Truly new Corvette engines only come along once in a great while, chiefly because each basic design is so good to begin with. The original small-block Chevy architecture survived, largely unchanged, from 1955 through 1996, while various members of the advanced LS engine family powered the brand's flagship sports car from 1997 through 2013.
Clearly, then, it takes a special mill to get the nod for Corvette duty, and the Stingray's new LT1—with its direct injection, Active Fuel Management, and 460-horsepower output rating—is no exception.
To find out what makes this next-generation Vette motor run, we spoke with Small Block Chief Engineer Jordan Lee. In the discussion that followed, Lee touched on topics ranging from efficiency and performance to the future of Corvette engine technology.
Even though the Stingray uses an all-new "Gen V" engine design, you retained the LS3's 6.2L displacement. Is there something special about that engine size?
We're very scientific when we pick our displacements, just as we were with Gen IV. We do that based on the bore size we need, the power targets we're looking for, and the torque we need for driveability. All of our analysis work showed that 6.2 [liters] really is an ideal displacement.
The other thing that's really important is that, now that we have Active Fuel Management, we wanted to make sure that we had a lot of torque in four-cylinder mode. The engine will stay in that mode until the torque request you make with your right foot exceeds its ability to provide it. The LT1 makes about 230 foot-pounds of torque in four-cylinder mode, which allows you to cruise at 80 mph on the highway.
Did you have any specific performance or efficiency bogeys—a minimum horsepower or highway-mpg number, for example—for the LT1?
We absolutely did. Within reason, we want every next-generation engine to have better power, better torque, and better fuel economy. Again, it's very scientific. We start with how fast we want the vehicle to be. Tadge [Juechter, Corvette Chief Engineer] starts the ball rolling, and, in particular, he looks at zero to 60 and quarter-mile. When you take those requirements, and you know what the vehicle mass is going to be, along with the width of the tires, you can figure out how much horsepower you need. And in this instance, the target for the LT1 from day one was 450 horsepower.
So that was our goal, and we designed everything—the cylinder heads, camshaft, compression ratio, and airflow characteristics—to create an engine that makes that much power. We actually overachieved, hitting 460 with the performance exhaust system.
Fuel economy is a little bit different. We have very stringent standards to meet, both for CAFE and at a corporate level. When we translate that into engine specifics, we go back to a variable we call brake-specific fuel consumption, or BSFC. We look at certain benchmarks, including competitors' engines...primarily to see how much fuel is used at a certain load. In every instance the Gen V is better—significantly better—than the competition.
The industry standard [looks at] the amount of fuel the engine requires at 2,000 rpm with 2 bar of load. The best engines in the world are running at around 340 grams per kilowatt hour. The LT1 runs at about 330 in eight-cylinder mode, and 275 in four-cylinder mode. A smaller, 1.4-liter four-cylinder engine would be up around 340. If you look at the population of all modern engines, most of them are running at around 350 to 360.
That translates really well into the real world. I recently drove a C7 down to Charleston, South Carolina, and I had some stints where I was getting over 34 mpg. The average of the entire 1,800-mile trip was over 29.7 mpg.
Obviously not everyone buying a Corvette is doing it for the fuel economy, but we consider it a nice fringe benefit.
Was an overhead-cam configuration ever considered? If so, why wasn't it pursued?
Yes, we tried to be as objective as possible. Since this was an all-new car, we looked at all types of powertrain options that would allow it to meet its goals.
The Corvette is unique in that it's a front- mid-engine design with a very low hood line, and when we looked at compact double-overhead-cam architectures, they just did not fit. One of the reasons the "small-block" V-8 engine has been around so long is that it's compact, with a low height, and it makes a tremendous amount of power and torque.
So there really wasn't any reason to add extra technology for its own sake.
From an engineering perspective, I always find it interesting that the outside world considers pushrod engines to be "lower tech," when the opposite couldn't be more true. Look at the cylinder block of the LT1, for example—it's incredibly complex. There are oil galleries everywhere. We machine a cam bore [and] lifters. A DOHC block, by comparison, is extremely simple—there's not much to it.
There are only a few manufacturers in the world who [offer] engines with direct injection, variable valve timing, and cylinder deactivation: Lamborghini on the Aventador, Mercedes-Benz on the S-Class, and Audi on the 8-Series. Of course, those cars all cost $130,000 or more.
From an engineering perspective, if the goal is to come up with a small package with 460 horsepower, 455 foot-pounds of torque, and class-leading fuel efficiency, we have the highest-tech engine in the industry.
The advantages of direct injection are well documented. Are there any particular difficulties involved in designing a DI powerplant?
Oh, yes [laughs], a lot of difficulties. The novice might assume that you just move the fuel injector from the intake port to the combustion chamber and call it a day. But when the decision was made to go with direct injection on the Gen V, it became that the engine was going to need a complete "melt and re-core."
Pretty much every component is affected. The block is affected, because we have to come up with a way to mount and drive the fuel pump. The cylinder heads and pistons are different, because we have to be very scientific in the way we configure the combustion chamber.
If you do a really good job on a DI system, which requires millions of hours of computational time on the combustion system, you can have tremendous efficiency. We spent six million hours optimizing and refining the combustion chamber on the LT1.
As impressive as the LT1 is, many of our readers will be tempted to extract even more power using aftermarket speed parts. Is the ease of performance modification ever taken into account when you develop a Corvette engine?
It's not something we consciously consider, since we're designing and optimizing for our particular OEM-built [application], but it's something we're aware of. We pride ourselves on the fact that the small-block has always been an excellent crate engine, as well as a platform for aftermarket modifications. I don't think hot-rodders will be disappointed in the capabilities of the LT1 or in its ability to respond to [such] modifications. It will be a little more challenging, because of the DI system, but I never underestimate the intellect of the aftermarket in coming up with unique and novel solutions. [W]e expect they'll be able to wring out a lot more performance.
Given ever-tightening emissions and fuel-economy standards, is the era of large-displacement engines, à la the LS7, officially over?
I'd day that it's safe to never assume. People wrote off the small-block back in the '80s, but it continues to work, and be re-optimized year after year to make it applicable and current for the times we're living in.
In the old days, it was assumed that a large-displacement engine had to be big and heavy, with poor fuel economy. That's no longer the case. With the LT1, the 6.2-liter displacement was nothing more than an engineering variable, a tool that enabled us to meet our goals for horsepower, torque, package size, and efficiency.
Any closing thoughts?
I want to make sure we recognize the engineering team, who put in four-and-and-half to five years of work, pride, and honor in creating the next-generation small-block. They're a great team of experts, they're very passionate about the Corvette, and that passion comes shining through in what we've achieved with the LT1.