Jump to content
LegacyGT.com

Recommended Posts

[b][size=7]Part 1: General Subaru & Legacy Info[/size][/b] Considering there are generally many questions, what body style is what, what did this model contain, yada, yada, here is some info to explain things. It will be updated as time presents itself and details become available. I will do my best to explain info. If something somehow seems inaccurate, feel free to voice. [b][u]Basic Terminology & Acronyms[/u][/b] 4EAT – Four Speed Electronic Automatic Transmission 5MT – Five Speed Manual Transmission 5EAT – Five Speed Electronic Automatic Transmission (includes Sportshift) 6MT – Six Speed Manual Transmission ABS – Anti-lock Braking System AT – Automatic Transmission ATF – Automatic Transmission Fluid AutoX – Autocross AVCS – Active Valve Control Sysem AVLS – Active Valve Lift System AWD – All Wheel Drive BHP – Brake HorsePower (measured BEFORE transmission) BOV – Blow Off Valve CAI – Cold Air Intake Cat – Catalytic Convertor CEL – Check Engine Light CF – Carbon Fiber CO2 – Carbon Dioxide Diff – Differential DOHC – Dual Overhead Camshaft EBC – Electonic Boost Controller ECT - Electronically Controlled Transmission ECU – Electronic Control Unit (engine control unit) EFI – Electronic Fuel Injection EG – Subaru 6-cylinder engines (up through mid to late 90’s) EG33 – Subaru 3.3 litre 6-cylinder engine code (SVX) EJ – Subaru 4-cylinder engines (early 90’s and newer) EJ20 – Subaru 2.0 litre 4-cylinder engine code EJ205 – Subaru 2.0 litre turbo engine (US WRX) EJ22 – Subaru 2.2 litre 4-cylinder engine code EJ25 – Subaru 2.5 litre 4-cylinder engine code EJ255 – Subaru 2.5 litre turbo engine (US Forester XT, Baja Turbo) EJ257 – Subaru 2.5 litre turbo engine (US WRX STi) EZ – Subaru 6-cylinder engines (post EG series H6 engines) EZ30R – Subaru 3.0 litre 6-cylinder engine code (BL/BP Legacy and new Outback) FDR - Final Drive Ratio FMIC – Front Mount Intercooler FWD – Front Wheel Drive H4 – Horizontally Opposed 4 cylinder (boxer) H6 – Horizontally Opposed 6 cylinder HID – High Intensity Discharge (headlights) JDM – Japanese Domestic Market LSD – Limited Slip Differential MAF – Mass Air-Flow Sensor MAP – Manifold Absolute Pressure Sensor MBC – Manual Boost Controller MIL – Malfunction Indicator Lamp (CEL) MT – Manual Transmission MY – Model Year OEM – Original Equipment Manufacturer RallyX – Rallycross RWD – Rear Wheel Drive SOA – Subaru Of America SOHC – Single Overhead Camshaft TMIC – Top Mount Intercooler TT – Twin Turbo UDP – Under Drive Pulley VDC – Vehicle Dynamic Control VIN – Vehicle Identification Number VTD – Variable Torque Distibution WHP – Wheel HorsePower WOT – Wide Open Throttle [size=2][i]Thanks to Uncle Meat of the Cobb Tuning WRXForum.com[/i][/size] [b][u]JDM (Japanese Domestic Market) Info:[/u][/b] [b]Twin-Turbo:[/b] This is one of the most loosely used term. Everyone wants a twin-turbo because Japan has had it. It was a sequential setup with one turbo used for the low end, while a larger turbo was used for the high end. However, it wasn’t the most optimal solution being its cost, complexity, and between the 1st to 2nd turbo transition, there was a decent dip in power. It has been proven that other solutions are more cost-effective and produce better results in general. More on turbo tech below. [i][b]B4:[/b][/i] The term used for sedan since the 1998 model year. [i][b]B4 RSK:[/b][/i] The name given to the turbocharged sport Legacy Sedan in the 1998 to 2002 model years. Remember, Japan has been even further ahead in model changes. They receive their models 2 model years (or MY) ahead of the U.S. Note: Previous to the BE-generation B4 RSK, the sedan turbo models were called ‘RS’. [i][b]GTB:[/b][/i] The name