Beginning in 1963, there were only two Corvette models: the coupe and convertible. The big-blocks came along in 1965 and by 1969 buyers had seven engine options over the base 327/300, including the ZL1. Fast-forward to 2010 and buyers had six models to choose from, with the stout 430hp LS3 for the coupe, convertible, and Grand Sport coupe and convertible; the 505hp LS7 for the Z06; and the 638hp LS9 for the ZR1. That’s a tough act to follow, but so far, the C7 is showing us it’s got plenty of mojo.
The new LT1 is different enough from the LS3 to be considered GM’s Gen V SBC. While some enthusiasts get frustrated because GM almost never does anything “revolutionary” with their engines, their “evolutionary” method is working well.
Minutes after the C7 made its debut, fans asked, “Where’s the Z06?” Well, Z06s are on the road now and they’re “OMG!!!” machines. Packing an LT4 engine with 650 hp and 650 lb-ft of torque, enhanced suspension, tires, brakes, and full-out, race-track-proven ground effects, the new Z06 slams everything that came before. Where the C6 Z06 was a beast at the limit, the C7 Z06 is predictable and controlled. Where the C6 Z06 was somewhat floaty at top speed, the C7 Z06 is glued to the pavement, but won’t have a higher top speed because of the wind drag from the ground effects.
How did Corvette engineers pull this off based on the new LT1? The sum of the parts equals the whole. Little improvements here and there, plus a smaller, more efficient supercharger did the trick. Suffice to say that the LT4 is like a classic SBC from the past—lots of red meat left to exploit. Here are the highlights. It’s not just the numbers. Yes, the LT4 delivers more horsepower and torque than the LS9, but not that much more. However, the LT4’s peak torque comes in 1,500 rpm earlier than the LS9’s, giving the Z06 a stronger, wider powerband. This, coupled with improved suspension, tires, and brakes, makes the C7 Z06 a complete system.
The block and crankshaft are the same as the LT1’s, except for a few minor enhancements for durability, and the oil system has been improved slightly. The LT1 and LT4 heads were developed together with their combustion chambers designed digitally before being cast in aluminum. The heads flow better than the LS9’s and are designed so that the burn starts in the center of the chamber. Compression for the LT4 is 10.0:1, compared to the LT1’s 11.5:1. The valve angles are the same for both engines, however, there’s slightly more exhaust lift for the LT4, and the LT4 has unique valves, seats, and composition. The lubrication system functions at two rates: 44-58 psi at normal operation and 65-72 psi under load. Plus, the oil pan has a cooler with 20 percent more cross section. The higher-flowing fuel pump delivers 2,900 psi into each fuel rail versus 2,175 in the LT1 (a 26 percent increase).
Because of safety considerations, the supercharger-intercooler unit had to be 3 inches shorter. Engineers accomplished this by using smaller diameter and longer rotors, allowing the intercoolers to be placed between the rotors and rocker covers. The intercooler has 50 percent more cooling fins and a volumetric efficiency of 92 percent, versus 89 percent efficiency for the LS9. While the LT4’s rotors have less displacement, the small diameter allowed them to spin at 20,150 rpm, versus the LS9’s 15,080 rpm, and the smaller rotors needed less torque to drive them. Overall, the LT4’s supercharger system is 20 pounds lighter.
And that’s the Cliff Notes version of the C7 Z06’s LT4 engine. Early versions were pulling 680 lb-ft of torque. A little exhaust, camshaft, and chip work and 700-plus is reasonable. This is just the beginning; wait till the aftermarket gets a hold of the LT4. Will there be a ZR1 version or will we have to wait for the mid-engine C8? We’ll see!