"It's a racer's dream!"
If you're familiar with the ultra-high-performance '12 ZL1 going on sale this spring, it shouldn't surprise you to hear those words from Tony Roma, ZL1's Program Engineering Manager. What should surprise you is that Tony wasn't talking about the ZL1--he was talking about the Chevy Volt.
Specifically, Roma was waxing poetic about the Volt's high-output water pump, which his team snatched from the GM parts bin to test on the supercharged, 6.2-liter LSA's intercooler circuit. The 556-horsepower LSA had gotten the nod for ZL1 duty--it was a dream engine for anyone who lived and breathed Camaro. But Roma's team had no intention of leaving good enough alone--after all, this mill was going into the baddest, most powerful Camaro ever. So Team ZL1 took one look at it, and then jolted up the Chevy Volt's pump with some extra voltage.
"The Volt's water pump is super efficient, super high-output," Roma explains. "We slapped that thing in there and hot-rodded it up: It runs at 50 watts in the Volt--we turned it up to 80 watts. And we found that starting with a really high-flow water pump on the intercooler's air side helped it end up being more efficient."
Efficiency and world-class, all-around performance were two attributes targeted by the ZL1 team from the very beginning as they set out to bring supercar technology and performance at a sports-car price. And they used nearby rival Ford and its GT500 as the benchmark.
"We felt that before the ZL1 came out, the GT500 was the class of the field in this market," Roma says. "We were definitely looking to redefine the segment."
However, the ZL1 team also had to keep an eye on the project's budget; besting the GT500 on the street and at the track was the goal, but they also had to keep the ZL1's price tag competitive. So the team stopped thinking like a car company, and started thinking like racers.
"Planning the ZL1 was not much different than what anybody who's building a high-performance car goes through," Tony reveals. "If you go buy a Camaro SS, have X number of dollars for performance upgrades, then start flipping through a performance catalog, you want to get the best components that you can afford, right? We did the same thing for the ZL1--we just did it on a really large scope and at a high level. So at the beginning, all of us racers sat down with pen and paper and said, 'If this part doesn't make the car go faster, it's not in.'"
While some items like the Corvette ZR1's 638hp LS9 engine were too pricey to be considered, the team was able to include most of the desired performance components (including the Cadillac CTS-V's powerful LSA V-8), and still hit the price point. Items not crucial to performance, like the interior, were put on the backburner.
"We saved money in lots of ways," Tony states. "We have only one forging for both the 5- and 10-spoke wheels. And we used just one new coupling for the rear halfshaft for both the inboard and outboard sides. That's just a couple examples of many in the ZL1 that people won't ever see. But when you look down the spec sheet, the important stuff is there, like an all-new diff and an integrated cooler to keep it cool. We took care of the big stuff, and then got conservative with things that people will never notice."
"The LSA wasn't much trouble to put in the Camaro," Roma says. The ZL1-spec LSA engine is only slightly different than the CTS-V's, with all internals exactly the same as the Cadillac-spec mill. None of its mods caused any significant problems for the Camaro engine bay--after all, the fifth-gen car was designed for the LS3/L99 V-8s of similar dimensions.
The team's biggest issues were the lid under the cowl, and the added length from the extra belt track for the supercharger.
"We had to use the CTS-V's alternator and water pump for the main belt track, as well as an idler where the power steering pump would be. We also had to move back the A/C compressor to the CTS-V and Corvette position, so the ZL1 has a unique one. This change made room for the V's supercharger belt track in front."
The ZL1's exhaust manifolds are of the LS3 design, but they're high-grade, cast stainless steel with stress relief cuts between the cylinders to deal with the LSA's higher temps. They link up with a 2.5-inch stainless exhaust system featuring a dual-mode muffler setup.
The wiring is different due to more sensors, and the CTS-V's/ZR1's E67 ECU is utilized, since the extra inputs are needed for the supercharger. Feeding that thirsty blower is a high-volume fuel pump, which sucks premium unleaded from a tank with an additional fuel pump pickup for those high-g corners.
To maximize airflow and power, the team added a secondary air inlet to the lower box on the air cleaner. A unique air filter with shallower pleats lowers the restriction. Computational Fluid Dynamics (CFD) was used to optimize the design, and the LSA's throttle body position allowed a lower-restriction duct.