given to the turbocharged sport Legacy Wagon in the 1993 to 2002 model years that used the sportier Bilstein suspension. [i][b]S401:[/b][/i] The ONLY STi production Legacy to date. This 2003 BE sedan model was produced in a short-run and were rather expensive. It contained much gear from the current year Impreza STi though mostly in drivetrain and brakes. It still retained a sequential twin-turbo setup though with a few more ponies. It also received some suspension modifications including Bilstein struts along with BBS 18x7” wheels. [b][u]Body Styles (by USDM MY):[/u][/b] [i]Sedans[/i] BC (1990-1994) BD (1995-1999) BE (2000-2004) BL (2005-2009) [i]Wagons[/i] BF (1990-1994) BG (1995-1999) BH (2000-2004) BP (2005-2009)
Link to comment
Share on other sites

[b][size=7]Part 2: Engine Tuning[/size][/b] [u][b]AVCS & AVLS[/b][/u] Subaru has been adding some 'active' systems that in addition to the normal operating action of the engine are able to vary certain components to increase power and efficiency. Two of these systems, AVCS (Active Valve Control System) and AVLS (Active Valve Lift System) are very new to Subaru, with the latter being new this year and only available on the EZ30R as far as we know. [b]AVCS[/b] is a system that works with the cams (usually only on the intake side where the most benefits are shown) to adjust the duration of the intake valve opening, closing, and rates of change depending on what the computer determines according to sensor input. The AVCS system is actuated through oil pressure from the engine, which is sent through a computer controlled valve and then directs oil into an AVCS actuator to advance or retard cam timing in respect to the cam sprocket. The best thing about the system is that, the same heads can be used with or without AVCS activated. It’s just an auxiliary system in essence. [b]AVLS[/b] is another new technology to help improve volumetric efficiency. While AVCS can alter the cam duration and angle, either advancing or retarding the valve timing, AVLS is able to use two different profiles to alter the valve lift. The EZ30R is the first Subaru engine to use this technology. Instead of using a system like Honda’s VTEC with two cams, Subaru uses a double-profile single cam to control the same parameters. Much like the AVCS setup, AVLS actuates the switch between low and high lift lobes through an oil-actuated system. This system uses a double-tappet (the components which is in contact with both the valve and cam as shown below.) The switchable tappet switches between the low-duration and high duration generally in the 2,000 to 4,000 rpm range depending on ECU input (much lower than VTEC) allowing the EZ30R to breathe better at high rpm and improve low-rpm torque as well as emissions. [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/H6internals.jpg[/img] A good description is also offered in [url=http://subaru.com.au/news/?newsid=11894]THIS[/url] press release. [u][b]Exhaust Design[/b][/u] One of the best tech write-ups on the key characteristics of exhaust design can be found [url=http://www.cobbtuning.com/tech/exhaustdesign/index.html]HERE[/url] on Cobb Tuning’s website, written by Josh Tenny. It is very informative whether you have a naturally aspirated or turbocharged Subaru. [u][b]Intake Tech[/b][/u] These articles describe some of the complications of intakes regarding Subaru’s choice of sensors and how they work with the entire intake track along with many other aspects. [url=http://www.cobbtuning.com/tech/airflow/index.html]Subaru’s Intake System Discussion (MAP vs. MAF)[/url] [url=http://www.cobbtuning.com/tech/intakes/]The use of Aftermarket Intakes on 2002+ Subaru factory-turbocharged vehicles[/url] More to come!
