC upgrade, the standard Forester XT turbocharger must be
replaced. The small TD04 factory turbocharger is removed to make way for a brand
new IHI VF34 roller-bearing unit which gives greater top-end potential with only
a small driveability trade-off. One MRT technician told us it gives the same
sort of drivability characteristics you’d expect if the factory produced a 200+
kilowatt Forester - strong bottom and mid-range with a slight drop-off in the
top-end.
With the 2.5 litre turbo engine breathing efficiently, the fuel system must
also be upgraded. A replacement ‘500hp’ pump is fitted inside the
tank. The rails, regulator and injectrors remain standard.
The final step in all MRT Forester kits is a remap of the factory ECU using
EcuTeK programming software. Air-fuel mixtures, cam timing, ignition timing and
tumble-generator valve control are tailored to suit and boost pressure is lifted
from 11 to around 15-16 psi. The standard intercooler remains in service.
Given these mods, you can expect your Forester XT to pick up at least 70kW at
the hubs along with a simply stunning increase in torque across the rev range.
And the cost? Well, MRT charges AUD$6490 including fitment and GST. That’s an
attractive deal considering you get a brand new turbocharger and a 12 month
parts warranty – not to mention a whole lot of on-road performance...
Combine the cost of a new Forester XT (AUD$39,490+) and MRT’s XC upgrade
(AUD$6490) and you’ve got a machine that’ll run alongside an Impreza STi for
under 50k.
This XC kitted Forester XT is a vehicle we would gladly own. Tame the
induction noise and it would be absolutely spot-on.
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MRT XA and XB Kits
If you don’t want to go to the extent of the XC upgrade, MRT Performance
offers the entry-level XA and intermediate XB kits for the Forester XT.
The XA upgrade involves merely tweaking the original package. The rear
muffler is replaced with a 3 incher (the same as used in the XC kit), the
factory air intake resonator is removed, a drop-in foam air filter is installed
and the ECU is remapped using EcuTeK software. Boost pressure is increased by
just 0.5 psi (to 11.5 psi).
The XA kit adds a minimum of 15kW at the hubs with up to 45 percent more
torque. The fitted and GST-inclusive price is just AUD$2290.
The intermediate level XB kit is attractive because it delivers maximum
performance without the expense of a turbocharger upgrade.
The XB kit includes everything you get in the base kit except you get a
full-length 3-inch exhaust and pod filter induction set-up (as used in the XC
kit). The ECU is also mapped a bit more aggressively and boost pressure
increases to 13 psi.
Interestingly, the XB kit gives almost the same mid-range torque figure as
the top-line kit but the top-end is held back by the turbocharger - power maxes
out with about 35kW extra at the hubs. The cost is AUD$3990 including fitment
and GST.
We drove a Forester XT (a 5 speed manual version) with MRT’s XB kit and,
although it didn’t provide the top-end thrill of the XC, it delivered awesome
response and immediate grunt. Your head gets pinned back even when you
short-shift at around 3500 rpm...
It’s a real bottom-end/mid-range torque monster.
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Contact:
MRT XA and XB Kits
MRT Performance +61 2 9809 2110
www.MRTrally.com.au
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