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Upgrade Descriptions



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Off the showroom floor, the Forester is designed to have moderate understeer. Understeer is the condition where you turn the steering wheel but the car continues to go straight, refusing to turn in sending you possibly off the road or into a curb. To help remedy this there are larger rear sway bars that upgrade the tiny stock bar to a thick 18mm, 20mm or 21mm bar. 

The difference between the 20mm and 21mm is minimal with the 21mm giving you more oversteer compared to the 20mm, while the 18mm equals the front and keeps the vehicle more neutral. Sway bars, also known as anti-roll bars, reduce the car's tendency to lean over in turns yet do not degrade ride quality. 

With the larger rear bar you can more easily induce off-throttle oversteer. This means that when in a turn and the car begins to understeer, you can simply ease off the throttle for a split second and the front of the car will begin to point in towards the apex of the corner. Once you're back on your racing line, ease back into the throttle to power through the turn. On steady state, high speed cornering, the larger rear bar keeps the car more neutral, giving you more control and speed through the corner. Installation only takes a few minutes with simple hand tools.



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As your suspension works, the tops of the strut towers flex towards and away from each other reducing handling. To eliminate this, use a strut tower bar which simply bolts to the tops of the strut towers and braces them against any unwanted movement. This modification requires no drilling or permanent modification to the car and can be performed with ordinary hand tools in just a few minutes. Several manufacturers offer front strut bars, such as Cusco, STi, SYMS, and JC Sports.

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As with the front strut towers, the rear strut towers also suffer from flexing under load. Due to the fact that the rear strut towers are not located near any major chassis structure, they tend to flex even more than the front therefore installing a rear strut tower brace can make a very noticeable improvement even when using the stock suspension. The bar runs across the rear cargo area directly behind the rear seats. Simply remove the two bolts that hold the bar in place if you never need to temporarily reclaim the extra trunk/cargo space. Rear strut bars are offered by Cusco, STi, and TRi Tuning.



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For those who need to ability to increase camber beyond the narrow range allowed for by the factory setup, there are camber plates which replace the soft factory rubber upper strut mounts with high strength metal mounts and spherical (pillow ball) bushings. With these you can easily adjust your front negative camber well over the factory specs for much better handling. These units offer a FULL range of camber adjustment but the maximum negative camber allowed for will depend on your entire setup, including ride height. Designed to work with stock suspension or nearly every aftermarket system available. Benefits include:

Adjust camber & caster easily & SAFELY.
Very sturdy with absolutely no flexing and it bolts in.
Degree markings in place.  No need to second guess your strut angle.
Avoid the alignment shop, and messing with the stock camber bolts.

For those that do not need, or the rules for their racing class do not allow for, adjustable camber plates, there are also non-adjustable upper mounts in high strength metal with spherical (pillow ball) bushings. These units will greatly increase suspension response by reducing flexing and unwanted camber/caster changes. These are also designed to work with nearly every suspension kit available.

However, these kits are not for the long distance driver.  They transmit a lot of road noise to the cockpit.  There is no installation between the strut and the pillow mount, so you get to hear every thing your tires hit.  That is the major downside to the kits.  These mounts are available from both Cusco and Tein.

In addition to the aluminum mounts, there are also hard rubber strut mounts available from STI that are class legal for Group N rally racing. Some people feel these are the ideal street mounts because they are much stiffer than the stock mounts, but still allow a small amount of flexing and cushioning for daily driving comfort and quiet. 



There are many strut manufacturers that offer struts that will work in the Forester. Just remember, they are IMPREZA struts, front and rear. These are a few of the most common and easy to find.

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Subaru's own STi inverted struts for the Impreza WRX ver. 5 are considered an excellent choice for high-performance dampening duties on the Forester. When combined with a performance spring (like the ones from Fuji Heavy Industries, or Tein) they should provide excellent handling.