Link to comment
Share on other sites

[b][size=7]Part 3: Drivetrain[/size][/b] [b][u]Transmissions & Gearsets[/b][/u] The first and foremost part of the drivetrain is the transmission. This is the component mounted just rear of the Subaru boxer engine. This key assembly hosts several very important parts including but not limited to the front differential (located at the front lower portion of the case), the center differential (located at the rear of the unit just ahead of the tail shaft), and the complex geartrain. Subaru offers a few different flavors of transmissions depending on application and user choice: *5-Speed Manual *6-Speed Heavy-Duty Manual, *4-Speed Automatic *4-Speed Automatic with Sportshift *5-Speed Automatic with Sportshift. Though the each manual or automatic transmission has a good deal of similarities to the others of it’s type (ex. 5MT and 6MT), the automatic and manual types in themselves vary greatly from each other in both components and how they function. [b]Manual Transmissions[/b] While many know Subaru has been using 5MT’s for quite some time, many don’t know the history behind the current unit in use. The [u]overall[/u] design of the 5MT dates back to the early to mid 1980’s as the basic design was conceived to be used with the naturally aspirated 1.8L engine of the day producing around half of the power as the current WRX produces. This gearbox has evolved plenty over the 20 or so years of its lifespan for increased strength, reliability, and smoothness. The 5MT design in general is rather reliable given modest power levels and being driven smoothly. The problems only arose after the WRX started to become widely available, the USDM in particular. While the 5MT is just fine in a very high percentage of instances, problems have arose with that small percentage of owners and drivers who like to slam through gears, do hard launches, and flog these machines just like any 2WD car. It’s not like a 2WD car where traction is going through one or two wheels and then up in smoke, the WRX has 3 traction surfaces (the open front + viscous center and rear differentials transmit power effectively to a minimum of 3 wheels) which places much greater loads on the internal components of the transmission (which few owners that destroy their transmissions understand.) Previous to bringing the car to the USDM, the rate of failure (including high-output STi models with the virtually the same tranny) was MUCH lower, which shows how abusive the American crowd is in general. The new 5MT units placed in the ’04 Forester XT first, now ’05 Legacy 2.5GT, and WRX turbocharged models are said to have received a strengthened case to reduce case flex which may have contributed a substantial effect to the proverbial ‘straw that broke the camels back’, though that doesn’t place any less blame on those who clearly abused their transmissions. From all evidence so far about the Forester XT and from the models in Japan that have supposedly started receiving this new case revision as early as MY02, it is substantially beefier and harder to break leading evidence of malfunction more directly to abuse. [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/open6MT.jpg[/img] The STi-exclusive 6-speed manual transmission (seen above) is similar in function to the 5MT, but has received a major overhaul in design. While it operates somewhat similar to the Subaru 5MT in feel, it has recieved a much beefier case, shorter ratios (6 gears instead of 5), a transmission oil cooler with pump built-in, and segregated oil galleys to reduce the potential of chips to be spread around as most notable upgrades over the basic 5MT design. This transmission is built to handle a substantially greater amount of power over the 5-speed unit, though same effect if drivers flog them in similar order. The STi transmission also includes a Drivers Controlled Center Differential (DCCD) that has the ability to bias power where needed (automatic mode) or desired (manual mode); anything between a full 50:50 lock and nearly a 2:1 rear bias is available. For those requiring the most durable and performance-oriented solution that is just as much at home on the streets as it is at the track, this is currently the butcher’s prime cut of meat. [b]Upgraded Gearsets[/b] For those who require an even stronger 5MT gearbox, several companies provide strengthened gearsets of various designs to aid in durability at elevated power levels and under extreme conditions. There are two main options aside from doing an entire conversion to the STi 6MT unit, which is very comprehensive and complicated for most. The first solution is similar to the standard synchro gearset used as original equipment, but replace the gears with ones that use a smaller gear pitch meaning you will have less teeth in the same diameter, however, each tooth will be thicker and therefore, stronger. Of this type of upgrade, the most popular solution happens to be the STi RA gearset shown below left in comparison with OE gears to compare tooth profiles. Other companies that make good synchros gear sets include but are not limited to: APS, MRT, STi, and Quaife to name a few of the most well known manufacturers. [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/thumbRAgear.jpg[/img] [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/APSgearset.jpg[/img] [i]Shown in the visual from APS on the right, the parts highlighted in red show what is generally replaced while upgrading the gearset.