Over the last 20 years, electronic control has become the norm for pretty much every part of mass-produced vehicles. Starting with electronic fuel injection, then spreading to computer-controlled transmissions, today it’s hard to find any significant system in a new car or truck that isn’t ruled by the flow of ones and zeros. While the performance aftermarket has embraced this in some ways, like the blossoming of the ‘professional tuner’ industry, in many other ways we’re still bolting dumb old parts to our increasingly smart hot rods.
You won’t find a domestic performance car that more fully embraces the advantages of the digital revolution than the C7 Corvette Stingray, but closely consider it and you’ll see that it really represents a blend of the best of the analog past and the high tech future. The LT1 under the hood is a pushrod, two-valve, big displacement V8, just like the ones GM has been making for the last 60 years, right down to the bore spacing. And it’s complete with variable valve timing, direct injection, drive-by-wire, and cylinder deactivation, all orchestrated by a sophisticated engine management system.
The Corvette’s 8-speed automatic transmission uses a torque converter, planetary gearsets, and wet friction clutches just like a Powerglide, but its own controller packs more processing power than it took to send men to the moon and return them safely to earth, and it shifts itself faster than Porsche’s fancy dual-clutch gearbox. Even the instrument panel combines high-resolution digital displays with analog “steam gauge” dials.
What makes the ProCharger i-1 unique is the variable ratio drive system. In place of the single-speed step up gearing used in a conventional supercharger drive, the i-1 has a computer controlled continuously-variable transmission (CVT) that connects the crank-driven belt to the compressor unit. This allows a wide range of boost variation, regardless of engine speed.
A Perfect Match
It’s only appropriate then, that in our quest to upgrade our project Stingray, dubbed C700, to 700 crank horsepower, we’d pick a power adder that also embodies the both the analog and digital worlds. ProCharger has an extensive line of Corvette systems, and they’ve recently added their revolutionary i-1 technology to their Corvette options. We were fortunate enough to be among the first to receive a C7 i-1 system – in fact – this is the second production kit that ProCharger built, and since we’d previously installed and tested one on a 5th Gen Camaro, we were eager to find out how the variable-drive-ratio supercharger would translate to the new LT1 engine platform.
Driven Racing Oil LS30
Since our intention is to keep asking our stock LT1 engine to produce more and more power, we need to do everything we can to keep it healthy and happy internally. As part of our supercharger installation, we took the time to upgrade to Driven Racing Oil LS30 synthetic 5W-30.
This oil is specifically engineered for the unique requirements of both naturally aspirated and forced induction LS and Gen V LT engines, with high temperature and high shear resistance thanks to its advanced synthetic base stocks.
LS30 utilizes the right cold viscosity for optimum flow on start-up to fight hydraulic lifter ‘ticking’ and deliver consistent VVT operation, and the low-volatility formulation reduces PCV system blow-by. It also features a high-zinc content, helpful for longevity with aggressive cam profiles.
You might think that with direct injection and all the other new technology that it came with that change would be the biggest obstacle. As it turns out, the task of adapting the i-1 to the new generation engine turned out to be more analog than digital. “The biggest hurdle for that application was fitment,” ProCharger’s Cliff Hall admits. “What we ended up with was a package that was shoehorned in, but it worked out pretty well. We’ve got a fairly small belt with good belt wrap, and it’s a dedicated drive system, so all in all it’s a pretty nice kit.”
Compared to the LS3’s 10.7:1 compression ratio, and the LS7’s 11:1, the LT1 runs 11.5:1 compression – typically not good news when you want to add some boost. However, Hall says, “The direct injection gave us the buffer and allowed us to still run seven pounds of boost and still have accurate and stable fuel and injection conditions.”
“These LT1’s are surprisingly strong,” Hall asserts. “The thing is that everybody wants to run pump gas so it’s usually the tune that hurts the engine. If you have the right tune-up the engine will withstand a lot of horsepower.
Of course, the challenges and opportunities inherent in the new LT1 engines will apply if you’re talking about a conventional fixed ratio supercharger as well. What sets the i-1 apart from the competition, and even ProCharger’s own fixed-ratio systems for the C7, is the fact that it can electronically control boost thanks to the integrated continuously-variable transmission that takes power from the belt drive and delivers it to the centrifugal compressor.
One important feature of all of ProCharger’s supercharger systems is the documentation that comes with. In our experience, there’s nobody out there that beats their manuals for completeness and clarity.
