When Chevrolet officially announced the new Corvette ZR1 just before the Detroit Auto Show this year, it hadn't yet finished the certification of its new power-plant, the supercharged LS9. At that time, all the engineers would tell us was that the supercharged 6.2L V8 would produce a minimum of 100hp/L or 620 hp. Three months have passed since we got our first official look at the LS9 and the numbers are now in. According to GM, the LS9 has now been SAE Certified at 638 hp and 604 lb-ft of twist. The official EPA fuel economy testing hasn't been finished and for people who buy a ZR1 it probably won't matter anyway. Nonetheless, GM expects the LS9 to be the most fuel efficient 600+hp engine in the world, a dubious distinction if ever there was one. A special team of technicians will be hand-building and testing the LS9 at GM's Performance Build Center in Wixom, Mich. Check out the articles below for all the details on the ZR1 and LS9.