GM's highly evolved LNF engine, which is the 2.0L Turbocharged motor found in the Saturn SKY Red Line and the Pontiac Solstice GXP, just grew in stature a bit within the broader GM enthusiast community.

As many people know, I began my tuning career working with earlier generation Ecotech engines found on Chevy Cobalts and Saturn Ions before I began working with SKYs and Solstices.  For the Cobalt community, the performance engine option offered by the factory was the LSJ, a close cousin to Sky/Solstice engine that was "super"-charged instead of turbo-charged.  However, GM recently annouced the retirement of the LSJ, although they didn't leave GM enthusiasts much time to grieve before that short lived motor was quickly replaced with the turbocharged LNF.

With the high performance GXP / Red Line 2.0L Ecotec engine comes several more capabilities, but does it truly address all of the issues with the previous motor, or are there still some naggine problems?  In my evaluation, there are a lot of obvious changes to the appearance of the new LNF compared to the LSJ, but there are also a lot of changes that cannot be seen from the engine compartment which deserve more detailed analysis (and appreciation).

So what’s new? The engineers have reduced cylinder compression to allow the motor to run more boost than the supercharged version was capable of. The cams were also redesigned to be more accommodating to boost thanks to the addition of continuously variable valve timing. The variable valve timing allows the motor to phase the camshafts, opening the valves farther and for more duration during higher boost levels. In order to insure that the fuel is delivered more consistently with the demands of the higher boost levels direct injection was added. The direct injection places the fuel injector inside of the combustion chamber, like a spark plug, rather than above the valves where fuel can condense or remain after the valves have closed. The direct injection will mean that every drop of fuel that is sprayed goes directly into the cylinder. By having the fuel spray inside the combustion chamber the motor is able to use less fuel to achieve a consistent air-fuel ratio. This will also result in cleaner valves since there will be no buildup of fuel deposits in the top side of the cylinder head. GM has also deepened the water jackets within the new block which should provide marginally better cooling efficiency and more heat dissipation thanks to freer flowing coolant.

There was also some technology carried over from the LSJ that will still be used in the LNF. The most important piece of retained technology is the Oil Sprayers which place a high pressure oil-jet directly underneath the piston to maintain proper lubrication during high RPMs, and to help cool the piston by delivering a constant stream of oil to attract heat away from the piston itself. GM also retained the Forged Steel Crank shaft and Connecting Rods, which make the bottom end of the motor capable of more horsepower than the stock turbocharger can deliver.

 The unfortunate decision that was carried over from the LSJ is the use of cast pistons. It is unclear why the designers would invest money in using forged internal components, and then place cheaper and comparatively weak pistons in the motor. The reason behind this limitation is that the cast pistons naturally have flaws in them, and the metal is also weaker. As with the previous motor, it is expected that these pistons will limit the potential of the motor to only 40% more than stock power levels. This should not be a problem for the typical car owner, but those who wish to really push their cars to the limits will be held back.

With all of these changes, you might be thinking about the real world advantages of the LNF, and what these technical differences mean. Essentially the motor is going to produce more boost with the turbocharger which results in more horsepower. The more boost you add the more air and fuel is held in the cylinder, creating the equivalent explosion of a significantly larger motor. By switching over to the twin-scroll turbocharger from the previous supercharger, the motor will still produce the immediate torque that the supercharger delivered, but the turbo will not create parasitic loss like the supercharger did. Basically the supercharger robbed the motor of about 10% of its top end power due to the physical strain required to turn the rotors of the supercharger itself. The turbocharger takes away virtually no horsepower to operate, since it is powered by exhaust gas pressures, and not the engine accessory belt. Additionally since most of the turbocharger functions are controlled by the engine’s computer, the LNF will be tunable for significantly more horsepower without the need to modify the motor itself.

With all of the tuning possibilities just over the horizon for the Solstice GXP and Sky Redline there is bound to be a lot more to offer. I have been studying the tune from the LNF, and I see a lot of areas that can be modified for increased performance. Keep your eyes out for my upcoming article on tuning the Turbocharged Solstice where I’ll be sure to let you know what we really have to look forward to.