My daily driver is a Hyundai Sonata with the 2.0L GDI Turbo engine. It uses a one-piece, stainless steel exhaust manifold and turbine housing. Many other new, small, GDI turbo engines also use twin scrolls - think of the new GM 2.0L GDI Turbo and the BMW N20 2.0L GDI Turbo. Others still use single scroll - such as the Ford 2.0L Ecoboost.
The description below of the twin-scroll on the Hyundai engine provides an explanation of the benefits better than I could. BTW, the Hyundai engine makes 274 hp from its 2.0L, with 17.4 psi of boost, and with 87-octane gas. Highway economy rating is 33 mpg. Really amazing, if you think about it. The zero-to-sixty on my Sonata is in the 6-second range, depending on the day and which magazine tested it. I notice very little lag - only time I feel it is when I nail the throttle from a very low speed - it takes almost as long for the tranny to downshift as it does to spool the turbo.
Twin-scroll turbocharger. The turbocharged engine features a twin-scroll turbocharger that, when combined with the GDI system, results in instantaneous power delivery. Twin-scroll turbocharger designs have two exhaust gas inlets divided by split walls inside the turbine housing, with both gas passages controlled by a waste-gate. A twin-scroll turbo recovers even more energy from the exhaust than a single-scroll turbocharger thanks to a divided manifold.
The twin-scroll design separates the cylinders whose exhaust gas pulses interfere with each other resulting in improved pressure distribution in the exhaust ports and a more efficient delivery of exhaust gas energy to the turbocharger’s turbine.
For example, at the start of the intake stroke of cylinder one, and when both the intake and exhaust valves of cylinder one are open (valve overlap period), cylinder three already starts its exhaust stroke with the exhaust valve open. If the exhaust passages of cylinder one and three were connected, the exhaust gas pulse from cylinder three would increase the back pressure of cylinder one. This would reduce the induction of the fresh air and increase the amount of hot residual gases inside the cylinder. However, with the twin-scroll turbocharger setup, this interference is minimized.
The result of this superior scavenging effect from a twin-scroll design leads to better pressure distribution in the exhaust ports and a more efficient delivery of exhaust gas energy to the turbocharger’s turbine. This in turn allows greater valve overlap, resulting in an improved quality and quantity of the air charge entering each cylinder.
With more valve overlap, the scavenging effect of the exhaust flow can literally draw more air in on the intake side. At the same time, drawing out the last of the low-pressure exhaust gases help pack each cylinder with a denser and purer air charge. Maximum boost from the turbocharger is 17.4 psi.
The twin-scroll turbocharger design has several other advantages over traditional, single-scroll turbocharging systems, Hyundai says, including:
Two key features of Hyundai’s twin-scroll turbocharger setup are:
The description below of the twin-scroll on the Hyundai engine provides an explanation of the benefits better than I could. BTW, the Hyundai engine makes 274 hp from its 2.0L, with 17.4 psi of boost, and with 87-octane gas. Highway economy rating is 33 mpg. Really amazing, if you think about it. The zero-to-sixty on my Sonata is in the 6-second range, depending on the day and which magazine tested it. I notice very little lag - only time I feel it is when I nail the throttle from a very low speed - it takes almost as long for the tranny to downshift as it does to spool the turbo.
Twin-scroll turbocharger. The turbocharged engine features a twin-scroll turbocharger that, when combined with the GDI system, results in instantaneous power delivery. Twin-scroll turbocharger designs have two exhaust gas inlets divided by split walls inside the turbine housing, with both gas passages controlled by a waste-gate. A twin-scroll turbo recovers even more energy from the exhaust than a single-scroll turbocharger thanks to a divided manifold.
The twin-scroll design separates the cylinders whose exhaust gas pulses interfere with each other resulting in improved pressure distribution in the exhaust ports and a more efficient delivery of exhaust gas energy to the turbocharger’s turbine.
For example, at the start of the intake stroke of cylinder one, and when both the intake and exhaust valves of cylinder one are open (valve overlap period), cylinder three already starts its exhaust stroke with the exhaust valve open. If the exhaust passages of cylinder one and three were connected, the exhaust gas pulse from cylinder three would increase the back pressure of cylinder one. This would reduce the induction of the fresh air and increase the amount of hot residual gases inside the cylinder. However, with the twin-scroll turbocharger setup, this interference is minimized.
The result of this superior scavenging effect from a twin-scroll design leads to better pressure distribution in the exhaust ports and a more efficient delivery of exhaust gas energy to the turbocharger’s turbine. This in turn allows greater valve overlap, resulting in an improved quality and quantity of the air charge entering each cylinder.
With more valve overlap, the scavenging effect of the exhaust flow can literally draw more air in on the intake side. At the same time, drawing out the last of the low-pressure exhaust gases help pack each cylinder with a denser and purer air charge. Maximum boost from the turbocharger is 17.4 psi.
The twin-scroll turbocharger design has several other advantages over traditional, single-scroll turbocharging systems, Hyundai says, including:
- Improved combustion efficiency;
- Low engine-speed efficiency;
- Kinetic exhaust gas energy is not wasted or trapped;
- Cooler cylinder temperatures;
- Lower exhaust temperatures;
- Leaner air/fuel ratio; and
- Better pressure distribution in the exhaust ports and more efficient delivery of exhaust gas energy to the turbocharger’s turbine.
Two key features of Hyundai’s twin-scroll turbocharger setup are:
- The stainless steel exhaust manifold and the twin-scroll turbine housing are cast in a patent pending one-piece design. Thanks to the integrated stainless-steel turbine housing with the exhaust manifold, not only is the weight and cost of the casting dramatically reduced, the durability of the turbine housing is also improved.
- The waste-gate for the turbocharger uses a motor-driven electrical controller instead of being mechanically controlled. By adapting the motor-driven electrical waste-gate, the boost pressure is precisely controlled. The back pressure is reduced when turbo boost is not necessary by opening the waste-gate, which improves fuel efficiency. In addition, during cold starts, the waste-gate remains open which results in faster catalyst light-off for reduced exhaust emissions.