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The KYB GR-2 gas struts are affordably priced, twin tube designs that blend a smooth ride quality with enhanced road control. A low-pressure gas charge and patented check valve minimize foaming and aeration to help make sure the ride stays consistent, even under rough conditions. When you want to blend like-new vehicle ride qualities with a little more control, you want KYB GR-2 gas series complete struts. I am not 100% sure, but I believe that these are offered for stock-height Foresters.

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The KYB AGX Struts gives you the ability to tune your car's suspension to match conditions without sacrificing ride quality. Easily adjustable in a matter of seconds, the front struts offer 4 different dampening settings while the rear struts offer 8 different settings, allowing for proper tuning of the car's handling for the street, autocross, track or drag strip. The AGXs also feature a unique 3-valve system which constantly adjusts for the road conditions by making small, soft movements on smooth surfaces and automatically reacting quicker as the road gets rougher. These are currently the strut of choice for most Solo 2 competitors. These are only offered for the Impreza, which means their use on the Forester requires lowering springs.

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Prodrive Bilstein / Eibach Kits are also available. They received rave reviews in England. Non-adjustable and delivered as sets, these are some of the best sorted suspension kits available for ANY car. Large tube inverted struts tested by three time World Rally Champion Prodrive LTD.  The Prodrive GT gives the Impreza has a balance and poise few cars can match. The Prodrive WR Sport is set 20% stiffer and has superior 90mph + stability. Several very satisfied RS owners all agree - "superior performance." 

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LEDA manufactures a  2.5" coil-over suspension kit for Subaru vehicles. This setup made them British Touring Car Championship (BTCC) champions with Ford, and these coilovers are required on all FIA F1 Porsche Cup cars. These struts are 24 position adjustable for jounce and rebound. Best for experienced drivers. Completely adjustable spring rate and ride height. This kit was fitted to an Impreza 22b model and reviewed in a Dutch auto magazine: "Fastest car since the Ferrari F50 and the last Porsche 993 Turbo" Surprisingly good ride quality! These are competition units with rebuild-able struts. 



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Not only can you can improve handling and ride quality with a set of performance lowering springs, but they take away the "tippy-toe" stance of the Forester and make it look like a real road-burner! But, as far as I know, there are really only two good options:

Subaru (Fuji Heavy Industries) lowering springs. As the good people at iSR say, these will lower the front about 2.5" and the rear about 3.5" for a nice low, even stance. These are actually the stock springs from a 2.5 RS Impreza. The 1.5" lower height of the car combined with the additional weight of the Forester gives you the finished height. The picture on the left above is iSR's Forester with these springs and the STi Version 5 inverted struts. Nice. The one on the right above is my Forester with these springs and KYB AGX struts.

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Tein S-Tech Soft and Medium rate Forester Springs lower the front 2.75" (70mm) and the rear by 2.2" (55mm) for an aggressive look and better performance. They are available through Taka Kaira, Inc., in Japan and other Tein distributors worldwide. Unfortunately at this time, there is no U.S. Tein Distributor. I will keep you posted if and when that changes.


You can physically put Impreza lowering springs on the Forester. They will fit. But they will lower way too much. There is a picture of my Forester in the "MY FORESTER" portion with Tein Impreza Medium Springs. It really SLAMS it low. 

HOW LOW? I got about 4.5" lower than stock. It looked awesome, with my tires tucked in the rear. HOWEVER... beware. There is not enough wheel travel or strut travel to give you what sane people refer to as a real suspension. My wife began referring to my Forester as "The Blender." Tigger would be proud because it was BOUNCY BOUNCY BOUNCY! The 1.5" lower suspension of the Impreza combined with the 1.5" lower Tein springs combined with the additional weight is just too much. Plus, everyone of any expertise was in agreement, the struts cannot handle the inevitable bottoming out that occurs with no travel like that. They will fail. They will fail soon.  And KYB specifically denies warranty claims if the vehicle has been lowered more than 1.5". 