[/i] The second option is to go with a dogbox. A dogbox varies from a synchro gearset in that it lacks synchronizers, which bring the input shaft from the engine up to speed with the output shaft going to the wheels. Synchronizers take up space where gears could be made wider and stronger. In place of synchronizers are dog teeth and the additional width of the gear for extra strength. To bring the input shaft up to the speed of the output shaft; rev matching must be used by the driver to make the transition from one gear to the next as smooth as possible and reduce drivetrain shock. [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/fulldogbox.jpg[/img] Dogbox transmissions are basically a race transmission for the reasons listed above and more. They are advantageous over even the STi 6MT in many race-only applications as it uses straight cut gears which are able to take greater abuse and power levels due to the design of the teeth, which produces no end thrust unlike helical gears which in extreme cases can distort the transmission case by the tendency of the gears to wanting to push/pull. Using the dog teeth for engagement can actually allow experienced professional racecar drivers to shift faster and more efficiently. The major drawback to this solution additional to the advanced skill level required to master shifting the dogbox if required for a road car is the noise of the gearbox due to the straight-cut gear design (technically referred to as ‘spur gears’), which is one of the main advantages of the helical-cut pattern used in most road cars. These are all reasons why this is basically a race-only setup, though some people do run half dog-boxes in the lower gears for extreme road applications. Definitely not for the faint of heart though! Seen below is a good comparison with gears out of a dog box on the left and a gear out of a regular Subaru synchro transmission on the right. Notice the synchro gear has a helical (helix-type) cut pattern while the gears from the dog box are straight cut. The standard helical gear on the right has a synchronizer (generally known as synchro) shown just above the gear as looking to have many small teeth. The dog teeth are shown in the same position on the opposing gear on the left. Note these teeth can NOT mesh. For proper meshing characteristics, gears must have the same pitch. [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/dogsynchro.jpg[/img] Well, now that we know a bit about the Subaru manual transmission, we want to understand where each component sits and how it actually works. Coming Soon! [b]Automatic Transmissions[/b] [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/5EAT.gif[/img] Coming Soon! [b][u]Differentials & Electronic Input[/b][/u] [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/b5diff.gif[/img] Differentials are a very important part of any drivetrain. They are the components that move power between the transmission and axle shafts, changing the direction of power and final gear reduction (through the ring and pinion gears as seen below.) These aspects all help to give you the proper power balance to keep the vehicle under control. While 2WD cars use a single differential to transmit power to two axles, Subaru’s and other AWD cars require three; the center, which transfers power fore and aft from the transmission to front and rear units which transfer power side to side. However, not all differential types are created equal as each is tailored to a specific type of driving and set of conditions. There are a number of types of differentials applicable to the Subaru drivetrain with two main categories: [b]Open[/b] and [b]Limited-Slip[/b]. The main difference being limited-slip units maximize traction by sending torque to the wheels with the most traction which they essentially lock while still allowing a variation in speed for turning. Limited Slip differentials comprise of several different designs including, but not limited to: [b]Viscous Coupling[/b], [b]Torsen[/b], [b]Clutch Type[/b], and [b]Electronically Controlled[/b] units. The main types of differentials applicable to Subaru drivetrains are described in further detail below. One main thing to keep in mind is the size of the rear differential however, as most general road applications use an R160 (160mm ring gear), if more power is desired and especially if an STi 6-speed manual transmission is being installed, an R180 sized rear differential with associating shafts and hubs is nearly a must to keep reliability in check. An R200 size is available but is only required for the absolute highest output race machines. [b]Open:[/b] This is the most common type of differential used for it’s relatively low cost, lighter weight, and generally predictable vehicle dynamics. This type of differential is used in the front