Subaru launched the third generation Japanese and world-market Legacy in June 1998, while the North American model was introduced in May 1999 for the 2000 model year. In all markets except for the United States, production lasted through 2002, with a limited production Blitzen model sold mid-cycle under the 2003 model year in Japan. Production in the United States lasted through 2004.
At its introduction in 1999, it won the Automotive Researchers' and Journalists' Conference Car of the Year award in Japan.
All models were equipped with standard, symmetrical all wheel drive. World-market and Japanese models ranged from a naturally aspirated or twin-turbo 2.0-liter flat-4 to naturally aspirated 3.0-liter. Even though dimensions became mid-sized, it was still rated by the EPA as a compact car.
Flat roof wagons are no longer manufactured worldwide, and instead the raised roof is used for both the Legacy and Outback wagons (Lancaster in Japan).
In late 2000, the EZ30, a newly designed 3.0 L H6 was offered in the Outback and Lancaster (Japan) models.
The Legacy was the only vehicle in this class that provided AWD as standard equipment.
Architecture
B4 The B4 model was introduced for the third generation and was a sedan-only model. The RSK meaning "Rally Sport Kompressor" featured the familiar DOHC, twin-turbo 2.0-liter engine rated ( for automatic with manual mode). This results in a 0–60 mph (97 km/h) time of 5.2 seconds for the manual and 5.8 seconds for the automatic. This engine was popular with Japanese buyers due to reduced tax liability based on Japanese vehicle size legislation; the car offered performance advantages over larger cars sold in Japan with bigger engines but with a smaller tax bill. The B4 moniker also applied to naturally aspirated models, such as the 2.0 L TS-R.
Australia models (called B4) were detuned to run on lower octane (98 RON) fuel and were rated for the manual and for the automatic models. This results in a 0–60 mph time of 5.6 seconds for the manual and 6.6 seconds for the automatic.
A B4 TS-R model was equipped with a less powerful, naturally aspirated 2.0 L DOHC AVCS engine, but shared many of the body and suspension components of the more powerful RSK.
In 2001, a B4 RS25 model was introduced with a naturally aspirated 2.5 L DOHC engine.
In 2002, the B4 RS30 was introduced with a naturally aspirated 3.0 L EZ30 DOHC flat-six engine.
B4 Engine Structure
The B4 is powered by a 'phase 2' all-alloy DOHC, 16-valve, intercooled turbo 2.0-liter boxer four. According to official Subaru literature, there are several advantages to the boxer design. Due to the balance afforded by horizontally opposed cylinders, the crankshaft requires less weighting and so there is no need to install balance shafts. This results in reduced noise, vibration and less power loss from the engine. Strength is also an advantage of the boxer design – the crankshaft is sandwiched between the left and right hand crankcases and is supported by 5 main bearings. The low and wide engine structure also lowers the vehicle's center of gravity and improves mass distribution.
Working from the crankcases out, the 'phase 2' engine sees the crank thrust bearing relocated to the rear of the shaft – this reduces the transfer of natural frequencies to the transmission, resulting in reduced NVH. Improved off-boost torque comes from a raised static compression ratio – 9.0:1, compared to the Impreza WRX's 8.0:1.
Sequential Turbo Staging
The B4 uses a sequentially staged primary and secondary turbocharger to deliver good throttle response and a wide torque spread. The primary turbo delivers boost in the low rpm and load ranges to deliver at 2000 rpm, while the secondary turbo joins in above 4000–4500 rpm. With both turbos boosting, a torque peak arrives at 4800 rpm and maximum power () is seen at 6000 rpm. Note that Japanese-market B4s – running on 100-octane fuel – are rated at .
The primary turbo (located at the left rear of the engine) delivers boost in the low rpm and load range, while the secondary turbo comes in to aid mid-to-high range breathing. During the primary turbo stage, boost pressure is controlled by a conventional arrangement of an ECU-controlled duty-cycle solenoid and an internal wastegate.
The secondary turbo remains inoperative during this stage, as a separate exhaust control valve (situated on the right side of the engine) remains closed. This valve prevents exhaust gasses from entering the secondary turbine.
During the 4000–4500 rpm transitional stage, however, the exhaust control valve is partially opened, bringing the secondary turbo up to near-operating speed. The ECU – working with another duty solenoid and vacuum diaphragm – determines the amount that the exhaust control valve opens. The ECU calculates this amount of valve opening based on the input of a differential pressure sensor that takes feeds from the intake manifold and the outlet of the secondary turbo.
Any boost pressure produced by the secondary turbocharger during the transitional stage is redirected to the atmospheric side of the compressor inlet (between the turbos and air filter).
With the primary turbo continuing to supply manifold pressure and the secondary turbocharger essentially bleeding off the boost it makes during the transition, the ECU will determine when to close the pressure relief valve and fully open the exhaust control valve. Once this is done, the ECU will again look at the input from the differential pressure sensor and open yet another valve – the intake control valve (which is mounted between the secondary turbo's compressor outlet and the intercooler).
With the intake control valve open, boost pressure from the secondary turbo is allowed to pass through the intercooler (in addition to the boost supplied by the primary turbo). Manifold pressure during the second stage of turbocharging remains regulated by the primary turbocharger's wastegate – there is only one turbine by-pass valve in the whole system.