BUT the buck-board riding thing handles just like... a racecar. They bounce like a bronco over uneven roads too. I took corners (90 degree turns) at well over 40 mph without a hint of body roll or tire squeal. The fun more than made up for the discomfort. The FHI suspension, while comfortable, doesn't handle nearly as well. Maybe with some tweaks to the KYBs...

SO: If you plan to lower the Forester and you like some comfort in your ride not bruised kidneys, If you don't have the patience or the funding to replace struts every few months, stay away from Impreza lowering springs. Take it from me. You'll be sorry. I've done it. Or take it from iSR. They did it too. They are the ones that told me how to remedy the situation. Thaks iSR.



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Designed to exactly replace the restrictive factory air filter, the K&N performance filter is constructed with a pleated cotton gauze which improves air flow while maintaining a high level of filtration. Another unique feature of this filter is the ability to clean and re-use it by simply using the K&N cleaning chemicals and oil offered in their Re-charger kit. K&N even offers their famous 1,000,000 mile, 10 year warranty with this factory replacement filter, which means it quite possibly will be the last air filter you have to buy for your car. 50 State Legal (EPA and CARB).

Due to the delicate nature of the Subaru air flow meters, some tuners feel upgrading the in-box filter is your safest method of improving air flow into the engine without risking damaging your engine and/or electronic components. Other systems from various manufacturers, particularly those using foam elements, have resulted in many failures.

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Another power gain in the intake track is to remove the secondary air filter in the large air box just before the intake manifold. This must be replaced with a gasket of equal thickness to the filter, but by doing so, you remove the filter's restrictions from the intake track.

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Replacing the filter box altogether with a high flowing K&N filter is another alternative, and should yield a few more horsepower than just dropping in a replacement filter. Several  manufacturers offer kits to adapt these filters to the MAF & MAP sensors. iSR offers the intake kit shown above, which only replaces the airbox and secondary air filter for better top end flow, nut leaves the stock plenum which provides for low end torque. A similar adapter is available from ?? which adapts a K&N type cotton element filter to the MAF or MAP sensor for similar performance.

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Both TRi Tuning and Weapon-R Intake offer an all inclusive kit for the Subaru Forester.  Quality, sound, fit, and finish describe the both intakes.  The filter provides well for such a high flow unit.  The sound is pure joy, and with an average horsepower gain of 13-15hp on a '98 2.5 liter motor, this intake isn't just sound.  Pull from 4,800rpm to redline is improved substantially.  As for mileage, some have reported up to 2mpg improvement in the sub 3,000 rpm range at highway speeds.  Put your foot into it though, and with any performance unit, mileage will drop. The major difference between the two is that the Weapon-R actually loses some performance below 4,800rpm. The TRi Intake has a velocity stack attached to compensate and provide for low end torque.



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Built specifically for the North American-spec Forester, the Strömung exhaust systems were dyno proven to provide the largest gains of all the systems tested recently by Sports Compact Car magazine. Featuring smooth mandrel bent tubing and precision laser cut flanges, the Strömung exhaust systems fit perfectly with no additional welding or cutting required.

The Strömung performance exhaust systems are currently available in mild steel construction with a single tip 89mm tip for a more aggressive look and sporty exhaust tone. This system will provide an additional 4-6% increase in HP over stock throughout the entire powerband.

At this time, Strömung is the only company offering a complete cat-back exhaust system for the Forester. The only other choice is a custom-made exhaust utilizing a universal performance muffler such as one by 3A Racing.




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The stock Subaru headers are extremely restrictive and clearly built to save costs, not power. To remedy this inexcusable design flaw, there is the Borla Stainless steel headers. These headers feature nice, smooth mandrel bends with a much more effective layout which improves mid and high RPM torque and power. Currently, Borla offers a 2nd generation header with an improved design to offer better power gains and to address a rubbing problem found in the 1st generation headers. These are considered superior, for obvious reasons.

Not only do you gain performance but you also get the "boxer" sound the Subaru vehicles are famous for. This will transform the sound of the car under acceleration from a docile purr to a menacing rumble that sounds unlike any 4 cylinder engine you've ever heard. Sound quality at idle and cruise is increased only slightly.