differential in nearly all Subaru’s other than more recent STi models. It is also still used in many of the lower level models for the rear unit as well. This type of differential distributes power fairly evenly to both wheels in a straight line, but when one wheel starts to slip, power follows the path of least resistance, which is unfortunately the slipping wheel. This type of differential is therefore NOT considered a Limited Slip Differential. It is not considered optimal for racing and frequent driving on low traction surfaces though adequate for most transient driving conditions. [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/PS84Diff1.gif[/img] Please check out [url=http://static.howstuffworks.com/flash/differential.swf]THIS[/url] animation to see how open differentials work. [b]Torsen (TORque SENsing):[/b] The Torsen differentials (also known as Helical differentials because of one of the main components- helical cut gears, also known as worm gears) are a mechanical type of differential, no clutches, fluids, or electronic controls involved. This type of differential is excellent because it has nothing to wear out and does not wait for the loss of traction to take effect. Torsion units use a pair of helical cut gears that work like an open differential when power is equal. When a difference in traction is sensed, the helical gears go to work and bind together sending a predetermined amount of torque to the wheel with more traction. The torque bias is predetermined by the design of the helical cut. The only drawback of this type of differential is that when one wheel or set of wheels looses traction, the torque bias defaults to zero torque transfer. A simple remedy of tapping the brake while staying on the throttle produces enough of a level of traction that shifts power to the wheel with traction. Despite this small and less than likely occurrence for most drivers, this is the preferred type of differential for many drivers and some manufacturers due to it’s fast acting characteristics, safe and predictable handling, and it’s very positive ability to reduce torque steer. Audi’s Quattro system has used this type of differential for several years (though information points to just as the center differential lately with Electronic or some other forum of LSDs front and rear) because it works well with ABS sensors, it allows power to move smoothly until things get tricky, and then sends power to where it’s needed most. The Quaife ATB (Anti-Torque Biasing) units are probably the most well known, though STi also sells Helical units and others are available as well. [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/PS84Diff3.gif[/img] For more info on this type of unit, consult the [url=http://www.quaifeamerica.com/]Quaife America website[/url]. [b]Viscous Coupling:[/b] This type of differential is used in most of Subaru’s performance-oriented vehicles (RS’s, GT’s, WRX’s, etc.) in the rear location, while being used in the center location for nearly all late model Subaru models. Viscous coupling differentials have the ability to better transfer power to the ground in situations where wheel slip occurs versus open style differentials while still being cost effective. How does this work? The viscous coupling units use two sets of plates close together that are surrounded by a thick fluid. When one set of plates starts turning faster than the other (one wheel or set may be slipping), the thick fluid in the differential heats up and brings both sets of plates to the same speed essentially locking them together. The only drawback is that this system doesn’t kick in until wheels actually start spinning at varied speeds (greater than just a normal turn) while some other units start working when a difference in torque is detected. [b]Clutch-Type:[/b] [img]http://www.kaazusa.com/images/lsd_exploded_view.jpg[/img] [size=1]Image courtesy of KAAZ USA[/size] This type of differential works similar to the open differential design in normal driving, as do most of these types of limited-slip differentials. However, as viscous units use fluid and torsen units use mechanical gears to essentially lock two output shafts or bias them to a given ratio, this system uses clutch packs as seen in the image above. These clutch packs are made up of alternating friction discs (splined to the back side of the Side Gear) and friction plates (splined to the differential case.) These two clutch packs (one per each axle) reside between the end of the case and a cast pressure ring (which rotates with the case it’s splined to), which essentially butts up to the side gear. [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/clutchdiff.gif[/img] When one axle spins, slower than the rotating case, the pinion shaft shown in the middle (looks like a 4-way) rotates against the V-grooves of the pressure ring putting increased pressure back on the plates causing them to lock when enough pressure is applied. A spring plate and disc is generally used on each side to lessen the impact when the two plates do lock. To gain the desired results, plates and discs of varying thickness can be combined for desired