http://www.hotrod.com/feature_stories/1412_the_2015_corvette_z06s_lt4_v8/viewall.html
They are saying the Active Fuel Management lifters limited the camshaft in the LT4, and there is more power available there.
Sample:
The 0.551-inch lift on the LT1 intake and the LT4 exhaust is no coincidence; it’s the limit of the Active Fuel Management (AFM) lifters. The AFM system allows half of the engine to shut off by controlling oil to the four sets of lifters. With the lifters collapsed, the cam’s lift isn’t transferred to the valves and fuel is also shut off for those cylinders while the rest of the engine continues to run as a V4.
We asked Lee how much power was left in the factory fuel system. He told us that the limit is the DI pump, not the in-tank pump. Because the factory tune has to keep emissions components longevity in mind, they enrich the air/fuel ratio a bit, meaning there’s some “cushion” beyond the current 650hp rating, although there’s not a whole lot of room for a factory tune to eke out more power. However, he knows there are ways, adding “the aftermarket will do what the aftermarket will do.” By the way, the folks at Lingenfelter are already privy to the part number of the LT4’s Stanadyne direct-injection fuel pump.
When posed with the same question, Jordan Lee told us there’s still some power to be had: “I think there’s more in that supercharger.” John Rydzewski, who admitted that some early iterations of the LT4 were producing around 680 lb-ft of torque, was also free to admit where to find more power: “Open up the exhaust system and work with the camshaft.” If it weren’t for the stringent emissions requirements, “There’s a lot of room to move around on the camshaft.”
Again, Ford and Chevrolet work WITH the aftermarket......
