Project FD RX7 Restomod: Part 26 – BorgWarner EFR Turbo System and TurboSmart WG

We are going to back-to-back test Borg Warner’s EFR 8374 and EFR 9180 turbos on our Bridge and Semi Peripheral Ported 13B REW engine.  The twinscroll turbo will be mounted on the Turblown Engineering Investment Cast 347SS Exhaust Manifold and boost is kept in check by twin TurboSmart CompGate40 wastegates.  Needless to say, we are very excited to see how these turbos stack up to each other on this build.

The BorgWarner EFR (Engineered For Racing) turbos were first introduced in the Verizon IndyCar series in 2012.  The game-changing low inertia “Gamma-Ti” titanium-aluminide alloy turbine wheels are half the weight of typical turbine wheels.  Combined with dual ceramic ball bearing cartridges, forged milled aluminum compressor wheels, and stainless steel Twinscroll turbine housings; the EFR turbo lineup delivers transient boost response and spool characteristics that are still competitive, relevant, and winning races over a decade later.

In that timeframe, turbo technology has made a lot of progress and changes, however, no one has developed an alloy that is similar in weight as “Gamma-Ti”, which is nearly the same weight as the forged-machined compressor wheel.  This nearly 1:1 turbine-to-compressor weight ratio is extremely hard to beat and greatly improves turbo response.

EFR turbos also feature integrated, and recirculating blow-off valves (BOV) built into the compressor housing.  This design helps to keep the turbo spooled between shifts by redirecting high-pressure air from the outlet of the compressor wheel, right into the low-pressure inlet of the turbo.  This saves a few hundred dollars due to not needing an external BOV.  Speed sensor ports and integrated boost control solenoids are also included in EFR turbos, further reducing the cost of the complete integration.

These are the reasons EFRs turbos remain so popular in the Time Attack and aftermarket industry, and are the go-to solution for most rotary builds.

The BorgWarner EFR 8374 and EFR 9180 turbos are arguably two of the most popular turbos for the RX-7’s 13B REW engine.  These two turbos share the same “B2” Turbo Frame Size and have identical external dimensions to each other.  Both turbos utilize the same castings for the turbine and compressor housings, and only the internals are machined to different dimensions for the differing wheel diameters and inlet/outlet sizes.  This will make back-to-back testing on the dyno very quick and easy, to give us a good comparison of the differences in powerband, response, and output.

There are a few different turbine housing configurations of these turbos:

B-Type: internal wastegate, 0.83 A/R, T3 flange, Single Scroll turbine.

C-Type: Internal wastegate, 0.92 A/R, T4 flange, Twin Scroll turbine.

D-Type: External wastegate, 1.05 A/R, T4 flange, Twin Scroll turbine.

H-Type: External wastegate, 1.45 A/R, T4 flange, Twin Scroll turbine. (used in Indycar).