locking results. This type of differential needs to be picked extremely carefully as it can potentially have very undesirable results. In many (not all) instances, understeer becomes more prevalent as both wheels are trying very hard to spin at the same speed, thus the car will want to push straight no matter how much the driver tries turning. This type of differential is generally favorable more on low traction surfaces such as gravel and snow where equal power to the ground through both axles may be desired. With the right setup though, such as the Suretrac design found on WRX STi’s, a good balance can be found for street/tarmac applications. [b]Subaru’s DCCD (Driver Controlled Center Differential:[/b] Better than can be described here, [url=http://www.canadiandriver.com/articles/jk/031210.htm]the Canadian Driver[/url] effectively describes how Subaru’s special center differential unit available only on STi models works, and works very well! [b]Dynamic Stability Programs:[/b] Subaru relies mainly on mechanical means of safely propelling their vehicles, at least mainly on the manual transmission models. For the automatic transmission enabled vehicles, they use a combination of VDC (Vehicle Dynamic Control), VTD (Variable Torque Distribution), and ATS (Active Torque Split) additional to the already present Viscous Center Differentials. These systems are all controlled with the center differential located within the transmission case. [i]VDC[/i]- takes input from an array of sensors about data including vehicle speed, engine speed, steering wheel angle, gear, and brake status to constantly monitor the conditions and to try and alleviate a potential danger before the car gets out of hand. Several who have tried this system have said it isn’t geared as much for sport as it is for safety, which is good for the average driver, but not the enthusiast. This feature is exclusive to the high-end Outback H6 models thus far. [i]ATS[/i]- has been around since the early 1980’s in Subaru automatic transmissions. This simple setup though similar to VDC just senses power at the axles, gear selection, accelerator position, and vehicle speed without the vehicle dynamics included in the VDC setup. This system takes all the data and calculates how much power to send fore and aft for optimal safe results. Best said on the Subaru of New Zealand website, in basic terms ‘it automatically transfers power from the wheels that slip to the wheels that grip.’ [i]VTD[/i]- is a slightly sportier tune of the ATS system allowing more power (up to a 36:64 F:R torque split) to the rear wheels or up to a 50:50 ratio depending on driving conditions. This is the system used in the Legacy GT (at least through USDM/CDM MY04), WRX’s, and some of the other sportier models. For more information considering Subaru’s Active AWD electronic input systems, consult [url=http://www.subaru.co.nz/Roam/Subaru_Advantage/]Subaru New Zealand’s website[/url] and the [url=http://www.subaru-global.com/about/awd/2300.html]Subaru Global’s Drivetrain Info Page[/url]. Some of the best information and diagram sources: [url=www.howstuffworks.com/differential.htm/printable]HowStuffWorks - Differentials[/url] [url=http://www.canadiandriver.com/articles/jk/at_010410.htm]Canadian Driver - Differentials[/url] [url=http://www.marklines.com/en/presen/tochigifuji.jsp]Fuji presentation Comparison[/url] [url=http://www.houseofthud.com/differentials.htm]General Differential Info[/url] [url=http://members.rennlist.org/951_racerx/PS84Gleason.html]History of the Torsion Differential[/url] [b][u]Clutches & Flywheels[/b][/u] The new Legacy manual transmission models incorporate a dual-mass flywheel setup which is designed to reduce jerkiness and noise, and make everyday driving easier. For those who want something a bit more, lightweight flywheels are available, though it is recommended purchasing one at least 12lbs or greater as lower a weight unit may make drivability suffer. Lightweight units allow the engine to rev up faster, increasing performance. Of the current designs available, Chrome-Moly fabricated units appear to have the optimal strength with the ability to be lightweight as well. Upgrading power in Subaru AWD cars puts an even greater stress load on transmission, and since power is being transmitted to a minimum of 2 wheels (up to 4) in 2 different directions through the transmission case, many recommend keeping the stock clutch, or some type of aftermarket full face clutch with less than 50% greater holding power over stock. 3-Paddle style clutches (a.k.a. 3-puck/button) aren’t recommended for street applications as they tend to shutter and are more abusive to transmissions, particularly in ample-traction environments. Full-Face Style [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/thumbRST1000.jpg[/img] 3-Puck Clutch Style [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/thumbRST1002.jpg[/img] [b][u]Hardened Mounts & Bushings[/b][/u] These components are designed to reduce driveline and engine movements to transmit power more effectively to the ground, though there will be a noticable increase in NVH with many of these mounts.
