11/05/2020
VF58's ๐ง๐ถ๐๐ฎ๐ป๐ถ๐๐บ ๐๐น๐๐บ๐ถ๐ป๐ถ๐ฑ๐ฒ (๐ง๐ถ๐๐น ๐ฎ๐ธ๐ฎ ๐๐ฎ๐บ๐บ๐ฎ-๐ง๐ถ) 9-blade Turbine Wheel & Shaft. The lighter alloy & reduced blade count improves turbine efficiency & aerodynamics for better spool, response, flow, reduced backpressure at high RPMs & overall power output.
What makes this so special?
This is the same alloy that BorgWarner uses for their EFR turbos. It was only used by Subaru in a handful of exclusive IHI turbos (eg VF36, VF38, VF42, VF56, VF58). The same technology was also implemented in the Ferrari 488's IHI turbos! And can even be found inside of some jet engines due to its reduced rotational inertia and durability at high temperatures.
TiAl is an intermetallic compound and has a specific gravity of ~4.0 g/cm^3 while Inconel 713c is ~7.9. For a given wheel dimension, that means that the TiAl wheel will have half the mass resulting in much lower spool latency. "Spool" isn't synonymous with "Boost Threshold" (Time vs RPM). These are commonly confused and used interchangeably. The lightweight and high-temperature strength properties of TiAl alloy make it perfect turbochargers and jet engines!
BorgWarner:
"The most exciting technology in the EFR package is the turbine wheel material. EFR turbine wheels are made from titanium aluminide. Itโs not the first time this material has been used, but itโs the first time that it has been offered to the public across a range of size options. Titanium aluminide (or Gamma-Ti) is a strange compound. One of those nice examples of the result being greater than the sum of the parts; this compound has temperature capability far in excess of aluminum and titanium as individual elements. The Gamma-Ti turbine wheels will gain ductility with temperature and they are extremely light. This combination results in a very durable turbine wheel. Very difficult to cast, this compound is actually an inter-metallic which means that itโs not quite ceramic and not quite metal. One major delivery of this project has been to commercialize this material to be able to introduce it at an acceptable price point. The technical advantage is very simple: low inertia. Since Gamma-Ti has roughly one-half the weight of a typical inconel turbine wheel, the reduction in inertia is substantial especially on the larger wheel sizes such as 64mm and above. The turbine wheel is so light, it is very nearly the same weight as the compressor wheel that is on the other end of the shaft. When you feel one of these parts in your hand, itโs hard to believe itโs a turbine wheel. Then you drive the car and you feel whatโs been accomplished. When paired with the ball bearing system, it yields a turbocharger that has no rivals in terms of boost response. Gamma-Ti is typically reserved for ultra-high-end turbochargers used for extreme racing or other niche markets."
Ferrari & IHI:
"Ferrari has partnered with IHI, a Japanese master in the art of turbocharging, to supply its turbochargers. Ferrari told IHI it wanted to deliver a turbocharged engine that was both powerful and responsive. IHI responded by developing one of the most technologically advanced turbochargers available in a road car.
For example, instead of using Inconel nickel-chromium alloy for the turbine impeller, a low-density titanium aluminide material (TiAl) is used; an alloy of titanium and aluminium โ two of the lightest metals used in automotive engineering. Material costs are higher, but rotational inertia is reduced by more than 30 percent. The impeller itself is also fully machined, rather than cast. The turbine shafts are mounted on ball bearings instead of the usual metal journal bearings. The compressor wheel fits snugly in the housing thanks to an abrade-able polymer seal that self adjusts as the turbo breaks-in and wears. This increases efficiency by 2 percent by maintaining a tighter seal over the life of the engine.
Normal sports cars have just one or two technologies such as these. Ferrari integrates them all to show how committed the company has been to achieving turbocharger perfection. It's also why it chose IHI to develop the unit: it knew the firm would be up to the job.
The Ferrari 488 utilizes two of these IHI turbochargers for its twin (parallel) ball-bearing twin-scroll configuration."
SUBARU TECNICA INTERNATIONALl Subaru of America, Inc.
