The new series of turbochargers just launched by BorgWarner, appropriately named EFR (Engineered For Racing), have truly changed what one should expect from a turbo. The performance advantage is so great that turbocharging leaders like Full-Race are designing all of their new manifolds to support EFR turbos.
So what makes the EFR turbo so special? A clean-slate design, which included giving free reign to BorgWarner’s top turbo engineers to develop a no-compromise performance series of turbochargers, that’s what. In fact, the same guys who designed the variable vane turbos standard on all Porsche 997 Turbos are responsible for the EFR’s design, with some very exciting new technology resulting from the process.
One of the game-changing technologies integrated in the EFR series of turbochargers is Gamma-Ti, which consists of using a titanium alloy to manufacture the turbine wheel. The advantage here is a substantially lighter turbine wheel, approximately half the density of a comparable Inconel wheel, which results in reduced inertia and greatly improved transient response or spool. The particular alloy used actually provides increased material properties at elevated temperatures, which means it provides excellent reliability in this harsh, high-temperature environment. Though Gamma Ti presented some challenges in manufacturing and assembly, the extensive research and development including ruthless lab testing performed by BorgWarner made it a reality. Finally, the Gamma-Ti turbine wheels were coupled with top-notch aerodynamics, permitting increased rotational speeds.
The Turbine housings are manufactured from investment-cast stainless steel, a new approach that also presented some manufacturing obstacles, since a twin-scroll turbine housing with optional internal wastegates is a rather complex shape. However, the end result is a housing that can withstand higher temperatures while offering an extremely smooth internal flow channel (comparable to a ported, polished, extrude honed cast-iron housing). This high-grade casting also allowed the BorgWarner engineers to reduce the wall thickness of the housing, providing some meaningful weight reduction and more rapid cooling. The stainless housing also means no rust and a cleaner-looking engine bay.
The water-cooled centersection features a dual-row ceramic ball bearing cartridge, a design that has proven to offer a substantial reduction in friction at low turbo speeds when compared with a conventional journal bearing centersection. This further aids turbo response while also improving fuel economy, making it one of those rare double-win situations where you can make your car both greener and faster. Meanwhile, a dual seal system keeps the oil in the centersection and makes sure exhaust gases are kept in the turbine housing, ensuring that crankcase pressure and contamination is minimized. BorgWarner’s EFR turbos also mean that the days of the smoky turbo are gone, thanks to the oil feed having the correct oil metering orifice built in and the oil return tapped for 3/8 NPT, while featuring the conventional flange to ease installation.
The compressor side of the EFR turbo is also jam-packed with new technology, starting with a forged milled compressor wheel offering increased strength compared to conventional cast compressor wheels. Also included are a built in recirculating blow-off valve, boost control solenoid, compressor outlet compatible with coupler (or V-band) and built-in mounting for a rotational speed sensor so you can monitor your turbo’s operation.
Now that it’s clear why the EFR is the turbo of choice for our S2000, it’s time to explain how we chose the right model for our application. Our first stop was at the BorgWarner Internet-based Match-Bot software at borgwarnerboosted.com. This software requires your specific engine parameters such as volumetric efficiency. Some web searching revealed a SAE (Society of Automotive Engineers) paper that measured the VE of an S2000 engine, so we ordered it up and entered the data in the Match-Bot software. There are multiple parameters required to determine the correct turbo match for your application, but BorgWarner has released a four-part tutorial on YouTube explaining exactly how to use it.
After following the tutorials and trying multiple iterations, we arrived at the EFR 8374 with a 1.05 A/R divided turbine housing (this particular housing is only available for use with external wastegates). The 83 represents an 83mm compressor wheel outer diameter, and the 74 a 74mm turbine wheel outer diameter. In order to maintain efficiency and our target 25 psi of boost pressure in the upper rpm range, we had to select a larger compressor wheel that is less than ideal at lower rpm. You can see that our 2000 rpm (3 psi) and 3300 rpm (7 psi) points are off the map, reducing efficiency and landing in the gray area that depicts surge. However, because this application is track only/time attack, it will rarely see low rpm and an efficient operating range from 4400 rpm to 8500 rpm is considerably more important. For street application or lower-horsepower targets, the 76mm compressor housing would have been an excellent choice.
With the turbo selection complete, we began fitment. The EFR turbo mated perfectly with our Full-Race manifold. Charge piping has been TIG-welded and constructed from Vibrant Performance’s lightweight aluminum 2.5-inch mandrel-bent tubing, coupled with its VanJen clamps. We fabricated some plastic spacers to place between the VanJen weld fittings to ensure they were kept in the middle of their travel range during fabrication. With the couplers installed, the charge pipes are able to withstand expansion/contraction of the plumbing and misalignment as a result of engine movement without binding. The integrated blow-off valve sped up installation and offers all of the benefits of a recirculating valve without the extra plumbing or space requirements. There are aftermarket options to vent to atmosphere, if you must have that pshhhh sound, but we much prefer directing the wasted boost back to the compressor wheel in hopes of improved response.
The EFR series turbos have generated substantial excitement, and understandably so. We can’t wait to get ours on the dyno and see how it performs. Stay tuned for our next installment where we fit a completely new aero package it’s wider, produces more downforce and will be the first in North America. Don’t miss it!