Exhaust - Centre exhaust pipe from a 99/00 WRX
The exhaust on the Forester is comprised of 4 components typically adjoined in this order:-
1) The ‘Up’ pipe – which goes from the exhaust manifold (that comes off the cylinders)
to the turbo charger.
2) The ‘Down’ or engine pipe – which goes from the turbo back down to the underside of
the car and contains the Catalytic Converter.
3) The ‘Centre’ pipe – this joins onto the down pipe and is in the centre underneath the
car.
4) The ‘Muffler’ or diff-back section - this is the last section of the exhaust and joins to
the Centre pipe and ends in the tail pipe which protrudes from the rear of the vehicle.
It’s useful to know about the different components and where they sit when you are trying to
work out what is required for your car, and it also helps when you are talking with other
people or receiving their advice - particularly suppliers!
The diagram below illustrates the Forester and WRX exhaust system. The terms mid-pipe
and centre pipe are interchangeable for the centre exhaust pipe, as is axle-back and diff back
when used to describe the rear section of the exhaust containing the muffler.
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The term Cat-back is used to describe the section of the exhaust that includes the centre pipe
as well as the rear muffler – ie. from the primary Catalytic Converter in the down pipe back.
One of the best ways to improve the performance of any car is to free up the restrictive
factory exhaust. This works particularly well on the early model Foresters as they have an
ECU that is more responsive to changes in exhaust (and air intake) than the 01-on Foresters.
With the later models you really need to adjust the fuel mixtures via the ECU as well, or else
you may even decrease the performance because the car will run overly rich.
The stock Forester (at least the early ones – 98,99,pre 11/00 as I
have confirmed) have a restrictor built into the centre exhaust
pipe, contained within what looks to be a Catalytic Converter. In
fact, the ‘cat’ is all but an empty shell on these models - with a 20
cent coin sized conical restrictor inside it. As the 99/00 WRX
shares the same size and shape centre exhaust pipe section as
the Forester GT, it’s a simple matter to replace the Forester’s
centre with the WRX one.
The benefit of doing this is that the WRX one does not have this centre restrictor in it,
although it does have a real catalytic converter in there (there are 2 cats on a WRX, one in
the down pipe and one in the centre pipe). Whether or not the WRX centre pipe actually flows
better than the Forester has not been proven, but it looks as though it should. It depends on
how restrictive that Catalytic Converter actually is. The fact that it comes from a WRX that has
a higher output from the factory suggests that it is less restrictive though.
The good thing about doing this replacement really comes if you take it one step further –
remove the catalytic converter from the WRX exhaust (any exhaust shop should be able to do
this), and then bolt it up to the Forester. That way, you have an original looking exhaust,
minus restrictor and minus the cat, and still have the Forester’s original centre pipe
untouched, ready to go back on the car if you ever want to revert back to the original
specifications.
If you do remove the cat from the WRX pipe, when it comes to re-programming the ECU
using ECUTeK, you will need an ECUTeK Type 1.5 as a minimum. This is because this
modification will change how the car comes on boost. If you are using a stock Forester centre
pipe Type 1 is fine.
Gear Shift - KartBoy short shifter
Something that is often over looked when enhancing a WRX or GT is the gear shift action – it
is typically sloppy and the shifter is designed as a long throw and easy to shift item by the
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factory designers. A much improved, short (30-40% less throw) and notchy action is
achievable with an aftermarket short shifter installed.
These are available from several manufacturers but most seem to produce items specific for
the WRX. The problem with these shifters is that they are usually 2 inches shorter in shaft
length than the Forester’s one - which means that it just doesn’t suit the higher seating
position in the Forester.
Luckily, due to demand from the US Forester XT owners,
KartBoy has produced a shifter specific for the Forester XT
(KB-001-XT) that also fits the GT here in Australia perfectly.
These are approximately 1cm shorter in shaft length than the
stock one, so maintain the height at which the gear knob sits
relative to your elbow height. I’m really impressed with the way
mine works in the GT.
