In a divided-exhaust turbocharging system, 1 exhaust valve and port from each cylinder can be directed to the turbocharger turbine (referred to as the Blowdown Path) and the other can bypass the turbocharger (referred to as the Scavenge Path). If the Blowdown and Scavenge valve events are carefully chosen, significant benefits in specific power and engine efficiency can be achieved compared to conventional coupling of a turbocharger with an engine. The ability to block the Scavenge path during cold-start was demonstrated to yield a very large improvement in catalyst warm-up. In previous publications of the Valve Event Modulated Boost (VEMB) we demonstrated that fixed Blowdown events timing combined with variable Scavenge timing, or fixed Scavenge valve events combined with variable Blowdown timing; could provide high engine efficiency due to low pumping work and low high-load Residual Gas Fraction. The variable blowdown or Scavenge timing provides modulation of engine boost without the need for a turbocharger wastegate. Variable independent Scavenge or Blowdown timing was achieved with a concentric-camshaft controlled by a cam-phaser. In this project we replaced the exhaust-side concentric-cam system with an optimized 1-piece cam, controlled by a cam-phaser and replaced the non-wastegated turbocharger with one that provides the following control functions: • Cold-start bypass • Low-speed boost enhance (“Boost Valve”) • Wastegate The performance of the engine with this system was evaluated in modeling and simulation. Performance and efficiency are compared to the base engine as well as the VEMB version of this test engine. A truly world-class performance envelope was demonstrated with this system: 90kW/L at rated power with 19.5 Bar BMEP at 1500 rpm with a single-scroll turbocharger on a 4-cylinder engine with extremely low-level of scavenging. Overall the following benefits of Divided-Exhaust with Boost Valve were demonstrated: • High specific power and torque with very low engine scavenging (exhaust O2) • Improved mid-to-high load efficiency due to lower RGF and pumping work • Cold-start catalyst light-off (same as VEMB) The DE-Boost system design has the potential to provide enhanced engine efficiency and performance along with allowing a turbocharged GDI engine to meet the new very stringent emissions standards that require very quick catalyst light-off and very low engine scavenging.