While there were no changes to the 1.9-liter supercharger's four-lobe innards, gains were made thanks to the shape of the lid. The ZL1's LSA engine has a 9.1:1 compression ratio; its SAE-certified power and torque ratings were made at 9 psi boost.
Much of the ZL1's power increase over the CTS-V's 556 hp comes courtesy of efficiency gains found in the LSA's air-to-liquid intercooler.
"Compared to the CTS-V, the intercooler brick had to be pushed forward in the ZL1," Roma explains. "And because we ended up redoing the whole thing, we decided to optimize it."
The team analyzed the tube-and-fin cooler's water flow rate on both sides, the water flow rate through the tubes, and the airflow rate at the other side. The brick's dimensions and its fin pitch were optimized for pressure drop on the air side, as well as on the water circuit. And the pump and heat exchanger sizes were adjusted--the former thanks to Chevy's "hot rod" Volt.
"The ZL1's intercooler is incredibly efficient, and it keeps the intake air temps in the range where the engine keeps making great power," Roma says proudly.
Two stout transmissions back up the LSA's formidable power: a six-speed manual (MG9), and a six-speed automatic (MYD). Both will be available when the ZL1 ramps up production. The MG9 manual is a TR6060 with a stronger output shaft and an additional mainshaft roller bearing, which increases its torque capacity to 556 pound-feet, or 30 percent more than the Camaro SS's manual trans.
Gear ratios from First to Sixth are 2.66, 1.78, 1.30, 1.00, 0.80, and 0.63, and Reverse is 2.90. The ZL1 gets the same 240mm twin-disc clutch and dual-mass flywheel as the CTS-V. Faster, more performance-oriented shifts are thanks to a refined synchronizer design, and a GM-designed short-throw shifter. And yes, skip shift is still alive and well in the MG9. The MYD 6L90E six-speed automatic was a pleasant surprise on the ZL1 options list. Gear ratios from First to Sixth are 4.03, 2.36, 1.53, 1.15, 0.85, and 0.67, and Reverse is 3.06. The torque converter is a 112k, 300mm dual-plate converter clutch unit. (GM doesn't state stall speed for production converters, just k factor.) A plate-style trans fluid cooler is located in the radiator end tank, along with an auxiliary oil cooler.
The 6L90E offers drivers the choice of Drive, Sport, or Manual mode. In Drive, it features second-gear starts for a smooth daily drive; a temporary Manual mode can be enabled by using the tap shifters. Sport mode is more aggressive by starting in first gear, and holding each lower gear longer before the performance algorithm fires off a more aggressive shift. When Manual mode is selected, the 6L90E's gears are in your hands; automatic upshifts won't happen, even at fuel cutoff. And staged upshifts allow for lightning-quick shifting. WOT shift points are at 5800 rpm in Drive, and 6000 rpm in Sport. "The 6L90's calibration is completely unique, and calibrated with a true performance enthusiast in mind--especially in Sport mode," Tony says. "In fact, we added line pressure to certain maneuvers just to get the correct 'quality' that we think our customers are looking for. This is also the first time GM has ever used every single performance algorithm (and invented some new ones) on one car at the same time."
When asked about driveline changes to handle all of that torque, Tony responded with, "Every single thing that transmits power in this car was revised: input and output shaft, couplings on the prop shaft, larger bars, everything. Wait…I think the lug nuts are the same."
Roma and his team put a ton of effort into designing the ZL1's 9.9-inch diff so it would not only appeal to both quarter-mile fans and road racers, it would also withstand the rigors of both environments.
"We didn't ignore the drag racers at the expense of the road racers, or vice-versa," Roma says. "The diff had to be for both groups. Take the 250mm ring gear: you don't need it that big for a 7:41 Nürburgring run. But if you put the small road race ring-and-pinion in, you're going to be disappointed at the dragstrip. The compromise is difficult, but I think we've done a good job with it." Originally, the ZL1 team wanted to use aluminum, but they couldn't build an aluminum housing to their satisfaction, so they stayed with cast iron. Rear gear ratios are 3.73 for manual-equipped cars, and 3.23 for auto-equipped cars. And the diff's stacked-plate cooler can drop fluid temps by up to 100 degrees! One look at the ZL1's asymmetrical axles, and you'll realize how serious the team was about combatting wheelhop. As Roma puts it, the team went "mondo" with the passenger-side shaft. This hollow piece measures 60.5 mm, and also has a stiffness ratio of more than 2:1 compared to the solid 33.25mm driver-side shaft. This construction helps disperse stored-up energy, which would otherwise cause performance- and driveline-killing wheelhop.