The Borla headers are designed to bolt directly in place of the factory header system and therefore should be compatible with everything from 100% stock cars to car equipped with aftermarket turbo kits such as the Minnam system.

BORLA headers are built of aircraft-quality T-304 stainless steel - stainless inside and out, not mild steel, not aluminum, not coated aluminum, not just wrapped with stainless on the outside for show. Coating techniques, such as aluminizing, can somewhat prolong the life of mild steel, but coatings suffer at the weld points. And comparing aluminized steel to T-304 stainless steel is like comparing gold-plated metal to solid gold! T-304 stainless steel has the highest chromium content, making it the most resistant to corrosion and therefore the most desirable material for long-lasting exhaust system.



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Constructed from high quality billet aluminum, these power pulleys are CNC machined for a precise fit. Horsepower gains are realized throughout the entire powerband with an increase in peak power of approximately 6-8 engine HP. Most gains are a result of how much lighter this pulley is compared to the factory unit (4.5lb savings!!). Additional gains are a result of the slightly smaller diameter which underdrives the accessories for additional power. While this underdriving has no adverse effects on the reliability of the engine or components, it should be noted that when idling during heavy electrical load (ie: A/C on, upgraded stereo, etc) some owners might experience slight dimming of their headlights. Once RPMs rise back above idle, headlight intensity will return to normal. This is a very small tradeoff for the increase in performance and throttle response gained from this pulley.




Turbocharger Kits are offered by JC SPORTS. One offered is the IHI Turbo Kit is an easy bolt on kit that will give you a mild increase in power and torque.  It starts with 5 psi of boost and is easily upgradable to accommodate 8-10 psi.  At 5 psi you can expect an increase in horse power and torque of around 50%.  This is quite an increase if you look at it as horsepower per dollar.  This is a complete turbo kit that will include all necessary parts and hardware.  There is NO damage to the vehicle and you can return it to stock at any time (great for a leased vehicle).  One of the most impressive upgrades you can do to your SUBARU.  This is what SUBARU of America should have done years ago, instead of hiding behind the unprovable excuse that the WRX would not pass USA emissions laws.  Please note that cars equipped with turbo kits REQUIRE PREMIUM UNLEADED FUEL and it is recommended all turbo kits be installed by a qualified and experienced technician.


Supercharger kits are available from Rimmer Engineering. The Rimmer Performance System for the SOHC 2.5 liter Subaru boxer engine utilizes a series 2, .95 liter displacement Autorotor supercharger. Running 8 psi of boost through a 6 x 12 x 3 inch intercooler in conjunction with a rising rate fuel pressure regulator yields 230 hp! Your RS can now be as fast as it looks. 3 psi of boost available at IDLE, full boost is ready at 1600 rpm! Although the Drivetrain components are quite strong we recommend that you seriously consider an improved clutch setup, but is within the capabilities of the automatic transmission. Since the Forester does not have a hood scoop, it cannot use the air / air intercooler and instead requires the use of an air / water intercooler setup, like the one below installed on a Subaru Outback.

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NOTE: Recently I heard an rumor (from two different, un-affiliated companies) that Rimmer is out of business. I also heard that they can be difficult to get merchandise from, even after they have been paid. These may or may not be true, just remember one thing...

Caveat Emptor. (Buyer Beware.)



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The complete 2" body lift kits from Scorpion consist of solid aluminum block spacers, all steel parts are laser cut and zinc plated. Bolts are high tensile strength & detailed instructions are simple and easy to follow. Ride quality is unchanged with the body lift kit.

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Scorpion replacement springs will add another 2" of lift to the Forester platform. These springs have a higher spring rate and reduce down travel, affecting the ride quality slightly.

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These pictures from iSR's web site show the burgundy Forester with the 4" of lift from the two kits, and comparison photos show the difference to the black Forester's stock height.