Everything works together to make 755 hp, but if you wanted to single out a single thing, you could point to that supercharger poking through the hood. When the engine was under development, they wanted to keep it a secret, so rather than stamp “Corvette ZR1” on the top, it said “BAS.” There’s a GM diesel engine that uses something called a Belt Alternator System, so that’s what they wanted people to think this was. But the engine engineers said that the “BAS” stood for something wherein the B was for “Big” and the S was for “Supercharger” and … you can guess what the A stood for.
“It’s the most efficient and the biggest supercharger the Corvette has ever had,” said Lee.
It’s 52 percent bigger than the unit atop the LT4 block, and it’s the reason for the shaker hood. It displaces 2.65 liters of air for every rotation. It has a 170-degree helix rotor set, the twist in the rotor set. It’s 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,” said Lee. “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.”
The supercharger actually spins slower than the one on the LT4: 15,860 rpm versus 21,000 rpm. The boost is 13.9 psi at peak.
“We wanted to slow the supercharger speed down to introduce a lot less heat,” said Lee. “So running slower is more efficient.”
Nonetheless, the LT5’s supercharger is drawing 110 hp to keep it spinning. That’s so much that it needs an 11-rib drive belt to accommodate the extra energy required to spin it. The LT4 only needs eight ribs on its drive belt. (Maybe ribs will become the cupholders of engine bays?)
“So effectively, this engine’s making 865 hp,” said Lee.
While many aftermarket parts makers will be tempted to offer a different-size pulley to increase the speed at which the supercharger spins, don’t be tempted.
“The aftermarket’s gonna be chompin’ at the bit to bring in a smaller pulley and overdrive this thing," said Juechter. “That invalidates the warranty. We designed this engine to be robust on the track, but it’s all optimized the way it’s designed now. Anybody throwing new parts at this, they’re taking their own risk. We stand behind it the way it’s built in Bowling Green.”
They have more confidence, too, thanks to no less than 13 radiators (or heat exchangers) used to keep it cool. The Z06 had some cooling problems, and the ZR1 should be totally cool. It’s more than radiators, though.
“From the A-pillar forward, a lot of the structure is new because we wanted to pack as much cooling content into the car as possible,” said Juechter. Cool air is routed to the brakes, too, as well as to rear-mounted radiators through openings on top of the forward surface of the rear fenders.
The result is an engine that is “not too shabby,” according to Lee. "The LT4 and LT5 feel similar off the line, but above 4,000 rpm it’s a whole diff world.”
We are looking forward to driving it sometime before the car debuts next year.