Link to comment
Share on other sites

[b][size=7]Part 4: Chassis[/size][/b] [b][u]Suspension[/b][/u] This is an area that really allows an individual to tailor the vehicle to their driving needs and desires. Some of the most common types of suspension components are listed below along with what they do and what kind of impact they make on handling or if they’re basically just for aestetics. [b]Strut Tower Bars[/b] [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/2-6.jpg[/img] While being pertinent to many vehicles to increase chassis rigidity, older models in particular, strut tower bars (which span from the top of one strut tower to the opposing tower, mounted over the coil-over assembly) have become less useful in the latest Impreza models as well as even the BE/BH (2000-2004) Legacy models due to the absolute strength and rigidity present in the newest chassis. The new Legacy should further improve over the last making STB’s virtually useless in sedan models unless you want the look, and functional basically in just the rear location for wagon models. [b]Sway Bars, Mounts, and Endlinks[/b] Sway bars are probably one of the best handling modifications available to reduce body roll and understeer (the tendency for the nose to keep going straight while you want to turn.) Choosing an appropriate sway bar size (generally 19-22mm without upgraded front bars, or up to 24mm with upgraded front bars) will make a very noticeable handling difference, and considered by many to be one stage one-type modifications. Some things that must be taken into consideration though is with bars set to 20mm and higher, the stock mounts may break, thus aftermarket companies are starting to ship hardened mounts with their bars to alleviate this problem. Otherwise, they can be found separately. Additionally, endlinks may want to be upgraded as well, particularly with going to a higher set sway bar diameter, as the increased stress could make these more prone to breaking and their effectiveness becomes reduced. (At press time I am unaware if the USDM models have upgraded to new steel units I have seen pictures of which may negate the need for upgraded end links. I am only aware of this on the Legacy models however.) [b]Springs & Struts (and Coil-Overs)[/b] [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/RST2100.jpg[/img] The chassis is really held up by two main components off the axles, springs and struts (also known as shocks.) The springs suspend the body of the car and everything attached to it, while the struts ensure the tires stay in contact with the road with a high-pressure gas. There are many different options with this setup, but it is highly recommended that the struts and springs be matched for optimal performance, safety, and to minimize chance of damage to the suspension equipment. This setup can come in the form of a ‘coil-over’ which is essentially a spring and strut in a unit, many of these aftermarket units are adjustable by spring rates (the higher the weight, the harder they will ride) and stiffness of the struts (known as dampening rates.) More widely used (particularly by OEMs) are a combination of springs and struts. There is a growing line of sport springs available for the Legacy models while finding applicable struts is hit or miss for many model years. Most springs lower the chassis by about 1” giving it a slightly more level stance while increased spring rates give the car a more supple ride. There are many solutions available for the Impreza chassis currently, and we may see at least a couple of the better solutions available for the Legacy chassis within the next year. As good as springs and struts are at reducing body roll and increasing agility, they work best when coupled with at least a heavier rear sway bar or matched set (designed for the perfect handling balance- not the same size as match may be interpreted as) of front and rear sway bars. [b]Control Arms, Bushings, & Links[/b] [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/2-2.jpg[/img][img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/thumbRST2000.jpg[/img] To keep the suspension of your vehicle as responsive, quick acting, and rigid as possible, upgraded bushings, rear lateral links, and aluminum front control arms are one of the best kept secrets in the book. Subaru uses softer bushing and heavier steel suspension components to keep cost and NVH down on their normal street cars. What many don’t know is that for many of the road going cars, FHI produced STi versions of these components that are more rigid, lighter, and have better bushings to reduce unsprung weight, help your car respond faster with better feedback, and track better with increased alignment precision. Sometimes it’s the little things that really count. [b]Alignment[/b] [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/thumbRST2030.jpg[/img] If you are planning on racing your