Ecotec Tech

Over the years, GM’s Ecotec line of engines has by and large been seen as nothing more than an economical and reliable underhood offering. But with its “Gen II” revision that debuted with the 2.4L LE5 engine, GM drew upon experience racing the Ecotec engine family and built in strength to handle extra horsepower, with thickness being added to the main bearing bulkheads, cylinder bore walls, and other areas. The stage was set for a badass, forced-induction four-banger, and here we have it with the turbocharged, 260hp 2.0-liter known as the LNF.

Built for toughness, the LNF features a steel crankshaft and forged connecting rods. The pistons, while of a cast aluminum variety, feature a built-in oil galley and nifty jet-spray cooling system. We spoke to GM’s Ed Groff, Assistant Chief Engineer for the LNF engine program, about this and other aspects of the design. “During development, we attached thermocouples to the pistons to allow us to analyze temperatures while the engine was in operation. Piston temperatures are a function of power level, and based on what we saw initially we decided that for the 260hp target power level, we were closer to our in-house limit than we wanted to be. This jet spray technology allows us to cool the piston by between 40 and 50 degrees C (104-122 degrees F), opening up a large safety margin for the engine.”

Saturn Sky Redline Rear Right
Exterior details for the Red Line include dual exhaust outlets, TURBO badging, and a more aggressive front fascia with revised grille openings.
For power, this DOHC engine features variable valve timing on both the intake and exhaust, and a “dual-scroll” turbocharger that delivers 20 psi of boost with minimal lag. This is achieved through some pretty badass technology. “We separate the exhaust passages of cylinders 1 and 4 from those of cylinders 2 and 3 all the way from the exhaust ports to where they enter the turbocharger,” says Groff. “So you actually have two nozzles feeding the turbine wheel; hence the term dual-scroll. This creates somewhat stronger exhaust pulses as different cylinders are not interfering with one another as the engine goes through its firing order, which helps the turbine. Also, going off of conventional four-cylinder tuning during the valve overlap period, the cylinders are not experiencing pressure pulses coming back from the exhaust. Because of the combination of the dual-scroll and the VVT, we are able to design in a lot of valve overlap at low engine speed, which helps low-end torque.”

But the real story on the LNF is gasoline direct injection, the first system of its kind offered in North America by GM. Instead of squirting fuel into the intake port upstream of the intake valves, fuel is instead injected directly into the cylinder during the intake stroke––at an amazing pressure of up to 2,250 psi. This results in superior fuel atomization and a more efficient burn. To accommodate such a SIDI (Spark Ignition Direct Injection) system, a special intake manifold, cylinder head, high-pressure mechanical fuel pump, and variable-pressure fuel rail are used. The SIDI system pays many dividends, including allowing a higher compression ratio as well as a leaner air/fuel mixture.

Also noteworthy for the LNF-equipped Sky is that fuel efficiency is improved over the 2.4L model, with an estimated 21 city/30 highway with the manual tranny versus the standard model’s 20/28. Although clearly this difference has to do in part with the 0.4-L decrease in displacement and efficient direct injection system on the Red Line’s engine, it probably is also due to the fact that GM engineers cut the final drive ratio from 3.91 to 3.73 for the car’s turbo version. The two models share similar axle assemblies borrowed from the Sigma platform (CTS-V), so this is at least encouraging news for Red Line owners looking to swap to a lower final drive ratio for quicker acceleration. This turbocharged 2.0L mill will also be used in the 2007 Solstice GXP and Opel GT. And as if 260 hp isn’t enough, look for substantial power increases on this engine in model years to come!