Corvette, GM Truck V8 Engines Have Much in Common
“The 6.2-liter is really a performance truck engine,” explains Jordan Lee, chief engineer on GM small-block program. “It does have some of the features of the LT1. Cylinder heads, the intake ports, valve sizes — those are all common.”
The 6.2L was one of three new EcoTec3 engines introduced yesterday during the reveal of GM’s next-generation truck platform. The lineup also includes a 5.3-liter V8 and a 4.3-liter V6. This follows GM’s October introduction of the 6.2-liter LT1 that will be the base engine in the 7th-generation 2014 Corvette. All four engines are the first members of the new Gen V small-block family.
The obvious physical difference between the Corvette and truck engines is the intake manifold.
“Airflow characteristics and tuning are different. In the Corvette we had very low intake restriction, very low exhaust back pressure,” says Lee. “In the truck engine we’re trying to get a lot of torque and power. The long intake runners really help in boosting the low-end.
“That’s our freight train, the 6.2,” continues Lee. “I can’t reveal them right now, but peak torque numbers are going to pretty much make people forget about the big block.”
Some noticeable similarities between the EcoTec3 engines include a 92mm-stroke (3.62 inches), and the 4.3L and 5.3L will have an 11.0:1 compression with the 6.2L a tick higher at 11.5:1.
“We weren’t trying to make the stroke the same but 92mm works well for both the V6 and V8,” says Lee. “We looked at the sensitivity of compression ratio on detonation under heavy loads and hot ambient temperatures. With the combustion system we’ve defined, the 6.2 will be premium fuel recommended and the other two will be regular.”
Key to the Gen V family is a strategy that optimizes traditional overhead-valve architecture with an “advanced combustion system” that includes direct injection and variable valve timing for performance, then implements cylinder deactivation — which is branded as Active Fuel Management or AFM — during light engine loads to save fuel. In the V8 engines, half of the cylinders are killed during AFM. In the V6, two cylinders are deactivated.
“The V6 was more difficult to make sure we had smooth the NVH characteristics in cylinder deactivation mode,” says Lee.
Need for balance
A 90-degree V6 configuration does require a balance shaft to counter the vibrations inherent to an engine with an odd number of cylinders in each bank. However, GM engineers were faced with packaging issues trying to fit the AFM hardware within the lifter valley. When in AFM mode, cylinders Number 3 and 6 are deactivated, or the middle cylinder on one side and the rear cylinder on the other.
The 4.3-, 5.3-liter and 6.2-liter engines have been staples in GM truck line for many years. Even with a clean sheet design in the Gen V architecture, engineers stayed with those displacements.“The 5.3 has been a sweet spot for a long time,” explains Lee. “We looked at increasing and decreasing it in a three-engine lineup it, but it seems to be the right displacement for offering the best balance between performance and fuel economy.
“The 4.3 is not only good from a truck perspective because it has enough displacement to pull a trailer, but even in four-cylinder mode there’s enough displacement to push the truck down the road,” adds Lee.
Sharp-eyed truck shoppers will note that higher-than-usual oil capacities on the EcoTec3 engines. The V6 requires six quarts while the V8s have 8-quart pans. Previous V8 engines had 6-quart capacities.
“It’s something we wanted to do for the customer,” says Lee, noting GM also integrated an oil-level sensor in the diagnostics. “We realized a lot of people just never check their oil level if running 8-to-10 thousand miles between changes. We wanted to make sure with this next generation of truck that we really protected the engine and the customer. The oil also stays cooler and cleaner while engine longevity is improved.”