2004 Impreza WRX STi

WRX STi Builds On Subaru CoreTechnology

• Horizontally opposedengine

• Simple, symmetric AWDlayout

• Long travel, independentsuspension

• Lightweight

• Excellent balance

• Lower center of gravity

Engine

• 2.5-liter horizontally opposed 4-cylinder• Turbocharged with intercooler• DOHC 16 valve

• 300 hp @ 6,000 rpm• 300 lb-ft @ 4,000 rpm

• Largest displacement engine fitted into any STimodel– Unique to North America

Hood Scoop

• Large hood scoop feedsoutside air to the intercooler

Intercooler

• Larger capacity intercooler (30% larger than WRX)• Outside air is ducted through the intercooler from hood

scoop• Air to air exchanger removes heat from intake air into

engine• Cooler denser air contains more oxygen for improved

combustion and performance

Intercooler Water Spray System

• System is manuallyoperated by the driver

– Momentary switchactivates a 2 second oncycle water spray

• Water spray jet locatedover intercooler

– Water sprayed overintercooler absorbsadditional heat fromintake air, increasingefficiency of theintercooler

• Water tank located in thetrunk on the right sidequarter panel area

– This location aids in theeven distribution ofweight in the vehicle

– Water stays cooler

I/C Water Spray Switch

I/C Water Tank

Engine

• IHI brand turbocharger– 14.5 PSI maximum boost pressure

• Electronic Throttle Control (ETC)– Smoother throttle operation and response– Reduced emissions

Active Valve Control System (AVCS)

• Active Valve ControlSystem (AVCS) is avariable valve timingsystem

• Intake valve timing isadvanced or retardedto increase combustionefficiency

• Engine performance isincreased by optimizingboth low end torqueand high endhorsepower

• Improved fuel economyand reduced emissions

Active Valve Control System (AVCS)

• Engine Control Module(ECM) controls operationof the oil control valvesbased on engine inputs

• Oil control valves locatedon both cylinder headsuse engine oil pressure torotate the intake camsprockets relative to theintake camshafts– Oil is feed into either the

advance or retardchambers in the intakecamshaft sprocket

Oil Control Valve

AVCS Intake Cam Sprocket

Active Valve Control System (AVCS)

• ECM computer mapprograms are used toprovide optimum valvetiming for:– Low RPM Range

Stable smooth engineidle

– Mid RPM RangeImproved fuel economy

– High RPM RangeMaximum engine output

• Valve overlap is theamount of time both theintake and exhaust valvesare open simultaneously

Minimum valve overlap LowRPM Range / smooth idle

Advanced valve overlap Mid RPMRange / intake volume increases andrecirculated exhaust gases improve

fuel economy

Maximum advance valveoverlap high RPM Range /

increased intake volume dueto scavenging effect

Engine Features

• 4 valves per cylinder DOHC

• Reduced reciprocating mass:– Hollow intake valves– Hollow camshafts– Shim-less valve lifters

• Reducing the reciprocating massincreases engine performanceand fuel economy

• Sodium filled exhaust valvesimprove heat transfer

• Iridium Spark Plugs– Higher melting point than

platinum– Less energy to create a spark– More durable

Engine Features

Open Deck Engine Block

Semi-Closed Deck Engine BlockIncreased block rigidity

Engine Features

• Rear crankshaft journalutilizes a Metal MatrixComposite (MMC) insert

– Aircraft technology– Lightweight composite

provides high strength

• Reduced NVH– Composite has equal

expansion rate of crankshaftfor journal clearance

• High-strength, lightweight castaluminum-alloy pistons– High heat resistance– Low thermal expansion

• Forged high carbon steelconnecting rods

Flywheel and Clutch

• Solid flywheel is used for highperformance applications– Provides a more rigid surface

for solid engagement

• Clutch diameter has beenincreased from 9.0 inches forthe WRX models to 9.5 inchesfor the WRX STi model– Provides a larger surface for

increased grip.

• Higher clamping force

Pressure Plate

Clutch Disc

Flywheel

6-speed Manual Transmission

• 6-Speed Manual Transmission with Driver ControlCenter Differential (DCCD) Full-Time All-Wheel Driveas standard equipment– An automatic transmission is not available

• This new 6-speed transmission is a heavy-duty highperformance design developed to handle the highengine output of the WRX STi.

