2009 Subaru Impreza STI - Engine & Transmission

The new JDM Impreza WRX STI will be powered by a revised version of the semi-closed deck 2.0L boxer engine with a twin-scroll turbo, equal length manifold and introduces a drive-by-wire throttle and Dual Active Valve Control System (Dual AVCS). The Dual AVCS hydraulically controls timing in both the intake and exhaust valves (previous models only had control of the inlet side), which helps improve low-end torque while providing a strong power delivery at high rpm. This significantly improves the engines efficiency and allows the STI to develop 90% of its peak torque from as little as 2,400rpm. Dual AVCS also increases combustion efficiency, thereby reducing exhaust emissions. The new engine now has 308PS (304bhp) at 6,800rpm and 311 lb-ft (422Nm) of torque at 4,400rpm. However as with all of our JDM Subaru's the ECU is recalibrated and tuned for the UK's fuel and these new improvements mean we will be able to offer even greater performance on this new model. The new 2009 Litchfield car comes with a revised free flow filter which lifts our standard power to 325bhp and 315lbft after our Ecu reprogramming. This figure improves drastically when mated to our new high flow exhaust system and induction package featured in our Performance package.

Like all the great car engines the STI's engine was developed with one eye firmly on its motorsport performance and durability with the JDM 2.0litre engine being FIA Homologated for Group N rallying. Subaru have created an extremely powerful and strong engine that can more than handle the increase power levels and stress placed on it by GroupN rally events (where the engine internals must remain standard). The engine is also blessed with advanced features only found on the JDM model which combine to make a much more dynamic engine package. This strength and advanced design mean that the engine also response extremely well to further tuning and optimisation.

Key components to the JDM model's outstanding power is the engine's use of a Twin-Scroll turbo and equal length exhaust manifold which manage the exhaust flow and pulses much more efficiently by avoiding interference between the Exhaust port and Turbo. These essential parts allow the JDM engine to build boost far faster than the conventional Euro/US designs, virtually remove turbo lag and dramatically improve throttle response. This more efficient setup also allows the engine to rev higher and smoother than the older setup. The JDM STI also features larger Intake and Exhaust ports which further improve flow, combustion efficiency, producing a reduction in emissions and improves fuel consumption. The cam shaft profiles are also more aggressive to suit the larger power band and changes in the shape of the turbocharger compressor have increased the efficiency of the air intake enabling more responsive and smoother acceleration. Because of the JDM STIs competition background it also features a improved cylinder head design with larger Sodium filled valves for increased durability at high temperatures.

These many detailed upgrades coupled with the improvements gained from the introduction of the Dual AVCS means the engine is blessed with significant low down torque and high end power delivery. With power building from as low as 2,400rpm all the way to the 8,000rpm redline giving not only better peak power and torque numbers but more importantly access to these higher levels for a much longer period.

The 2.0litre JDM STI engine features improved fuel efficiency over the previous models and especially when operating within the Intelligent Si-Drive mode. The engine is significantly Greener than any previous STI engine and the JDM STI produces lower emissions and C02 levels than any other world versions. The JDM STI now also features Emission reducing technology like inlet-tract tumble valves and secondary air system which dramatically improve the emissions performance from the moment the engine is started.

Another first for the new STI is the integration of Subaru Intelligent Drive (SI-Drive). This amazing system was first introduced on the 2007 European Legacy 3.0 litre Spec B and Outback range and also on the Japanese turbocharged models. This new system gives the driver the option to refine performance and fuel economy to suit their preferences by choosing between three preset engine modes; Intelligent, Sport and Sports #. SI-Drive regulates the engine and fine-tunes the electronic throttle control. SI-Drive can optimize fuel efficiency in stop-start city traffic, produce a lively response in flowing Motorway or town traffic, or a rapid sporty drive on open roads. The three modes are clearly displayed on the instrument panel and are quickly changed by rotating or pushing the Si-Drive dial.

Intelligent mode allows gentle, smooth power output with greater economy in congested city driving at low to mid-speed or when combined with a smooth driving style on high speed roads. In this mode the Dash also flashes a small green light at the optimum gear change point. Subaru's internal testing indicates a vehicle driven in intelligent mode gains a 10 per cent improvement in consumption.

Sport mode optimises performance on city and open road drives offering a compromise for day-to-day driving.

Sport # mode this mode further sharpens the engines throttle response allowing the enthusiastic driver to receive maximum acceleration and performance. Litchfield Imports also tailors the SI-Drive settings for UK roads, fuel consumption is improved further at our higher Motorway speeds in Intelligent Mode and both Sports modes feature increased power and torque.

Coupled with the new DCCD control system never before has a Subaru driver had so much control of the cars setup and power delivery for any give situation or environment enhancing enjoyment.

Delivering this advanced engine power to the chassis is Subaru's 6-speed manual transmission, already exceptionally good, which has been further perfected for faster, more accurate and responsive shifts. Friction is substantially reduced through the adoption of a triple-cone synchromesh in the first gear and design changes in the shift sleeves. The previous gearbox comfortably managed 600+bhp and flat-shifting in our Championship winning Race STI.