Personally, I thought the whole move to a hypercar was a bad move, as what made the Corvette an interesting sports car was it’s comparable affordability. Though when pickups and Jeeps can be over $100,000, I suppose the Stingray at $70,000 base isn’t too bad. And when considering hypercar prices, even the full performance hybrid at just over $200,000 isn’t terrible. And it would probably survive track days better than a Viper. Anyway, an interesting article on how they increased the RPMs and made the engine lighter and more powerful. Kind of similar to what they’re doing with a lot of motorcycle engines.
https://www.jalopnik.com/2029555/chevy-flat-plane-crank-corvette/
By Charles Krome
Already a star, the Chevrolet Corvette went supernova when the mid-engined version debuted in 2020 — but that was some six years ago, and the location of the car’s engine isn’t as big of a deal as it used to be. Nowadays, there’s more buzz for the type of engine it uses: A 5.5-liter V8 with a flat-plane crankshaft is standard in the Corvette Z06, ZR1, and hybrid ZR1X, the latter able to run the quarter-mile in under 9 seconds as the fastest, most powerful production Corvette ever. In fact, with that twin-turbo V8 and hybrid assistance combining for 1,250 horsepower, the ZR1X can outrun plenty of aftermarket builds, too. It’s the kind of extreme performance that requires a sophisticated engine, and that’s where the flat-plane crank business comes into play.
The distinctive design of the engine unlocks supercar levels of excitement in part because it allows the motor to rev so high. In the naturally aspirated Z06, capable of delivering 670 hp, the redline is way up at 8,600 rpm; the ZR1 makes its peak four-figure horsepower number at 7,000 rpm. Flat-plane engines are also generally lighter and more compact than typical cross-plane V8s and better at exhaust-gas scavenging. And flat-plane crank V8 engines sound so distinctive it’s hard to mistake them for anything else.
Of course, all that’s just for starters. Let’s get into the nuts and bolts of engines with flat-plane crankshafts to see how they do what they do.
The differences between flat-plane and cross-plane crankshafts
When a piston engine is running, those pistons move up and down in their cylinders. The crankshaft, in turn, is the first step in transforming that vertical movement into the rotational motion needed to get your wheels moving. Without getting too deep in the details, the bottoms of the pistons are connected to the crankshaft, which is like a specially designed metal rod that runs in the same orientation as the engine itself. But it’s not just a purely straight length like a broom handle. Some of the straight sections are replaced by crank pins where the pistons attach.
Imagine a very simple two-piston setup: when one piston is at the lowest point in the cylinder, the hump of its crank pin points straight down so the connecting point is below the centerline of the crankshaft, and when the other is at its highest point, the hump of its crank pin is pointing up. As the pistons move up and down, they push and pull the crank pins to turn the shaft.
Expand that to a four-cylinder engine and we can see the difference between cross-plane and flat-plane crankshafts. The former will have each of the four crank pins set off by 90 degrees compared to the next. So looking straight at the end of a crankshaft, they make a cross pattern. A flat-plane engine has the crank pins at 180 degrees, creating, well, a flat plane.
The bottom line
Let’s put it all together by putting a pair of I4 engines together to make a V8. With a cross-plane V8, the crankshaft requires counterweights to help even out the vibrations caused by the motion of the pistons. That means the crank itself is heavier so that more of the engine’s power is wasted turning that shaft instead of the wheels. The light weight of a flat-plane engine lets it spin faster to make more power — a heavier, cross-plane crank, also including a heavier crankcase, is one reason your daily driver can’t rev like a supercar.
Flat-plane engines do have second-order vibrations, and that’s a key reason they aren’t as common on the street. But in racing, a little extra shaking is worth it for the added power you get — and the same holds true for the road-legal Corvettes. Plus, Chevy did make some concessions to reducing second-order vibrations, such as shortening the piston stroke (but while increasing the bore to maintain displacement).
A further factor is the firing order of the pistons. In a cross-plane V8, the firing intervals within each cylinder bank are uneven, while a flat-plane setup has the firing order alternate from bank to bank. This improves exhaust gas scavenging, which uses the flow of exhaust gas to help get more exhaust out of the cylinder while increasing how much fuel/fresh air comes in. With all that, it’s no wonder so many people consider the C8 the best ‘Vette yet.