There will be a marginal amount more noise transmitted to the cabin
because the KartBoy shifter does not have the rubber cushioning in
the shaft that the Subaru one does, but really this is barely
noticeable and the advantages of the short shift far outweigh the
small increase in NVH.
KartBoy also make shifter bushings that replace the factory ones
where the shifter mechanism mounts to the gearbox under the car,
but these make only a very small improvement in shift action relative
to the amount of noise transmitted to the cabin with them in place.
You can certainly hear the gearbox whine more loudly. I fitted them
and then took them off my car again, due to the extra cabin noise.
The KartBoy shifters are easy to install with a couple of tools, and the shorter, less sloppy
shift action certainly makes changing gears much nicer. Highly recommended! These are
available from
www.kastleskorner.com via airfreight from the USA.
Stage 2
Summary
• Suspension - Heavy duty sway bar links and mounts
• Exhaust – MRT 3 inch cat back system
• ECU – ECUTeK version 1.5
• Blow Off Valve – Boost control disabled
• Brakes – DBA slotted rotors, Formula Ferodo pads and MRT brake bracket
• Air Intake – Cold air intake duct
• Gauges – Auto Meter boost gauge
Suspension – Heavy duty sway bar links and mounts
Fitting heavy duty sway bar links to replace the flimsy stock plastic
items, and also heavy duty sway bar mounts on the rear of the
Forester further enhance the on-road handling at the expense of a
marginal amount of off-road wheel travel.
The sway bar links serve to make the action of the sway bar more
linear, as with the plastic links, upon cornering, you experience two
rates of sway reduction. The first is the rate of the plastic link’s
elasticity, and the second the action of the steel sway bar. By
stiffening up the link point, the rate of the sway bar is the one now
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acting to reduce body roll. This provides a more direct and positive feel on the road when
cornering.
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The heavy duty sway bar mounts are what holds the bar to the rear chassis, and there have
been reports of these failing under high cornering loads. I replaced these just because I
thought it was good insurance, especially as the sway bar can be subjected to all sorts of
forces when driving off-road over uneven surfaces.
With the increase in Power that Stage 2 brought to my car, improving the handling was
important to enhance its control. This addition has been a very worthwhile investment in my
mind at only $300 and would be good even on a stock Forester with no other modifications
except a heavier sway bar on the rear.
Exhaust – MRT 3 inch cat back system
At Stage 2, I replaced the stock centre pipe and rear muffler with an MRT 3 inch stainless
steel exhaust. This is commonly known as a ‘cat back’ system because it goes from the
catalytic converter (which is in the factory down/engine pipe in the Forester) back to the rear
of the car. This exhaust replaces the restrictive centre exhaust pipe (either the original
Forester one or the WRX fitted in Stage 1) and rear muffler.
Improvements in the exhaust note are immediately apparent (you now get the nice ‘boxer
rumble’), without it being too loud or droning in the cabin. I installed MRT’s oval muffler
especially built for the Forester as it has a longer exhaust tip that extends to level with the
back bumper (a legal requirement). Many WRX specific rear mufflers are too short at the
exhaust tip.
The MRT muffler also seems to fit very nicely into the space that
exists to accommodate the muffler – there is an improvement in
ground clearance over the stock muffler (a bonus off-road), and
it is almost visually undetectable to the uninitiated, meaning it
won’t draw undue attention to your car – I liked this added
bonus.
Note: You may recall the ‘up pipe’ component of the exhaust
that fits between the exhaust manifold coming from the cylinders
and feeds into the Turbo charger. On the later models of
Forester (01-on) the up-pipe contains a catalytic converter
which is a restriction that robs power. Best bet is to replace it
with a pipe from a 99/00 WRX without the Catalytic Converter or
an aftermarket pipe such as the one MRT supply.
The earlier model Foresters don’t have the catalytic converter in their Up pipe, so no problem
if you have the early model like me – it saves you the hassle of replacing it, and the expense.