Compared to the SS, the ZL1's kinematics are the same. However, better handling is achieved by how the ZL1's rear stabilizer bar mounts to the lower control arm. Roma explains: "We moved the interface of the stabilizer drop links from inboard of the spring on the LCA, to outboard of the spring on the LCA. It gives it a more favorable motion ratio for the wheel, and it makes a bar with the same diameter four to five times more effective than the 2010-11 SS bar." (GM recognized how effective that suspension change would be in mitigating understeer in the Camaro SS, so it was added as a '12 SS Coupe option as part of the FE4 package.)
The ZL1 uses solid 25mm front and 28mm rear stabilizer bars, along with a variable rate 70 N/mm to 45 N/mm spring in the rear; the front 27 N/mm spring rate is the same as an SS. Massive, 220-treadwear Goodyear F1 Supercar G:2 tires measure 285/35/ZR20 front, 305/35/ZR20 rear. Because of the larger rear tires, and the cradle-to-body and control arms-to-cradle mounts, many of the ZL1's suspension bushings were stiffened up. The large rear tires generate so much more force, that they will cause too much deflection, and start to make toe change in unwanted places. The front strut and rear shock body bushings are also stiffer, thanks to the unique and powerful Magnetic Ride Control dampers.
Magnetic Ride Control
The ZL1 is the first application of the Gen 3 Magnetic Ride Control (MRC) system. It is completely new, truly revolutionary--and with 1,000 adjustments per second, it reacts incredibly fast. The last-generation magnetic dampers worked by using one wire with a natural ground loop that fed in current, and then naturally let the magnetic flux decay. While innovative, it reacted much slower than the new Gen 3 MRC does. Along with new ride height sensors, the new damper technology uses two wires and two smaller magnets, so the current can be reversed to break down the magnetic flux field faster. Everything the Gen 3 system does is faster: the MRC controller's processing rate, the input and filtering processing, how it thinks and changes parameters--even its hardware. While all of that is great on paper, we asked Roma to give a real-world scenario of the Gen 3 MRC's capabilities.
"Let's say I'm on a [road race] track, on corner entry," he starts. "I'm dialing in to the apex, trying to get the car to rotate in. The Gen 3 MRC can immediately stiffen up the rear shocks on corner entry so I can start to get the car to rotate. Now that the car is rotating, I've slowed down the body motion at mid-corner. What I want now is more control to the front, while letting the rear break so the front washes out a bit.
"We have a powerful algorithm that moves the roll stiffness to make it seem like the rear is stiffer on corner entry. On corner exit, it takes the stiffness out of the rear, so you can put torque down and drive out of the corner. A traditional active setup can't react that quickly. Even if it could, it would feel like you were driving a brick because it doesn't have as much bandwidth to change damping. But with Gen 3, the shocks can react fast enough and with enough authority to do it on the fly! That's what it can do for you that no system--passive or active--in the world can compete with."
Performance Traction Management
The ZL1 is blessed with a slightly modified version of the Corvette ZR1's sophisticated Performance Traction Management (PTM) system. The PTM system consists of the aforementioned Magnetic Ride Control, Traction Control, Stability Control, electric steering, and Launch Control for six-speed manuals. PTM has five modes that the driver can select, with each one offering a different combination of Performance Traction (Wet, Dry, Sport 1, Sport 2, and Race), Active Handling (three On, two Off), Suspension Mode (two Tour, two Sport, and one Track), and Steering (two Tour, two Sport, and one Track).
"ZL1's PTM system is very closely related to the ZR1, but we made changes to the Bosch software specifically for [the] Camaro," Roma says. "Most of the code was straight from the ZR1, but even though the core algorithm is the same, we did incorporate software and calibration changes for [the] ZL1. "PTM is a great example of how GM's hot rodders are working together to produce world-beating products. The ZL1 team started with the Corvette ZR1's production PTM program, but because the Corvette team had learned some things too late in development to be used on the production ZR1--"Engineers are never done," Roma laughs--they gave the ZL1 team lots of input.
