The BorgWarner EFR series is a combination of all the leading edge technology available today. On such combination is there aerodynamics of which inducing the compressor technology known as Extended Tip Technology. There are six compressor wheel sizes within the EFR product range. 62mm, 67mm, 70mm, 76mm, 83mm, and 91mm. The two smallest wheels (62mm and 67mm) offer very large map width while still enabling high-boost operation. Very important for small engines striving for peak torque at streetable engine speeds, these compressors offer surge line positions that are far to the left on the map without needing a cover recirculation slot and cavity. The wheel itself is designed to not need an inducer recirculation slot, but furthermore it helps solve packaging problems due to the 2.5” inlet hose connection. Through a high backsweep angle on the blade outlet and our Extended Tip Technology on the exducer tip, these wheels offer excellent range (flow capacity) while still being capable of high boost at reliable turbo speeds. Both the 62mm wheel and 67mm wheel employ a large 80% inducer trim (64% on an area basis).
The rest of the compressor wheels (70mm through 91mm) are of a different design. These Extended Tip Technology wheels are very unique in that they are our highest-boost capable wheels but still give outstanding map width and flow capacity. The compressor cover treatment includes an inlet recirculation groove for maximum width and anti-surge characteristics. A new trim set was developed for this program on these wheels, which is 75% trim (56% on an area basis). This large trim gives up a very small amount of efficiency but for a significant gain in flow capacity. The only trim exception is the 91mm version. This part is released at 74% trim as to maintain an inducer diameter that is compliant to some specific drag racing class rules.
The EFR product line features compressors ranging from 62mm OD (~50mm inducer) to 91mm OD (~68mm inducer). From this, the 70mm through 91mm compressors are designed for high-boost (30+ psi) capability. The smaller 62mm and 67mm wheels are from a different design family, used for “medium” boost but very large flow range. Due to their small size, paired with other technologies like the Gamma-Ti turbine and ball bearing system it yields an extremely responsive system specifically targeted at small engines or twin-turbo installations.
The material chosen for all 6 compressor wheel sizes is forged aluminum, fully milled. Also known as “billet”, these wheels are as amazing in appearance as they are in function. Cut from custom forgings, their strength exceeds that which is available from typical bar-stock and also exceeds the material properties of an aluminum casting.
The 62mm and 67mm wheels feature an 80% diameter trim (64% on an area basis), giving them a very high-flow characteristic. They are uniquely capable of having this trim while still having acceptable stress levels, blade frequencies, and boosting capability. The 70mm, 76mm, and 83mm wheels have 75% diameter trim (56% on an area basis) which gives them optimized flow, strength, and high boost capability. The 91mm wheel is trimmed slightly smaller (74% diameter; 55% area) to fit within some specific drag racing class rules.
All six EFR wheels feature our Extended Tip Technology. Just as on the S200SX, S300SX, S400SX, and S500SX lines, this feature amplifies the boost pressure and flow capabilities for a given wheel size. This BorgWarner feature has been a segment-leading technology for many years and it is continued here with the EFR series.
We investigated the use of an abradable coating on the compressor cover and got mixed results. Sometimes it yielded an efficiency and boost pressure gain but other times it did not. It also had mixed effects during the startup and cut-in process; effects that are all in need of further study. This feature will continued to be evaluated by the BW team and might be released at a future date either on EFR or Airwerks products, or perhaps both.
Three all-new compressor cover castings have been created for the EFR product line. For the purposes of this text, let’s call them “A”, “B” and “C”. All three have some common features: First, they are retained to the bearing housing with a v-band which helps for easy orientation adjustment. Second, they have intregrated CRV (Compressor Recirculation Valve) ports and mounting. Third, they provide a mounting pad for the boost control solenoid valve (BCSV).
“A” Compressor Cover
This casting is used with the 62mm and 67mm compressor wheels and has a compact non-recirc inlet size. Designed for smaller packaging spaces, a 2.5” inlet hose connection is used. The outlet is machined for a 2” hose connection. As mentioned above, the CRV and BCSV mounting features are included. The volute a/r is 0.46.
“B” Compressor Cover
This casting is used with the 70mm and 76mm compressor wheels and features a recirculation (“recirc”) groove. This groove surrounds the leading edge of the compressor wheel and provides an escape path for air on the tip of the wheel. In the process, the surge margin is extended when operating on the left side of the compressor map. On the right side of the map the operating range is also extended. In this zone, air is admitted through the port and into the wheel. The function of the recirc groove is very different than that of the CRV. The recirc groove is in operation all the time. The CRV operates only during a throttle-closing event and helps prevent compressor backflow and related compressor surging. The inlet connection on this cover is sized for a 3.5” hose and the outlet is for 2” hose. Otherwise, it’s very similar in size and shape to the small cover. Again, the CRV and BCSV features are integrated. The volute a/r is 0.5.
“C” Compressor Cover
This casting is used with the 83mm and 91mm compressors and also features a recirc groove and cavity. Due to the larger size wheel bore, a 4” hose connection is used. The outlet connection is also larger, being sized for a 2.5” hose ID. This outlet is unique because it can also be modified for a v-band connection. The hose connection can be cut off and then a hard-mount piece (such as an elbow or tube assembly) can be clamped on. The 0.57 a/r volute shape of this cover is one of our long-time staples, having been also used in our popular S300SX and S400SX lines. Again, the CRV and BSCV mounting features are integrated.
09
Dec 2012