Legacy or the alignment shop doesn’t meet your specs, you may want to check out aftermarket Strut Top Mounts and/or alignment bolt kits which allow you to tailor your alignment to your specific needs (like race days) and can help provide a more sturdy alignment with even greater range of settings. [b][u]Brakes[/b][/u] [img]http://homepage.mac.com/futureofx/.Pictures/LSTIHOST/brakedisc.jpg[/img] The brakes on the new Legacy GT incorporate vented discs front and rear. The front disc size is 12.3” x 1.18” thick while the rear size is 11.3” x 0.7”. Dual-piston floating calipers are fitted up front with single floating sliding calipers are out back. The combination of near STi-sized brakes up front and basically WRX-sized rotors out back, both vented, will assure fade-free (loss of braking due to excessive heat) driving, even on the most spirited drives. This setup should not require the upgrade of calipers unless under the most extreme race conditions such as extensive lapping days. Some ways to improve pedal fell and bite are to incorporate stainless steel brake lines and upgraded pads. While upgrading pads, if you desire OE-like dusting and sound characteristics (or lack-there-of), Ceramic-type compounds are desired which keep dusting to a minimum while having an increased pad bit, heat range, and few require any bed-in. If you desire/require pads that bite harder and have a higher temp range, semi-metallic pads are available. Do not though, most of these pads dust heavily, squeel when cold, do not operate well below summer driving temps and are optimal only during higher temps such as tracking days. This type of pad also wears rotors faster. [b][u]Wheels[/b][/u] When purchasing wheels, the specs require a 5x100 bolt pattern (the SVX and new '05 WRX STi uses a 5x114 pattern.) To reduce the possibility of rubbing, premature wheel bearing failure, and un-normal forces being placed on tires, wheels, and suspension components, the wheel offset should generally stay within this recommended range: 6.5" ....... +53 to +55 7.0" ....... +50 to +53 7.5" ....... +47 to +50 8.0" ....... +43 to +47 This is a general recommendation for Subarus as not all fit each model (stock 2.5GT wheel is 7" wide while 2.5i models recieve a 6.5" wheel.) Recommended wheel dimensions for the Legacy line includes: -16x6.5" (stock 2.5i wheel) -16x7" -17x7” (stock 2.5GT wheel, smallest size usable for GT) -17x7.5” -18x7” -18x7.5” Wider wheels such as 8" wide may fit the new Legacy, we have just not seen any evidence of this yet. [b][u] Tires[/b][/u] This is by far one of the most crucial part of your car. Be sure to take good care of them, and get the right ones! Saving $10 on tires to get some off brand just isn’t worth the trade-offs. This all starts with good homework. So what do you need to know about buying the right tires? Most important is if this is a street tire, keeping your stock rolling-diameter. The 205/55R-16 and 225/45R-17 tires have about a 25.1” diameter where the 215/45R-17 optional on the WRX (and will be on the new GT) is about 24.8”. Stick to a range of about 24.7” to 25.2” to keep your odometer semi-accurate and mileage decent. Make sure to see what your OE tire size is though as these are close but not exact figures. This doesn’t mean you have to stick at 17” if you want 18” wheels or likewise with 16’s. If you are purchasing tires online, sources like Tire Rack give you an excellent resource center to help you be informed about your tire selection. Things to look for in addition to the diameter include: -Specialty of tire (all-season high performance, summer, competition, etc.) -Width of wheel it requires -Speed rating (VR, WR, etc. explained later) -Max inflation -Load rating -Treadwear rating (the lower- the faster you’ll chew them up, but the stickier they usually are) Ironically, some of the better tires out there cost much less and far outperform many of the high priced models, so just don’t judge a tire by it’s price! Additionally, many sites including The Tire Rack, 1010Tires.com, and other sites rate how well the tires perform as rated by other buyers and the company selling the tires. Treadepot.com and OnlineTires.com are two more that provide a decent cost with plenty of available options. A reference of generally applicable sizes: 205/55R-16 225/50R-16 205/50R-17 215/45R-17 225/45R-17 215/45R-18 225/40R-18 [size=2][i]Note: 16” wheels & tires will not fit new 2.5GT models as 17” wheels are required to clear brakes.[/i][/size] Speed Ratings: H- up to 130mph (210km/h) V- up to 149mph (240km/h) W- up to 168mph (270km/h) Y- up to 186mph (300km/h) Z- over 149mph (240km/h) An excellent reference for more information regarding tires is Tire Rack’s own [url=http://www.tirerack.com/tires/tiretech/tiretech.jsp]Tire Tech[/url] section.
Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.



×
×
  • Create New...

Important Information

Terms of Use