Anyone want to guess what the codename "BAS" stands for?
Thanks to its monstrous 6.2-liter supercharged LT5 V8 engine lurking under the hood developing an insane 755 hp, the new 2019 Chevrolet Corvette ZR1 is the most powerful Corvette ever produced, marking a return to the fabled ZR1 moniker for the first time since the C6 ZR1 finished production in 2013. Automotive News recently spoke with engineers at Chevrolet to gain a further insight into the engine’s development, revealing that it shares the same architecture as the LT4 V8 used in the Z06.
While the LT5 uses the same block, head, pistons, and connecting rods as the LT4, it does have some unique components: namely its massive supercharger, which is the largest GM has ever produced. Also new for the ZR1 is a dual fuel system, two engine controllers to control the fuel system, modifications to the lube system, a different crankshaft material made of a higher-strength alloy, and a shaker hood. But it’s the new imposing supercharger poking through the hood that’s arguably the most important element of the new ZR1. According to Juechter, Chevrolet wanted to keep the powerful engine a secret during development.
So they had to come up with a generic internal codename that wouldn’t attract attention. Dodge did the same thing when developing the Demon. Internally it was known as ‘Benny,’ since ‘Demon’ or ‘Hellcat’ aren’t exactly subtle names. The Corvette ZR1’s engine, on the other hand, was given the codename ‘BAS’ instead of ZR1. The intention was to fool employees into thinking it was referring to the Belt Alternation System that a GM diesel engine uses. But the engineers used BAS to stand for ‘Big Ass Supercharger’: a fitting name, considering that the ZR1’s LT5 V8 is 52 percent bigger than the LT4 used in the Z06, hence the need for a shaker hood.
“It’s the most efficient and the biggest supercharger the Corvette has ever had,” said Jordan Lee, chief engineer of the new LT5. It displaces 2.65 liters of air for every rotation and has a 170-degree helix rotor set, making it more efficient than the 160 degrees in the LT4. “That 170 degrees compared to 160 degrees for the LT4 is mostly done to improve the efficiency of the rotors,” Lee explained. “As they’re compressing air, you want to make sure you don’t get any leakage past those rotors. 170 degrees ensures a tighter seal.” Surprisingly, the supercharger spins slower than the one on the LT4 at 15,860 rpm compared to 21,000 rpm.
“We wanted to slow the supercharger speed down to introduce a lot less heat,” said Lee. “So running slower is more efficient.” However, the LT5’s supercharger generates 110-hp just to keep it spinning. This required an 11-rib drive belt to accommodate the extra energy required to spin it. In contrast, the LT4 only needs eight ribs on its drive belt. “So effectively, this engine’s making 865-hp,” said Lee.