It's one of the most highly anticipated engines of the last five years, with a lineage that goes back more than half a century. Although critics and pundits have been repeating the mantra "pushrods are dead" for about half the small-block's life, the all-new fifth-generation small-block triumphantly debuts with the same traditional valvetrain it's had for its whole life. But this is no low-tech lump. The new LT1 V-8, which will debut in the 2014 Chevrolet Corvette, features a veritable laundry list of state-of-the-art technologies. Different displacements and variations of the LT1 will be the basis of the bread-and-butter V-8s that will power the 2014 Chevrolet Silverado and GMC Sierra trucks when they debut.
Same Size, More Power, More Efficiency Early on, there was some speculation that the production C7 Corvette's engine would be downsized to 5.5 liters, as it was for the C6-R in the American Le Mans Series to meet class displacement rules. That speculation has now been officially debunked, as the LT1 is a 6.2-liter, just as its predecessor LS3 was. Traditionally, large displacement has been synonymous with high fuel consumption, but the LT1's size actually works to its advantage, thanks to the application of GM's Active Fuel Management, the company's house brand for cylinder deactivation.
Because the engine makes enough power in four-cylinder mode for a lot of light-load driving, it can operate in V-4 mode longer than it could with a smaller-displacement, lower-torque engine. Preliminary projections for fuel economy for the C7 are up to 26 mpg highway. One of the other key enabling technologies for this remarkable level of efficiency is direct fuel injection, something that had been rumored for a long time, and was officially confirmed by GM in December 2011.
Of course, efficiency and technology are all well and good, but especially in the context of the Corvette, it has to perform. And with "at least" 450 hp and 450 lb-ft of torque, the new LT1 is expected to rocket the C7 from 0-60 in less than 4 seconds. With different tuning and displacements, the Silverado probably won't be quite as fleet, but it's encouraging that this powerhouse is the basis for the next-generation truck powerplants.
Durability was a key consideration in the development of the LT1, and as important a factor as it is in a sports car, it's even more critical in the context of a truck. With more than 6 million hours of computer analysis, and the equivalent testing time of going around the world 60 times, this engine is built to perform under all conditions, even being repeatedly cycled from below freezing to 239 F repeatedly while running at peak power.
Some thought the fifth-generation small-block would debut with a version of Chrysler's concentric cam concept as employed on the SRT Viper, allowing for independent variability of intake and exhaust timing. At least at its debut, the LT1 employs parallel cam phasing, with the intake and exhaust timing advanced or retarded concurrently. And for those skeptics who think pushrod engines are choked for airflow, massive clarinet-size 55mm intake valves and 40.4mm exhaust valves ensure the LT1 can breathe deeply. A high 11.5:1 compression ratio helps the engine deliver healthy low-end torque, sharp throttle response, and complete combustion. For durability and lower-octane usage, expect the truck powerplants to have a slightly lower compression ratio.
Just as the LS1 did in 1997, the LT1 previews many of the features and technologies that will be employed on the more mainstream, higher-volume truck powerplants. Since the displacement carries over on the LT1, we're fully expecting 5.3 and 6.2 liter versions for trucks. We're a little less sure about the 4.8, as it typically sells in lower volumes than the 5.3, and the big mystery is the base engine in the trucks. Speculation is running about 50/50 right now whether the high-feature DOHC 3.6 V-6 will be the base engine in trucks, or if an all-new 4.3-liter V-6 based on the Gen V small block will appear.
We believe GM is low-balling the power gains on the LT1, considering the specifications on the engine. The claimed 450 hp for the LT1 is about a 5 percent improvement, but we think final production numbers will be closer to 10 percent, and believe the power gains for the truck powerplants could be similar. Indeed, if GM wants to be even with Ford, a 10 percent gain for the 5.3 is practically mandatory, as the Ford 5.0L DOHC V-8 holds a 40-hp advantage over the current GM 5.3, with the 3.5 EcoBoost V-6 widening the gap to 45 hp.
But equally important to truck customers is fuel efficiency, and with the current 5.3-liter Vortec V-8 coming within a whisker of matching the EcoBoost's fuel efficiency, you can bet GM is designing the truck engines to offer class-leading V-8 fuel economy, possibly even surpassing the EcoBoost in EPA ratings, and you can bet the General will shout it loudly and proudly if it does. Power and torque figures in the neighborhood of 350/360 for the new Gen V 5.3L is what we're putting our money on, give or take a few ponies & pound-feet.