Clamp Plate Flexibility
Since the EFR compressors use a v-band to hold the compressor housing onto the backplate, there are no compressor housing clamps. While it gives the turbo a commercial diesel look (my opinion), it does give the installer a super quick way to re-clock the compressor housing. On turbos that use clamp plates to hold the turbine housing to the center section, they're almost always a bitch and a half to work on either because of water or oil fittings getting in the way or corrosion and bolt fatigue (in the case of a used turbo). Another ingenious feature of the BW EFR turbos are clamp plates that rotate out of the way. I LOVE THIS FEATURE ALSO. This makes life about 15000x easier in custom applications where you need to re-clock housings or need to service something regularly that requires turbo removal.
You only need to rotate the plates and tighten the bolts to clamp the turbine housing to the center housing. There are no difficult to work with multiple plate bolts that require complete bolt removal for plate and housing removal.
Aerodynamic Wheel Designs
EFR compressor and turbine wheels are designed using modern aerodynamics. Some of the wheels are similar to the BW Airwerks line of turbos, but all of the EFR compressor wheels are forged and milled. If you take a look at the compressor maps, don't be surprised that you're looking at a map of a compressor section with a compressor wheel that is substantially smaller than the competitor's. As an example, the EFR8391 turbo's compressor wheel is capable of flowing 95lb/minute of air, but only has a 67.3mm inducer and a 91mm exducer. That's actually pretty small for a compressor capable of such high flow. Compare it with this turbo's compressor map which has a 74.7mm inducer and a 102.3mm exducer.
The EFR compressor maps all have one thing in common: they are ultra wide, high pressure ratios, and have very wide efficiency islands which are all really good things.
Drawbacks to EFR
There's no way in hell you can have your cake and eat it too. The world doesn't quite work that way. The one major drawback for you guys looking to retrofit an EFR turbo in to an existing fitment, is you'll find that the Series EFR turbos are unlikely to directly retrofit into existing T25/28, T3/T4, or GT30/35/40/42 fitments. This is great for manifold suppliers like Full Race who are another one of BW's testing partners. Since the EFR turbos are so highly optimized, the turbos occupy a slightly larger envelope. While there's probably not going to be any issues in race cars and rear wheel drive cars, I can see some potential difficulties fitting EFR turbos in transverse, front turbo engines (e.g. Honda B/D/H series, SR20 FWD, etc.). This would be especially true where A/C, power steering pumps, engine mounts, bellhousings, or radiator fans could prevent EFR turbo fitment.
Another possible drawback is that the turbine housings are not available in various A/R sizes due to specific gas flow optimization for the housing and wheel shapes. It is possible that BW may release other A/Rs in the future, but for now the T25 inlet wastegated housing is only available in 0.68a/r, the T3 open volute (single entry) wastegated housing is only available in 0.85a/r, the T4 divided (twin scroll) wastegated housing is only available in 0.95a/r, and the T4 divided (twin scroll) non-wastegated housing is only available in 1.05a/r. If you are designing your turbo system from scratch, the BW turbine housing and wheels selections allow for nearly infinite increments of gas flow, BUT if you are stuck with an existing installation (e.g. T3 flanged exhaust manifold that you wanted more top end power on) then you would not have any other a/r choices. The positive side to all this is that with such a low inertia turbine wheel and high efficiency turbine stages, you may find that the 0.85a/r housing will do just fine and possibly even respond better than whatever you had before that might have been a smaller A/R.
Look on BorgWarner's EFR site or the Cosworth USA site soon for details like drawings and dimensions.
All in all, quite an impressive feature set isn't it? The guys at Cosworth and I will be continuing to work with EFR turbos so I'm sure there will be an update in the future. Be sure to follow MotoIQ for updates soon!