2009 Litchfield Type-20 - Twinscroll Turbo

One of the most important improvements seen on the Type-20 is the design of its bespoke turbo. For possibly the first time in the UK tuning industry a turbo has been manufactured specifically for a performance model. Previous Turbo upgrades had seen hybrid versions of the original equipment (Type-25 Mk1) or the adaption of an off the shelf model that would achieve the desired performance target (Type-25 Mk2). This new turbo marks a significant investment into producing the ideal solution and highlights the level of commitment Litchfield takes in its performance models.

This new twinscroll turbo will bolt directly onto Subaru’s excellent equal length manifold and allows the fitment of our proven Milltek exhaust system. The performance targets for the new turbo were extreme tough. We wanted a turbo with spool up and response that would match or bettered the standard Twinscroll turbo but the design would also have to allow much greater airflow at higher rpm. This is the holy grail of Turbo design after many months of testing and R&D, in conjunction with our technical partners Turbo Dynamics, Litchfield have been able to produce their new Twinscroll turbo.

Litchfield having been tuning the standard Twinscroll turbo since they launched their JDM STI in 2003. This experience has given a thorough understanding of what they can achieve and where any potential restrictions lie. We have worked with Turbo Dynamics for years on various hybrid versions of the Turbo and after much testing they were able to advice on the best standalone solution for our more powerful Mark 2 Type-25 models.

With the launch of the new Impreza STI and Subaru’s continued use of the excellent VF36 style Twinscroll turbo design the decision was taken to develop not only a bolt on replacement for our new models but also a replacement turbo that many of the older MY03+ Subaru imports could use.

The Turbo is designed in 2 versions; one for the Japanese 2.0 engines, like the Type-20 and another for the larger 2.5+ engines. Over the years Litchfield have tested a number of standard Twinscroll turbos along with some of the Japanese aftermarket Twinscroll models both on 2.0 and 2.5 litre engines.

These turbos were then sent to Turbo dynamics were the expensive process of slicing their exhaust housings into multiple sections began. Each section was then digitally scanned with 2D and 3D computer models generated. This long and complicated process allows for a complete understanding of the internal turbo Volute design and shape. From here we were able see how the different turbos achieve their gases flow performance. We were also able to observe areas where subtle and significant improvements could be made. Turbo dynamics were also able to cross reference the internal sizes with other turbo designs that have been proven at over 550bhp.

The new computer design for the turbo exhaust housing is then past onto pattern makers and casting of the new design can begin by an experienced OEM Turbo casting foundry insuring the highest quality and experience. Once cast the exhaust housings are sent to Turbo Dynamics engineering shop where detailed machine work is performed to insure the perfect finish and Subaru port matching. All of these processes take place in the UK using the latest technology and very best expertise.

The new Exhaust housing is made from the very best Ni Resist Iron which surpasses most turbos on the market. The Ni Resist also insures the best resistance to heat and a high quality surface finish. The detailed 3D modelling, shaping, accurate casting and machine work also give improvements to gases flow over and above the internal volute size.

The Twinscroll or Divided entrance design maintains the separate exhaust paths from the firing cylinders. This stops the cycles interfering with one another until they reach the inside of the turbo and better utilises the engine's exhaust pulse energy. Because of the efficient use of the exhaust pulse energy, the turbine's performance is improved and boost builds more quickly aiding throttle response.

The new exhaust housing design allows the simple interchanging of Garrett ball bearing cores and wheel trims allowing us to match our power and response demands accurately with our component choice. Garrett Ball Bearing turbochargers spool up 15% faster than traditional journal bearings and have been proven to be very durable in both OEM and high performance applications.

However the innovation and attention to detail does not stop with the internals of this new turbo. The outside of the exhaust housing is treated in the advanced Zircotec ceramic coating. The company's plasma-sprayed ceramic coating is proven at the highest levels of motorsport, with five grand prix teams amongst their customers for the high-tech thermal barrier. Litchfield first used Zircotec in 2006 on the 415bhp Subaru Type-25 and it produced excellent results. This advanced coating helps maintain the heat energy where it is needed inside the turbine and exhaust which gives additional benefits in turbo response and power. The coating also helps reduce under bonnet temperatures.

Turbo Dynamics are also casting a new compressor cover which will be used on our new Turbo this too will offer a superior internal design and finish. Together with low back pressure 3” Milltek exhaust system and smooth flowing cold air intake the new Turbo is able to exceed our performance demands through innovative design and advanced technology.

Litchfield hope full production versions of this exciting new turbo will be available by the end of the year.