"The ZR1 guys came in with their lists and said 'Hey, these are the things we would have liked to do.' We tried them, and we liked some of them. Because we had the time, we were able to incorporate the improvements into the ZL1's program."
The Launch Control system functions through the Electronic Brake Control Module (EBCM) and the Engine Control Module (ECM), and is fed signals from the wheel bearing-based ABS sensors. The EBCM is where the wheel speed inputs go; it has the algorithm that requests whatever torque it thinks it needs. Most of the system's brains live in the EBCM, but the ECM holds the RPM and cuts spark/fuel/throttle. In short, the ECM does the torque mitigation and figures out how to deliver the torque, and the EBCM figures out how much torque it wants and makes the request. "A good driver can beat the Launch Control by usually 1 to 2 tenths," Tony admits. "But the Launch Control is consistent all day long. It factors in a cold outside temperature and knows that the engine is making a little more torque, or knows the engine is a little warm and is making less torque, and adjusts accordingly. This system's consistency prevents an inexperienced driver from going up in smoke because of a track or weather change."
Electric Power Steering
Compared to the existing Camaro's fixed assist power steering, the ZL1 needed a sophisticated electronic system because the car's performance went beyond what a standard fixed assist system could handle.
"The ZL1 pushed Camaro beyond what would be acceptable for one assist setting," Roma starts. "When you tune a fixed system (one setting for power steering assist) on a car, you have to come up with one setting that's not too heavy for parking lot speeds, and not too light for high-speed driving. Because the ZL1 has wider tires and more front axle mass, it would have heavier effort in parking lot maneuvers needing more assist. And because it goes 30 mph faster than an SS, it would require less assist to not be 'darty' at highway speeds and above. We needed a variable assist solution to handle this. "EPS has the added benefit of being able to discern between driver inputs (from the steering wheel) and road inputs (from the tie rods), and it can mask out unwanted inputs from the road. We can also vary the assist and 'damping' that the driver feels versus the speed, and we can change it for different driver modes."
Besides a few minor changes, the ZL1's 14.6-inch, 6-piston front/14.4-inch, 4-piston rear Brembo brake system is the same as the CTS-V's. The major change lies in the front brake rotors. The CTS-V has "co-cast" rotors, where the cast iron portion is machined, and put into a mold with aluminum, then finish machined. The end result is a solid rotor with good directional stability.
In contrast, the ZL1 uses two-piece rotors--a hub, and a rotor with no centersection. To hold the rotor and hub together, they are attached by springs, bolts, and nuts. When the ZL1's brake assembly gets hot, this setup lets the rotor move. It is designed and meant more for serious track usage, as racers will get these brakes hot and cool them down often. The only downside is that owners won't be able to turn them; when the rotors are worn out, they'll have to be replaced. As the ZL1 has turned in some ridiculously short braking distances, we doubt they'll mind.
The ZL1's new hood is aluminum, with a carbon fiber insert. Forged wheels drop rotating mass, and the team even spec'd out a lightweight tire package from Goodyear. "We worked wherever we could to get the lightest possible solutions to our performance problems--though in some places it wasn't possible due to the loads generated," Tony says. "We wanted a lightweight solution for the hood and centersection. These parts are critical because they are above the center of gravity and very far forward, so a premium was put on them for that reason. All in all, the ZL1 is only about 220 pounds heavier than a 2SS."
The '12 ZL1 is one of the first GM cars designed to create downforce, or negative lift. To accomplish this impressive feat, the ZL1 team spent around 100 hours testing at the General Motors Aero Lab (GMAL) wind tunnel, using Computational Fluid Dynamics. The team leaned on GM's Lead Development Aerodynamics Engineer, Tom Froling, as this retired F-16 pilot and aero expert played a big role in helping to form the ZL1's body. However, the initial goal for ZL1 wasn't a full-on aero package; it was to eliminate the Camaro's tendency to lift at high speed.
