Low-flying ’Vettes: NA C7 vs twin-turbo C6

There is no denying the performance credentials of any car deemed fit — by the GM suits — to bear the legendary Corvette badge. Since the 1950s, the Corvette has been the sports car that every manufacturer has kept a wary eye on — while outright performance may have suffered for a period, thanks to factors such as the ’70s oil crisis, the Corvette has always delivered everything the badge demands. 

In recent years — really, beginning with the fifth-generation C5 — the Corvette has stepped up as a true competitor to European performance vehicles, for a fraction of the price. Detractors would point out the ‘quality’ differences between the Corvette and its European contemporaries, and, while they’re potentially not wrong, the Corvette’s bang-for-buck factor cannot be overstated. These issues with the quality — generally pertaining to the interior plastics — have been steadily addressed by GM, with the sixth-generation C6 being a significant improvement over the C5 in this department, while the brand-new C7 is light-years ahead of just about any high-performance offering to come out of the US — ever. 

With the new C7s having only recently begun to find their way to New Zealand shores, this presented us with a question to which we didn’t even know we needed an answer: if you’re in the market for a Corvette C7, what would be better — a new C7, or a C6 with the change spent on serious performance upgrades? Now seems to be a fitting moment to introduce our competitors. 

New and improved: the C7

In the yellow corner, we have a 2014 Corvette C7 — an almost total redesign of the preceding sixth-generation C6. Obvious aesthetic changes aside — enhanced on this example by the Z06 front and rear spoilers — one of the biggest structural changes for the C7 is the hydro-formed aluminium chassis across the range. The lightweight and rigid frame is enhanced through the use of carbon fibre in the bonnet and a removable roof panel, as well as fibreglass composite fenders, doors, and rear quarters. Making the most of the thorough structural revamp is a revamped mill beneath the lightweight bonnet — GM’s latest Gen V small block, named the ‘LT1’, which is good for 450hp from the factory. This one’s been fitted with an aggressive aftermarket cam and a Borla cat-back exhaust, bringing the power figure well north of the 500hp mark. 

The all-new LT1 is backed by a new Tremec TR6070 seven-speed manual transaxle, complete with rev-matching ability, and comes equipped with the optional Z51 performance package — this means performance brakes, performance suspension, dry-sump lubrication, 19-inch front and 20-inch rear wheels, and electronic LSD. While the magnetic ride control (MRC) magnetorheological shock absorbers developed by GM and Delphi are an option with the Z51 package, this example retains the Z51-standard FE3 system, comprising front and rear double-wishbone suspension with sports-tuned coil springs, composite transverse leaf springs front and rear, and nonadjustable shocks. It may sound like an agricultural system, but it’s simple and works extremely well.

Just as the exterior has been totally reworked, so too has the interior. It’s just as nice inside as it is outside, with good design that is streets ahead of previous-generation Corvettes in terms of both design ergonomics and quality. Yes, in comparison with European alternatives, it does feel a little American, but, if you’re in the market for a high-performance GT, you’ll struggle to get more car for your money anywhere else. There aren’t many C7s in the country yet, and an example like this would set you back somewhere just north of NZ$110K, making it a potential alternative to that top-of-the-line HSV. 

Of course, compared with even the flashiest of HSVs, the Corvette feels special. You sit extremely low in the cockpit, and, from the driver’s seat, everything feels at hand — it is definitely a driver-oriented vehicle. A HUD (heads-up display) provides instant information on the car’s behaviour, and the seven-speed manual shifter is well weighted and positioned, although four H-pattern shift gates do have the potential for you to momentarily lose track of which gear you’re in when you aren’t driving it as if you had stolen it. Then there’s the features that just make it a nice place to be — the upholstery stitching is consistently tidy, innovative features like the storage cubby behind the retractable infotainment screen are welcome in a car not renowned for its interior storage capacity, and Bose sounds reinforce the fact that this is a car you can drive daily.

