Actually Subaru has already raised the bar, 2.5liter sti has been for sale for a while. MY06 wrx and sti will be with 2.5liter engines, still 4bangers, but nothing beats CIDs as they say.
http://www.type-25.com/engine.asp
Power through more than just displacement
Subaru’s ubiquitous 2.5lite (EJ257) block first appeared in the 300bhp US STI then later in the Forester XT/STI and soon in new 226/276bhp European models. The EJ257 has been a necessary development for Subaru as they expand in world markets and have to tackle increasingly tough emission levels such as the enforced EuroIV emission standards in January’06. This 2.5 engine has allowed Subaru to meet these requirements whilst maintaining their high performance philosophy.
Although suitable for factory power targets the EJ257 has a number of short comings and limitations when looking to produce serious power. Early Type25 development showed up weak points which were carefully addressed in the production versions. For example the Type 25 featured unique forged pistons fitted in the engines build process and these have proved extremely reliable unlike the standard hypoeutectic cast pistons that can reveal their brittle construction at higher power levels. In fact in the new 2006 Type 25 the only parts left of the original EJ257 engine are the outer casing and bearings. The new Type 25 features Pistons and Conrods that are both stronger and lighter forged items than the standard Subaru parts, even the crank is checked and balanced before fitting.
One of the key reasons for basing the Type 25 on the Japanese Domestic Market STI, aside from the higher chassis/equipment levels, is that the engine in the JDM car is much more advanced than the European or US versions. The Japanese car features a better cylinder head design which, with careful modification, allows far better flow rates that the European and even its standard EJ257 cylinder heads. The Japanese car also features larger ports which further improve flow and the Cam Shaft profiles are more aggressive allowing a larger power band. These improvements also allow better use of the Variable Valve Timing features which further broadens the engines mighty low down torque and high end power delivery.
Another key component to the JDM models outstanding power is the engines use of the Twin Scroll turbo and equal length exhaust manifold. These essential parts allow the JDM engine to build boost far faster than the conventional Euro/US designs and virtually remove turbo lag and dramatically improve throttle response. The more efficient setup also allows the engine to rev higher and smoother than the older designs. The Type 25 takes the Twin scroll concept to a new performance level by using heavily modified parts while retaining all the JDM engines’ clever engineering.
The retention of the Twinscroll design allows the Type 25 to use larger turbo internals which still deliver ultra fast response whilst remain capable of supplying the 2.5 engine with ample air much higher up the rev range than the conventional Euro/US models can manage.
The use of an advanced exhaust and improved inlet system allows the Type 25 to pump more air in and out of the engine whilst adhering to strict noise and emission legislation.
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