6-speed Manual Transmission• Double-cone synchronizers on 1st, 3rd and reverse

gears• Triple-cone synchronizers on 2nd gear• Single-cone synchronizers on 4th, 5th and 6th gears

– Increases durability– Reduces gear clash when shifting– Provides a smoother performance feel

• Transmission has a pressurized oil lubricating system– The oil pump pressurizes and feeds lubricating oil to the

mainshaft, pinion shaft and the gears– Conventional transmissions use a splash lubrication

system

6-speed Manual Transmission

• Close ratios on 1st, 2nd

and 3rd gears

• Close ratio is when thetransmission gearratios are steppedclose together in size– Allows the engine to

stay in the optimumoutput range whenshifting

• Compared to WRX, anadditional gear isutilized between 1st and4th

Gear Ratio Chart

2.3751.9472nd Gear

0.9710.7385th Gear

1.3460.9724th Gear

3.6363.4541st Gear

0.756-6th Gear

1.7611.3663rd Gear

WRXSTi MT6

WRXMT5

Shifter• Short-throw shifter

– Gear to gear lever longitudinal and lateral movementis decreased allowing quicker engagement

• Reverse lock-out mechanism on the shifterassembly– Engage reverse gear by lifting up on lock-out ring and

moving the shifter completely to the right and back– The reverse lock-out mechanism prevents accidental

shifting into reverse.Reverse Lock-out Ring

Shift Pattern

Driver Controlled Center Differential (DCCD)AWD

• The most performance-directedSubaru All-Wheel Drive system

• Planetary center differential splitsengine torque 65% rear 35% frontnormal driving conditions

• Increased handling agility andperformance driving feel

• Two modes: Automatic andManual

DCCD with Automatic Mode• Planetary center differential provides a performance-

oriented 65% rear 35% front power split

• The transfer clutch assembly utilizes a pilot clutch andmain clutch which allows the system to use a small, lightelectromagnet to vary the lock-up and power distribution– Eliminates the need for hydraulic control

Planetary Carrier

Main Clutch

Electromagnetic Clutch

Pilot Clutch

DCCD with Automatic Mode• Cornering Control• Torque split

between the frontand rear wheelsautomaticallyadjusted dependingon driver input, roadconditions andcornering forces

DCCD Manual Mode

• Using control dial switch, drivercan select from 6 levels ofdifferential locking

• Locking ratio progresses from65% rear 35% front to 50:50front to rear

• Indicator in instrument clustershows the level of powertransfer selected

DCCD Indicator

DCCD Control Dial Switch

DCCD Manual Mode

• Allows the driver to customize All-WheelDrive performance:

– Weather conditions– Road/pavement surface conditions– Suit a particular driving style

Front and Rear Limited-Slip Differentials

• Suretrac® front differential• Mechanical clutch type rear differential• Heavy-duty for high output engine• Tighter control than the limited-slip

differentials used in other Subaru models• Some noise is normal

Suretrac® FrontDifferential

Integrated intoTransmission

Mechanical Rear Differential

Suretrac LSD Front Differential

• Gearless unit that responds to atorque difference between the frontwheels to increase traction and helpreduce understeer

• Provides smooth, progressive steering

Suretrac LSD

• Utilizes face cams and cam followers to providedifferential action and transfer torque to wheel with thebest traction

• Face cams are formed with a series of inclined rampsthat resemble teeth

• To provide smooth, progressive steering, a difference inwheels speeds causes the cam followers to move backand forth, ramping up and slipping over the face cams

Face CamsCam Followers

Suretrac LSD• Under normal road conditions, driving straight, no front

wheel slippage, rotational wheel speeds are the same

• Under this condition the cam followers are forcedagainst face cams and turn as a unit

• Torque is transmitted uniformly through the camfollowers to the face cams and to both front wheels.

• Limited slip function is regulated by spring tension andmechanical friction between the face cams and the camfollowers.