Subaru claims: "The 'staging' between the single and twin-turbo operating range, which was quite noticeable to the driver on the previous model B4, has now largely been 'tuned out' by the careful selection of turbocharger size and the controlling mechanisms. As can be seen from this torque curve, however, under some driving conditions it is still possible to detect a slight reduction in the rate of acceleration in the preparatory or intermediate phase that occurs between 4000–4500 rpm."
The Turbochargers
Despite being called twins, the B4's turbochargers are not identical. The primary turbocharger is an IHI VF33 unit (RHF4 core - floating metal thrust bearing design), which uses a 46.5 / 35.4 mm 9-blade turbine wheel and a 47.0 mm / 35.4 mm 6 + 6 blade compressor. At idle, the turbo spins at around 20,000 rpm and it can go on to a maximum speed of 190,000 rpm. It has a 17 mm diameter wastegate opening to bypass excess exhaust gas. The secondary turbocharger is an IHI VF32 (RHF4B core - ball bearing design). On the exhaust side it uses a 46.5 / 35.4 mm 9-blade turbine wheel, teamed with a 52.5 / 36.6 mm 10-blade compressor wheel. It's rated at 180,000 rpm.
Intercooling
Like the WRX, the B4 uses a bonnet scoop to feed a top-mount air-to-air intercooler. Manufactured by Sanden, the intercooler has an effective depth of 73 mm, a width of 140 mm and a length of 370 mm. With 26 tubes to take induction air from one end-tank to the other, the unit has a 13.37 kW heat transfer capacity and reduces 120–130 degree Celsius charge air to 70–80 degrees Celsius (claimed).
Gearbox and Driveline
Australian-delivered Liberty B4s come with a longitudinally mounted 5-speed manual gearbox only. It is essentially the same unit that was introduced in MY99 models (which saw the most changes since the Liberty was introduced in 1990).
Amongst its list of improvements is increased case rigidity and twice the number of bolts attaching it to the engine (eight instead of four). The synchromesh baulk ring, gear docking teeth angles and the double cone synchro on 2nd and 3rd gear have also all been retuned.
The B4's 'S type' close-ratio gearset has taller ratios in the first three cogs than the Impreza WRX, but a shorter 4.11:1 final drive ratio counters some of this effect. The gears are now cold forged and shot peened for added strength and a flexible flywheel design is now incorporated to reduce engine vibration reaching the driveline. The pull-type 230 mm single plate clutch has increased torque capacity thanks to an 830 kg clamping load pressure plate.
The B4's AWD layout is traditional Subaru. The viscous limited-slip center coupling apportions front-to-rear torque 50:50. Torque distribution at the road, however, is dependent on load distribution and tyre grip. As a result, the static straight driving ratio is 60:40 front-to-rear. Under dynamic driving conditions, however, the torque distribution varies accordingly. The viscous coupling senses rotational speed difference between the front and rear axles and transmits torque to the end with the most grip (which has lesser axle rpm).
A rear viscous LSD is also used to improve high-speed stability and traction during low-speed cornering.
Suspension
The B4 is suspended on the same platform as other Liberty models – MacPherson struts under the front and an all-new multi-link rear Chapman strut arrangement. The front suspension incorporates cast aluminium L-shaped transverse links and the cross member features a newly devised 'performance rod'. The performance rod is a lateral brace, which improves side-axis stiffness by 500 percent and longitudinal stiffness by 50 percent. This provides more constant suspension geometry under hard cornering. The rear suspension, too, receives an additional support sub-frame to improve rear suspension lateral and longitudinal stiffness (by 200 percent and 20 percent respectively).
The struts are inverted to deliver higher bending rigidity (thanks to larger damping tube diameter) and less damping fade as a result of increased piston size. Springs are mounted offset so their centerline coincides with the pivot axis. This reduces road shock and – by minimizing bump and rebound friction – provides less vibration.
The B4's initial spring, damper, and swaybar specifications were devised in Japan and later tuned at the Nürburgring circuit. It's said the target was to at least equal the performance of the BMW M3.
Braking
The B4 is slowed by 294mm ventilated front disc brakes and twin-pot floating calipers and 290mm ventilated rear discs and single-pot floating calipers. An increased diameter vacuum assisted tandem booster gives reduced pedal effort though relatively firm braking feel (see graph). The system is diagonally linked to maintain safety in the event one line should fail, and front and rear pressure control valve are used to balance braking force to suit weight distribution. Maximum braking deceleration from 100 km/h is 0.99g with a 39.4 metre stopping distance.
The B4's standard anti-lock braking system is Bosch's 5.3i system (which is made under license by Nippon ABS). It's a 4-channel, 3-phase system with the front wheels controlled individually, while the rears are controlled jointly (through the 'select low' method). The select low method uses the rear wheel with the lower coefficient of adhesion to calculate the brake line pressure applied to both of the rear wheels.
The aforementioned 'select low' method of rear braking force, together with electronically delayed buildup of braking force at the front wheel with a high adhesion coefficient and negative steering roll radius, maximises chassis stability under braking.
Electronics