"The SS was styled to be beautiful, but the car's shape came at the expense of lots of front lift," Roma reveals. "But, that's not much of a problem for a car limited to 155 mph. As you go faster than 150, forces and lift go up exponentially. We knew that with the ZL1's additional power, it would spend more time at high speed. So we decided early on to add a front splitter, as we wanted a more aggressive front anyway." The splitter not only took care of the lift problem, it also added an aggressive look to the front end. A unique rear spoiler was added, and then the team was faced with the most difficult component of the aero project: the hood extractor. True to its name, the extractor provided cooling airflow, and also assisted in reducing front lift. But just when Tony and his team designed the perfect extractor for aero-world, the real world called. "Once we designed a great extractor, we looked at it and thought, "Wait…this thing has to sit out in the rain! And we knew that if the driver wasn't careful, this extractor was going to get everything in the engine bay wet." It took some effort, but eventually a water trough was created to work with the extractor.
"It was then that we thought, 'If we keep going, we can make some downforce,'" Roma says. So several sizes and shapes of rocker moldings were tried before they found the right one. Front wheelwell extensions were put in as functional styling elements, as they gently move air around the tires at speed, and also assist with brake cooling. The team played with varying sizes and numbers of slats for the upper and lower grille. And a rear diffuser that utilized wraparound elements was chosen.
Roma is quick to note how beneficial Froling's airflow expertise was to the ZL1 project.
"Tom made a huge impact on [the] ZL1. As an example, he really pushed the idea of a belly pan. We weren't sure, as you have to be very careful to not choke off airflow paths from the engine, and if it's done wrong they can inadvertently bake things like starters. "But we made one, and it turned out to be a win-win. The pan funnels air over the driveline, and directs air up to the rear trans mount, which made it run cooler. We ended up in a better place because of guys like Tom." The end result is a ZL1 that produces 65 pounds of downforce at an equivalent 150 mph--compared to 200 pounds of lift in a Camaro SS. And that downforce translates into lower lap times, too. And while top-speed stability is great, these aero pieces also enhance handling and braking when the driver is actually obeying posted speed limits. "The closer you get to zero lift, the less the body moves--even at 70 or 80 mph on the highway, the ZL1 feels more stable," Tony says. "It is less sensitive to forces like crosswinds, too. In the end, it's all about being a driver's car, and giving you that confidence."
The Camaro ZL1 is available with six options: the six-speed automatic transmission with TapShift controls ($1,185), a 20-inch bright aluminum wheel package ($470), a power sunroof ($900), a stripe package ($470), an exposed-weave carbon fiber hood insert ($600), and a suede package, including suede microfiber accents on the steering wheel, shift knob, and shift boot ($500).
Despite the fact that the ZL1 tips the scales at over 4,000 pounds, the combination of its 580 horses and 556 foot-pounds of torque, its highly advanced suspension, braking, and traction management systems, and its sticky rubber makes for stunning all-around performance. While the sub-4-second 60 times and 12-flat quarters, and the 1g of lateral acceleration is impressive, we heard some eye-opening off-the-record testing numbers. Our favorite involves Tony Roma and Aaron Link, a ride and handling development engineer, booming out a top-speed Autobahn whopper. While GM's Communications team requested that I stick with the "official" performance numbers, take it from me that they are…conservative…
The Future of the ZL1
"There are a lot of things that GM is doing to make sure we meet today's legislation and social requirements, but there is still a desire for performance, especially on the Camaro lineup," Roma says. "Al [Oppenheiser, ZL1's Chief Engineer] is a Camaro and performance guy at heart. And GM's current leadership definitely recognize that it's required for the Camaro to have an ultra performance version for credibility. And myself and all of the other Camaro fans out there are pretty happy to hear that!" While there has been no announcement of 2012 production numbers, and no future ZL1 model years announced, here's hoping that this fantastic Camaro sticks around for a long, long time.
Horsepower: 580 at 6000 RPM (SAE CERITFIED)
Torque: 556 at 2400 RPM(SAE CERITFIED)
0-60 Time: 4.0 Seconds (Manual)/3.9 Seconds (Automatic)
Quarter-Mile ET/MPH: 12.1 Seconds (Manual)/12.0 Seconds (Automatic) at 119
Top Speed: 180 MPH (Manual)/184 MPH (Automatic)
Nurburgring Time: 7:41:23
Lateral Acceleration: 1.0G
Curb Weight: 4,120 Pounds
Weight Balance, F/R: 51.7 Front/48.3 Rear
Fuel Economy: 14 City/19 Highway (Manual) -- 12 City/18 Highway (Automatic)