Engine Torque Applied

Cam FollowersForced Against

Face Cams

Uniform DrivingForce toWheels

Mechanical Limited-Slip Rear Differential• Mechanical limited-slip rear differential

provides tighter control between the rearwheels

• When one rear wheel begins to losetraction, a rotational difference in the leftand right wheel speed occurs– This causes the carrier pinion gear shaft to

expand the pressure rings and sandwich thefriction discs and plates together

– This creates a physical connection betweenthe side gears and the differential carrier andapplies the limited-slip function

• Application of limited-slip depends on theamount of torque being applied– Under high torque, the differential locks

Mechanical Limited-Slip Rear Differential

PressureRings

Carrier Pinion Gear Shaft

Friction Discs & Plates

Side GearsDifferential Carrier

Inverted Strut Performance Suspension• Suspension draws directly from rally-winning experience

– Proven durability from WRC competition

• Forged aluminum-alloy front L-arms reduce unsprung weight• Stabilizer bar links incorporate ball joint type ends instead of

rubber bushings– Direct connection between sway bar and suspension reduces

body roll and increases stability when cornering

Front Suspension Rear Suspension

Aluminum-alloyL-Arm

InvertedStruts

Inverted Struts

• Rally-derived inverted struts increase lateral rigidly

• Inverted struts allow extremely high cornering loadswhile providing consistent performance under varyingdriving conditions– Increased strut bending resistance– Maintains proper wheel alignment when cornering

Inverted Struts• Functions like a

conventional shockabsorber set upside-downand covered by anothertube

• Strength of the outer steeltube rather than theinternal piston rod bearsthe brunt of bending forcesacting upon the strut duringcornering

• Piston rod rides in thelower portion of the struttube rather than the uppersection

• Larger upper strut tubeallows a larger piston areafor better dampeningcharacteristics

Inverted StrutConventional Strut

Brembo® Performance Brake System

• Brembo is the supplier to Ferrari Formula One andchampionship winning racing teams around the world

• Larger discs increase clamping force and brakeleverage, increasing brake torque

• Front:– 12.7-inch diameter ventilated discs– 4-piston fixed calipers

• Rear:– 12.3-inch diameter ventilated discs– Twin-piston fixed calipers

RearFront

Directional Front Calipers

• As the calipers clamp the brakerotors, the pads want to travelforward with the discs whichcauses uneven wear becausethe rear of pads wedge intodiscs

• Leading, lower pistons aresmaller in diameter and the toppistons larger in diameter inorder to counteract unevenbrake pad wear

Front Discs

• Braking generates heat, andthe larger discs can absorband dissipate more heat forgreater fade resistance

• Discs use a pillar-type vanedesign (comprised of manysmall posts) for ventilation– The pillars are not continuous

across the disc to help preventheat distortion and warping

– Pillars are multi-sided toincrease the surface area forbetter cooling

Super Sport ABS• Helps reduce understeer and enhances stability under hard

braking when cornering

• Helps reduce stopping distance when cornering comparedto conventional ABS

• Utilizes input from a lateral g-sensor to individually controlbrake pressure to each rear wheel

With Super Sport ABS

Without Super Sport ABS

Crossmembers• A cross bar was added to reinforce the front

crossmember– Increased lateral rigidity to help prevent

suspension flex

• Support braces were added to the rearcrossmember body mounting area– Crossmember mounting bushing rigidity

increased– Increased lateral rigidity and help

prevent suspension flex

Support BraceBushing

• Wheels:• Lightweight BBS brand

• 17 x 7.5-inch• Forged aluminum-alloy• Gold or silver painted option

• Performance Tires:• Bridgestone Potenza RE 070• Summer, Directional

• 225 / 45 R17 90W

Wheels and Tires

DirectionTreadDesign

End, Thank you

IMPORTANT INFORMATION

The Supplemental Restraint System (SRS) (air bags) affords the driver and front passengeradditional protection in a moderate to severe frontal or (when equipped with front seat head/chestside-impact air bags) a side-impact collision. This system provides supplemental protection only,and seatbelts must be worn in order to avoid injuries to out-of-position occupants upon bagdeployment and to provide the best combined protection in a serious accident. Children shouldalways be properly restrained in the rear seat.

Specifications are based on the latest product information available. Subaru of America, Inc.,reserves the right to change or discontinue at any time, without notice, prices, colors, materials,equipment, accessories, specifications, models and packages without incurring any obligation tomake the same or similar changes on vehicles previously sold. Colors shown may vary due toreproduction process. For more information, contact your Subaru dealer. Subaru, Outback,Legacy, Forester, Impreza, Baja, WRX, WRX STi, L.L.Bean, MOMO, BBS, Brembo, SuretracMcIntosh, Ecsaine, Switchback, OnStar and SCCA are registered trademarks. “DRIVEN BYWHAT’S INSIDE.” is a trademark.

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