All this is one thing, but, chances are that if you’re reading this in the first place, it’s what happens when you flatten the loud pedal that you’re really interested in. Compared with earlier generation Corvettes, the C7 has been thoroughly refined, and this has been extended to the driving dynamics. Floor it, and, when a C6 would be a hairy companion, the C7 just does the job with minimal drama, squatting and launching towards the horizon at an extreme pace. No doubt the chassis’ extra rigidity plays a part in the planted roadholding, as the suspension geometry is very similar to that of the C6, and the LT1 produces more than enough power to get you to ridiculous speeds with ease, with the Borla exhaust making all the right background noises. With all that power on tap, as well as the comfortable cabin doing a fair job of isolating you from the outside world, the HUD comes in pretty handy for ensuring you know just how fast you’re going. 

Rebuilt to perform: the C6

In the other yellow corner, we have this 2007 Corvette C6 Z06 — although there’s little original Z06 remaining underneath that bonnet. The Z06s were incredibly engineered cars from factory, with a dry-sumped alloy LS7 producing 505hp in conjunction with such weight-saving measures as a magnesium-alloy engine cradle, alloy frame, and composite flooring panels. However, despite the incredible performance, there’s always going to be someone who needs just a little more — that’s why, if it’s ever possible for a factory high-performance sports car to earn the ‘sleeper’ tag, we’d give it to this car in a heartbeat.

Why? Well, this particular Corvette is a lot more than it seems, with a spec list that reads more like an entire speed shop’s worth of extreme high-performance parts. The original LS7 is long gone, and in its place is a super-tough seven-litre V8 based on a trick Warhawk LS7X block filled with top-of-the-line parts, including a Callies rotating assembly and ARP fasteners. The heads are ported Warhawk items, and the valvetrain is a seriously awesome assembly, too. However, the combination’s crown jewels aren’t even visible within the confines of the engine bay — the Air Power Systems (APS) turbo kit, based around twin Garrett GT3582R ball-bearing turbos and a pair of TiAL 44mm external wastegates, is tidily tucked beneath the Corvette. Such an extreme engine package means it’s good for 1002hp at 15.5psi of boost. Having been built to handle in excess of 30psi, the car’s owner, Mike, has plans to fill the engine with the boost it was built for, and this should see the already massive power figure skyrocket further — along with its on-road performance. 

The factory Tremec T56 six-speed manual transaxle is still there, but the addition of a SPEC twin-plate clutch has seen it hold up well to the four-digit power and torque figures. A Driveshaft Shop heavy-duty driveshaft was a must, for obvious reasons, and rounds off the bulletproof engine and driveline. With the level of power on tap, Mike is still able to turn the rear tyres into smoke at just about any speed in any gear — despite the rear wheels being enormous 18×13-inch units, wrapped in chunky BF Goodrich 335/30R18 drag radials. Thirteen inches is as much width as the guards will accommodate, and the 18s are the smallest-diameter wheels that will clear the rear brake calipers — although Mike has said he’d like to go down a size to 17 inches to get more tyre sidewall and improve traction, telling us, “It’s still able to smoke the tyres at 200kph in fourth!” When he can get traction, the results are nothing short of incredible, as Mike says: “I have run, up an incline in fourth gear, from 100 to 250kph in 7.1 seconds.”

Aside from the monstrous power figure it channels, the driveline’s real talking point concerns the gearing. With such a large power output and its ability to smoke the rears, this Corvette has been geared for outright speed — more than 400kph, in fact. Mike has taken it up to 360kph — with a lot left in it — and did have plans to take the New Zealand land-speed record currently held by the FreemanX Lamborghini Gallardo, at a two-pass average of 355kph. 
“I’ve had it up to 360kph at 4700rpm in sixth — I had to shift up, unfortunately, as it’ll only do 330kph in fifth!” Mike says, adding, “That was running on 13psi of boost. High boost is 15.5psi, and the engine has been built for 30psi.” 

