EFR Turbine Housings The EFR series uses the most premium materials and processes for the turbine housings that are currently available. The material is HK30 cast stainless steel which is extremely crack-resistant. Having OE-level durability when used in conjunction with gasoline exhaust gas temperatures means never having to give your turbine housing any worry of failure. It is truly fit for purpose whether that’s street use, road racing, or even endurance racing. Another feature of these housings is the investment casting process. This process is the same as what is used for jewelry-making, yielding intricate detail and fine surface finish. The resulting turbine housing is beautiful inside and out. On the outside, it gives a show-quality finish unlike that of a sand casting. On the inside, the turbine flow enjoys a reduction in flow friction due to the smooth surface.
The part can be easily polished if desired, and either way (as-cast or polished) has a very nice color once heat-cycled. It is naturally corrosion-resistant.
All that being said, the design of these housings is all business. There are four castings that make up the initial release of the EFR series, with more to come. The smallest three of the four are wastegated housings. Two of the four are divided (twin scroll) housings. These four castings can be trimmed for the various turbine wheel options yielding a total of 16 turbine housing combinations. These 16 combinations span a PHI range of 0.020 to 0.048 (see BorgWarner Match-Bot turbo matching tool & catalog for details) to give maximum turbine flow options.
0.64a/r Wastegated (A-Type) The A-Type housing is designed for use with our smallest wheels in the range, the 55mm and 58mm. It uses a “T25” inlet flange shape that is industry-standard for this size. The flange is very compact to the body of the housing in the sprit of making the housing easy to package especially on twin-turbo installations. This tightly-coupled flange requires the use of a manifold-mounted stud through the most confined mounting hole. This hole is closest to the wastegate port and due to the compact size makes for a tight squeeze. The stud can’t be too tall emerging from the manifold or it will interfere with the housing’s surface. The nut must be tightened during the process of lowering the housing onto the manifold. The other three are easy to access (by comparison). The housing volute has a 0.64a/r which is nicely optimized for these two smaller wheels. The wastegate port is a generous 31mm port (36mm valve head) which is significantly larger than virtually all aftermarket housings that came prior. The targeted audience is the owners of smaller “street” engines (1.6L – 2.2L) or users installing a twin-turbo system. All four EFR housings have outlet machining that is designed for use with a 3” v-band. The v-band isn’t actually 3” in diameter, but it’s the common size that is used in conjunction with 3” downpipe tubing. The joint is “half Marmon” meaning that half of the flange is on the turbine housing and the other half of the flange (the other angle) is welded to the downpipe.
0.83a/r Wastegated (B-Type) The B-Type housing is designed for the 64mm, 70mm, 74mm, and 80mm wheels. It uses a “T3” inlet flange shape that is standard for this size. The housing is the “big brother” of the A-type and is very similar in design theme, only larger. The a/r is 0.83 which is within the sweet spot for these wheels and is a balance between response and efficiency performance. The B-Type housing has a very large wastegate: 36mm port and 42mm valve head. This wastegate is truly designed for high flow, even for the big-power users. Gone are the days of needing to buy expensive and bulky external wastegates. This is a real “value” feature of the EFR program. A controversial feature of the “B” housing is the offset outlet. This outlet shortens the axial length of the housing by bringing the outlet down and towards the wastegate port. It also tightens the packaging by putting the downpipe closer to the manifold runners. It also has a functional reason: it favors the wastegate flow and makes that an ultra short and direct shot. So, what’s controversial? It looks unusual, and it appears that it would hurt turbine wheel flow. The housing has been tested with and without the outlet offset and results show that no loss results from it. Keep in mind that 30-40% of the flow is through the wastegate port during high-flow conditions.
0.92a/r Wastegated (C- Type) The C-Type housing is designed for the 58mm, 64mm, 70mm, and 74mm turbine wheels. It uses a “T4” divided inlet flange shape that is standard for this size. The a/r is 0.92 which is also within the sweet spot for these wheels. Being a twin-scroll, it is a little larger than the B-Type sibling. Higher flow is the result but the low-end response is retained (and surpassed) due to the divided nature. As discussed in a previous section, the twin-scroll housing and manifold preserves pulse energy all the way from the engine exhaust blowdown event to the turbine wheel, resulting in low-rpm boost response amplification. The C-Type housing also has a very large wastegate: 36mm port and 42mm valve head. This wastegate seals both branches of the twin-scroll volute since each volute has a wastegate channel leading to the Siamesed outlet port. The C-Type also has an outlet offset, but somewhat less than the B-Type housing.
1.05a/r Wastegated (D- Type) The D-Type housing is designed for the 64mm, 70mm, 74mm, and 80mm turbine wheels. It uses a “T4” divided inlet flange shape. The a/r is 1.05 which is on the high end of optimum and is targeted at the big-power users who want maximum flow yet still very high efficiency, especially in the pre-wastegated operating region. Like the C-Type housing, this part is divided (twin scroll) for the best combination of low-end response and top-end power. The D-Type housing is not wastegated, and as a result the outlet length is very short and without any offset. Like the others, it uses a 3” tube downpipe v-band connection.