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

Choosing an exhaust manifold is a very important decision for the rotary engine due to the extreme heat and stress that is put on it.  It is much harder to design a reliable exhaust manifold for a rotary than it is for a piston engine.  Because of this, it is common for tubular exhaust manifolds to crack over time though all of the heat cycles.

Turblown Engineering (the Rotary-specific side of TurboSource) took this challenge and developed the Ultimate FD3S Turbo Manifold that is Investment Cast from 347 Stainless Steel.  Eliminating the welds of a tubular exhaust greatly improved the durability and longevity of the exhaust, as well as improving on the flow characteristics with tapered runners and higher flow transitions than what is possible with tubular manifolds.

347 Stainless Steel (SS) is far superior to 304 Stainless not only by lasting longer at extreme temperatures, but eliminating the welds which is where almost every turbo manifold fails at.  Being investment cast means that the Turblown manifolds are less than half the thickness of a traditional cast iron turbo manifold.  Due to having less material, they do not retain as much heat as cast iron manifolds.  Therefore, there are zero downsides to this casting process compared to welded manifolds.

The runners are tapered down to the T4 flange, which is not possible with a traditional welded manifold.  This tapering is identical to the volute of a turbine housing, increasing velocity and speeding up exhaust flow and increasing boost response.

We bolted the BorgWarner EFR 8374 turbo to the Turblown Investment Cast 347SS T4 Twinscroll FD3S Turbo Manifold to check out the fitment.

The EFR turbo is quite large compared to the size of the 13B rotary “keg” itself.

Turblown Engineering also offers their V2 Cast IWG EFR Turbo Manifold designed for internally-gated turbos.  This option makes for a very simple turbo installation and exhaust requirements since the EFR turbo is self-contained with integrated wastegates and blow-off valves.

The V2 Cast IWG EFR Turbo Manifold mounts the turbo much lower in the engine bay.  We decided on going with an externally-gated EFR which has a larger A/R and high-rpm flow characteristics, which will better suit our needs.