Despite the enormous power and hearty driveline beneath the car, the Corvette is still extremely easy to drive. “You could daily drive it if you wanted,” Mike says. “I wouldn’t, but you could.” That drivability, as well as the higher boost levels planned, are made possible thanks to the Turbosmart e-Boost2 electronic boost controller. Though the controller allows for six preset boost levels, Mike’s currently only using four of them, and plans to add a 20psi and 30psi setting. Because drivability has always been key, the huge boost pressure won’t come on in one massive hit, either — the e-Boost2 allows for boost by gear; as the Corvette gains speed in each gear, traction is stabilized, meaning progressive power increases by gear can be more effectively put to the ground. At present, Mike’s got it set-up with 6psi in first gear, 9psi in second gear, 13psi in third gear, and 15.5psi in fourth and above, though he is considering the high-boost settings mentioned earlier, which would give 20psi in fifth and 30psi in sixth gear. 
Despite what you may think, given the relative lack of bolt-on aero, the car handles that sort of speed surprisingly well. On top of the chassis differences between the Z06 and the regular C6, the Z06 came with a lot of carbon-fibre panels as standard, saving additional weight. The tiny rear lip spoiler actually does a deceptively good job of keeping the car planted, as the airflow is supposed to follow the inwards taper of the roofline towards the spoiler. 

This particular Corvette is also on the market. Mike’s got it up on Trade Me — although he’s in no real rush to sell it, stating that he’d like to attempt a New Zealand land-speed record before the car sells. 

So, if you’re in the market for an outrageously quick car that will smoke the bags whenever you want, start first pop every time, and turn heads in the way that only a bright yellow Corvette can, get in there — the only thing cooler than having a 1000-plus horsepower weekend car would be having a certificate verifying it as the country’s fastest road car!

2014 Chev Corvette C7

• Engine: 6.2-litre GM LT4, alloy block, alloy heads, aftermarket camshaft, dry-sump lubrication
• Drivetrain: Tremec TR6070 seven-speed manual, electronic LSD
• Suspension: Double-wishbone, sports-tuned coil springs, composite transverse leaf springs, and nonadjustable shocks
• Brakes: Brembo, vented rotors
• Wheels/Tyres: Factory
• Exterior: Velocity Yellow, Z06 spoilers
• Interior: Stock
• Performance: Approximately 500hp

  2006 Chev Corvette C6 Z06
   

• Engine: 427ci GM LSX, Warhawk LS7X alloy block, six-bolt mains, billet-steel main caps, full ARP fastener kit, coated Clevite bearings, Callies crankshaft, Callies Compstar H-beam rods, Total Seal piston rings, Cam Motion camshaft, Morel lifters, Comp Cams pushrods, Comp Cams 919 dual valve springs, custom Crower shaft-mount steel roller rockers, Katech C5R timing chain, ported Warhawk LS7X 12-degree six-bolt heads, 296cc intake runners, 110cc exhaust runners, 2.250-inch intake valves, 1.625-inch exhaust valves, port-matched APS custom turbo manifolds, two Garrett GT3582R water-cooled ball-bearing turbos, two TiAL 44mm external wastegates, custom mandrel-bent APS twin three-inch exhausts, Turbosmart e-Boost2 electronic boost controller, two-bar manifold absolute pressure sensor, front-mount plate and bar intercooler, twin in-tank fuel pumps, Teflon-lined stainless fuel lines, APS fuel rails, APS 95-pound injectors, ATI harmonic balancer, billet rocker covers, billet coil-pack relocator, ported Corvette Z06 oil pump, priority main oiling, Ron Davis Racing Z06 radiator, Royal Purple lubricants
• Drivetrain: Tremec T56 six-speed manual, SPEC ST-Trim twin-plate clutch, Hurst billet shifter, Driveshaft Shop 3.5-inch heavy-duty 6061-T6 aluminium driveshaft
• Suspension: Corvette Z51 handling package uprated springs, uprated shocks, uprated sway bars
• Brakes: Six-piston front calipers, four-piston rear calipers, cross-drilled rotors
• Wheels/Tyres: 18×10- and 18×13-inch Forgeline SP39 three-piece wheels, BF Goodrich 295/35R18, BF Goodrich 335/30R18 drag radial tyres
• Exterior: Carbon-fibre front splitter, Z06 carbon-fibre fenders and roof, carbon-fibre boot spoiler
• Interior: Stock
• Performance: 674 hp at 6psi boost, 785hp at 9psi boost, 930hp at 13psi boost, 1002hp and 1032lb·ft at 15.5psi boost; engine built for 30psi 

This article was originally published in NZV8 Issue No. 128. You can pick up a print copy or a digital copy of the magazine below: