hyundai-24-theta-gdi

Of all the GEMA manufacturers, the Hyundai-Kia Group has been setting the best track record in terms of extracting the most power and torque out of their engines. The current generation Sonata and Optima’s 2.0 litre GEMA engine (Hyundai calls them Theta, Mitsubishi calls them 4B11, etc) currently makes around 158 PS to 163 PS, which is probably one of the best in class when you’re talking about a regular engine with only variable valve timing and conventional port injection. The new “Passat CC-ish” Hyundai Sonata‘s 2.0 litre Theta II engine makes even more power, now rated at 165 PS at 6,200rpm and 198Nm of torque at 4,600rpm.

Hyundai is now taking the bar higher with the 2.4 litre engine option for the new Sonata. The 2.4 litre Theta II with variable valve timing on both the intake and exhaust now gains GDI gasoline direct injection and as a result, can produce 201 PS at 6,300rpm and 250Nm of torque at 4,250rpm. That’s some very good torque figures for a 2.4 litre engine.

Thanks to the lean burn precision that direct injection affords, compression ratio has been increased to 11.3:1. The engine also comes with a three-stake variable induction system. The variable valve timing system has also been improved, with a new drive system designed for silent operation and better durability. The block has also been reinforced, with improvements to the crank and piston design as well. For example, the piston now has a cooling jet under the piston crowd to get more oil onto the piston walls, helping reduce friction and improve economy/power.

Hyundai says conventional port fuel injection is limited in the sense that as the engine spins faster in terms of RPM, valve opening and closing times get shorter and shorter, reducing the time available for the injectors to injet fuel. A DI injector positioned inside the combustion chamber can inject fuel at pressures at up to 150 bar faster. The fuel travel path is also shorter and more direct, thus more control is available over the combustion process.

The Hyundai GDI system does injection in two phases. The first phase is called the pilot injection and ignition, which triggers the piston’s downward stroke. Then during the piston’s descent more fuel is injected and ignited. Hyundai claims this split-injection technique reduces load on the catalytic converter and helps reduce emissions. Optimal operating temperature for the cat is also achieve faster, which means better cold start emissions, a figure which Hyundai claims have improved by 25 percent.

The new 2.4 litre Theta II GDI engine will be available in the new Hyundai Sonata along with the high-powered 2.0 litre engine. No news yet when Sime Darby is bringing the new Sonata into Malaysia, but perhaps it might change people’s perception of Korean D-segment vehicles. Hyundai has also unveiled a 2.0 litre GDI Turbo engine before this.