That’s about 20 hp more than the estimates from General Motors’

powertrain gurus when they unveiled the new ZR1 and its monster motor last December.

To simplify the math: The LS9 engine in the ZR1 is rated at 103 hp per liter of displacement, or 1.7 hp per cubic inch (6.2 liters is equal to 376 cubic inches, for the old schoolers in the audience.)

All that power will push the Corvette ZR1, which goes on sale this summer, to a top speed of more than 200 mph, GM says.

What about the grunt? The official number is 604 lb-ft of torque.

The key to that making all the horsepower and torque is a Roots-type supercharger with four-lobe rotors that sits atop the LS9 engine. A liquid-to-air intercooler is integrated into the supercharger’s housing.

The engine will be hand-built at GM’s Performance Build Center in suburban Detroit, the same plant that hand-builds the LS7 V8 used in the Corvette Z06.