By the sixth-generation Corvette, the GM engineers weren’t leaving much on the table with the factory EFI calibration. There were some gains to be had in terms of street manners, but not much to speak of on the top end. That all changed, though, when Chevrolet went to unleash the 2015 Corvette Z06 on the world. It was well known that the 650-horsepower animal was given a conservative tune to meet strict emissions standards and hold up for the duration of the 100,000-mile warranty. You can hardly blame them for either, but at the same time – we want more power (amiright)!
Those in the know are aware that this is a simple problem for the likes of Howard Tanner at Redline Motorsports. The Pompano Beach, Florida-based shop tunes everything from the 2,000hp twin-turbo C6 Z06 shop car to stock C5s. When a customer’s 2015 Corvette Z06 was dropped off for a few standard bolt-on upgrades, we decided to take a little detour by tickling the keyboard after the baseline dyno pulls. Tanner uses several different tuning programs, however, on this particular outing he choose HP Tuners’ laptop-based software to interface with the Z06’s computer, just like on his 10-second ’14 Stingray. See what it takes to add over 30 rwhp and plenty of torque under the curve on a 2015 Corvette Z06 without even touching a screwdriver.
Redline Motorsports began by strapping this bone-stock 2015 Corvette Z06 down to its in-house DYNOmite chassis dyno. This particular dyno is load-bearing, which best simulates the load that the engine will see from driving on the road. In theory, this would allow the tune to be more precise and negate much of (if not all) street tuning.
The HP Tuners interface plugs into the OBD-II port under the dash and connects to a laptop.
Howard Tanner looks over the stock tune file in the software after pulling 581 hp. He noted that the ’15 Corvette Z06 was difficult to get a consistent baseline. When we asked if it was heat-soak from the supercharger, Tanner said the Intake Air Temperature (IAT) didn’t seem indicate that it was the cause.
Tanner used the HP Tuners data logging feature to keep an eye on vitals such as the air/fuel, spark advance, Mass Air Flow, and Knock Retard. Spark and fuel changes were not unlike any C6 or C7, except that the factory tune left the tailpipes dripping with a 9.5-10.0:1 air/fuel ratio.
One of the biggest differences, Tanner says, with C7 tuning is the more advanced variable valve timing. “The camshafts are installed ‘advanced’ and the cam phaser is commanded by the ECM to retard the timing as dictated in the WOT tables for cam timing. However, as cam timing is changed, so is spark timing as the VE (volumetric efficiency) is also changing. The trick comes from making a cam timing change and not getting a huge timing swing as the ECM believes the VE has changed.”
Power would come from adding spark through the entire curve (except over 5,500 rpm), disabling the Cat Over Temp (COT) Protection, and adjusting the fueling to hit 11.5-12.2:1. If you plan on road racing your C7 Z06, then leaving the COT enabled is recommended to preserve the catalytic converters during long periods of wide-open throttle. For stoplight racers, it is just a hindrance by making the Z06 pig-rich. There are a few other tables Tanner goes over, such Knock Recovery, that help ensure you are getting all 650 hp when you want it (though not necessarily affecting the peak hp).
With the custom tune, peak horsepower reached 612, but it was even more impressive how much further the torque curve carried. The Z06 picked up power throughout the rpm range and boasts a new peak of 598.8 lb-ft of torque. Now it is time to play with some bolt-ons!