APS S/R Series Ball Bearing Turbochargers Finally, a range of high performance direct replacement turbochargers that have been specifically designed for the Subaru WRX/STI by the Subaru performance specialists - APS. APS has designed and produced what is arguably the ultimate in bullet proof turbochargers for the Subaru Impreza enthusiast.

Unencumbered by the limitations of current off the shelf WRX turbochargers, APS has totally engineered a "no-compromise" series of turbochargers from the ground up to match the exact requirements of high performance Subaru Impreza engines.

High strength compressor wheel design, ball bearing construction and high nickel content turbine housing means complete reliability to pressure ratios over 3:1 (30 psi!). And since nobody likes to wait, the APS S/R Series turbochargers are designed for fast spool-up to provide crisp turbocharger response.

Best of all, the S/R range of turbochargers are complete bolt on. Simple hook up of all factory connections and full compatibility with high performance inlet/exhaust means that the installation of your APS S/R Series turbocharger is truly no hassle.

If you want ballistic power and outstanding turbocharger reliability in a truly bolt on high performance unit, then the APS S/R Series turbocharger the perfect choice.

Available in a range of 3 turbocharger power output sizes to over 550 hp (410 kW), APS provides an S/R Series turbocharger that is optimum for engines from mild 2.0L through to wild 2.5L. The APS S/R Series Turbochargers are complete with all ancillary equipment for a truly bolt-on performance upgrade to the Subaru WRX/STI.

APS SR40 Turbocharger - P/N 990-060-425

The SR40 turbocharger is a specialist performance turbocharger with performance characteristics to suit modified WRX engines of 2.0 - 2.2 L capacity. The SR40 turbocharger has the capacity to supply air to produce 440 hp with good turbocharger response characteristics. Compressor Turbine A/R 0.60 0.82 Inducer 53.0 mm 54.0 mm Exducer 76.2 mm 47.0 mm

Supplied with WRX style oil hose to suit all wrx & '06 model STI.

Why Twin Ball Bearing?

Demands for improving acceleration response and for the reduction of so-called turbo lag are popular amongst performance enthusiasts who wish to take advantage of the enormous gains in power and torque delivered by turbochargers. In addition, bullet-proof reliability is required particularly at high turbocharger boost pressure levels as well as at extreme exhaust gas temperatures commonly found in high performance turbocharged engines.

In order to achieve crisp turbocharger response, a number of advances in turbocharger design have been utilized over the past decade. Primarily through the use of modern metals/ceramics in order to reduce the mass of the rotating assembly. However, significant gains have been made by reducing the friction of the rotating assembly - and this has meant a departure from traditional turbocharger designs.

Traditional turbocharger design employs a conventional plain bearing that runs on a film of oil. This is known as a floating metal bush.

The diagram above shows the turbocharger main shaft supported by floating metal bushes. Oil is fed through the bushes and forms a cushioning layer between the turbocharger shaft and the supporting bush. The shaft relies on a constant supply of fresh, clean oil over a very wide contact area in order to maintain sufficient clearance from the bush itself. A similar approach is used to support the turbocharger main shaft from thrust loads as well.

Whilst floating metal designs have served us well in the past, the frictional forces are relatively high. This results in sluggish turbocharger response and can be somewhat fragile in nature under extreme operating conditions.

Nissan attacked this very issue some 15 years ago on the GTR Skyline by developing a turbocharger bearing system that forms the basis of the true high performance modern turbocharger.

By utilizing robust ball bearings at either side of the turbocharger main shaft, this did away with the floating metal and thrust bushes.

As seen in the diagram above, the turbocharger shaft is supported by two ball bearing assemblies. These again are fed with engine oil, but no longer rely on a thin film of oil over a wide area to support the turbocharger shaft.

The result is an outstanding reduction of frictional torque on the rotating turbocharger assembly in contrast to the old fashioned floating metal bushes. The improvement in turbocharger response, particularly in the lower to mid turbocharger speed range is phenomenal.

The graph above shows frictional torque versus turbocharger speed of both old fashioned designs and modern ball bearing turbochargers. Clearly evident are the improvements with ball bearing turbochargers - especially at the low speed range of under 60,000 RPM where friction losses are reduced by 40% to 50%. This translates directly into a quantum leap in turbocharger response.

To show this in another way, the above chart demonstrates the mechanical efficiency advantage of the dual ball bearing design compared to journal (floating metal) and hybrid ball bearing turbochargers. The improved mechanical efficiency of the dual ball bearing design results in exceptionally crisp and strong throttle response over that of lesser turbocharger designs. This produces an improved response that can be converted to quicker 0-60 mph times.

Reduced Oil Flow

The dual ball bearing design reduces the required amount of oil to provide excellent lubrication. This lower volume reduces the lubrication load upon the entire engine lubrication system and allows more oil flow to vital engine components - resulting in improved engine durability.

The oil flow through the turbocharger is contolled precisely through an innovative oil flow control module that also acts as a highly effective debris separator in order to keep potentially harmful foreign particles from entering the turbocharger bearing assembly.

Improved Rotordynamics and Durability

The ball bearing cartridge delivers exceptional damping and control over shaft motion, allowing enhanced reliability for both everyday and extreme driving conditions. In addition, the opposed angular contact bearing cartridge eliminates the need for the thrust bearing, commonly a weak link in the turbo bearing system.

And best of all for those who wish to push the limits, ball bearing design turbochargers provide significantly higher robustness by better supporting the rotating turbocharger assembly, as well as better spreading thrust loads over old fashioned methods.

Water Cooling

Whilst turbochargers began to be applied to passenger cars in the late 1970's in response to the energy crisis, the first generation passenger car turbochargers were derived directly from commercial diesel engines. Engine oil was used to provide both lubrication and cooling and whilst this was an effective compromise between cost, durability and performance, in high engine performance applications durability suffered through fouling of the turbocharger bearings through high turbine and bearing temperatures.

By encasing the turbocharger bearings in intricate water passages, engine coolant is used to significantly reduce turbocharger bearing temperatures in order to eliminate the coking and lacquering issues that fouled old fashioned turbocharger bearings. Non water cooled turbochargers have no place in a high performance gasoline engine application and should be avoided at all costs.

The graph above shows the turbocharger bearing temperature leading up to engine shutdown and for 20 minutes following shutdown. The temperature is displayed relative to the coking threshold of high quality mineral based oil.

As is clearly evident, the old fashioned non water cooled turbocharger operates above the coking threshold when under high load and experiences a very high temperature increase through heat soak immediately after engine shutdown. The APS water cooled turbocharger on the other hand remains cooler than the coking threshold at all times and the bearing temperature increase through heat soak immediately after shutdown is reduced drastically.

By specifying the latest in turbocharger designs that incorporate both water cooling and true twin ball bearing designs, the APS turbochargers deliver bullet-proof reliability and durability along with exceptional power levels and unprecedented no-lag turbocharger response.

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