In The Mode
The i-1 offers several different modes of operation, selectable by the driver on the fly. “It’s similar in concept to a lot of higher-end cars that change shift points, engine settings, and traction control,” Hall explains. “Touring mode sets the ratio as fixed, which keeps it quieter and gives you better fuel efficiency. It typically makes 1.5 to 2 pounds of boost at peak engine RPM on a stock application. Sport mode is where you see the benefit of the CVT being added on to our high-speed gearbox. It ramps in the boost at a lower RPM and you get a flat boost curve – typically by around 2500 RPM you are at peak boost and it maintains that through to redline. Competition mode is intended more for track use. It basically ramps up the boost quicker – you’ll see it more or less instantaneously at wide open throttle.”
By dynamically controlling the speed of the supercharger, independent of engine speed, the i-1 can deliver a radically different driving experience than the typical centrifugal blower. Hall says, “You’re going to get that seat of the pants feel like you do with a positive displacement supercharger, and you’re going to maintain that higher boost level through the entire RPM range because it’s electronically controlled and you’re at a higher efficiency level.”
With the system in our hands, we set out to begin installation. One thing that ProCharger really has nailed down over the years, we’ve found, is the “installer experience.” All their systems come with detailed, step-by-step installation and instruction manuals that are illustrated with color photos and computer-generated drawings for every significant stage. The C7 i-1 system is no exception; read the manual before you begin and there will be no surprises.
To begin, we had to say goodbye to our tried-and-true K&N intake system. To provide access for the new intake tubing, intercooler, and the supercharger itself, the bumper cover, fender liners and splash guards, and the radiator fan all get temporarily removed.
ProCharger supplies very well-engineered bracketry to mount the i-1 supercharger and CVT drive.
There isn't a ton of room under the C7's hood, so ProCharger's major challenge with the i-1 was achieving good belt wrap and a physical package that would fit properly.
ProCharger offers air-to-air intercoolers in both horizontal and vertical mount versions. Hall’s recommendation for a daily driver? ‘I would say the vertical, with the exception of somewhere with extreme temperatures; if you live in the desert, for example, and it’s going to be 110 degrees all the time. Otherwise the vertical is going to be your best performance option.’
With the i-1 installed, all the stock bodywork back in place, and the touch-screen controller mounted inside the car, the physical part of the job was finally complete.
Protecting Your Investment
Anything you have to cut, we supply. – Cliff Hall, ProCharger
Another area that ProCharger really gets right with this system is the fact that should the day ever come when we want to return our Stingray to factory condition, we haven’t made any irreversible alterations to the car. “Anything you have to cut, we supply,” Hall explains. “There is some plastic shrouding for the front that we actually send with the kit so that it’s 100% reversible. We did that on the C6 systems as well. For example, in order for the intercooler tubing to fit to go back up to the throttle body, the inner fender liner needed to be trimmed. To be consistent, since we supplied that piece for the C6, with the new Corvettes we supply the front shroud piece.”
Ryne Cunningham of CMS was enlisted to provide a tune to account for our previously-installed long-tube headers and free-flowing exhaust.
Once our i-1 was installed, there was one additional thing to take care of – the tune. The typical stock or near-stock C7 owner will be able to take ProCharger’s complete system and use the tune that’s part of the package, but because of the level of modification we’d already accomplished on C700, we turned to our go-to GM tuning guy, Ryne Cunningham. Owner of Cunningham Motorsports, he’s seen a lot of C7s come through his shop since the car was first released, and he quickly got our tune dialed in to take full advantage of the new manifold pressure.
Testing on our Dynojet revealed an additional 102.8 horsepower and 126.3 pound-feet above our previous naturally-aspirated peak, for a total of 541.5 and 579.2, respectively. Pay particular attention to the table-top flatness of the torque curve between 2,300 and 5,000 RPM – This is where you really feel it in the seat of your pants.
The Burden Of Proof
Prior to the supercharger installation, we’d seen a peak of 438.7 horsepower and 452.9 pound-feet of torque to the wheels on our Dynojet chassis dynamometer. We’d achieved those numbers – an increase of 41.3 horsepower and 74.9 pound-feet over the initial stock dyno pulls – with a combination of a free-flowing K&N intake system, Billy Boat long tube headers and exhaust, and a professional tune from CMS. With the i-1 installed and set to competition mode, producing seven pounds of boost, C700 spun the rollers to the tune of 541.5 horsepower and 579.2 pound-feet of torque for a gain of 102.8 horsepower and 126.3 pound-feet compared to our previous naturally-aspirated peak numbers. Notably, the engine is delivering more than 500 pound-feet right across the board, starting way down at 2,300 RPM and not beginning to taper off until the point where the horsepower curve catches up at 5252.
On a stock C7 (without the headers and other bolt-ons) and running the higher quality fuel found in other states, based on other ProCharger installations, the gain would typically be well above 150 horsepower to the tires at 7 PSI. Stock or modified, the i-1’s power delivery curve and instant boost transforms the C7 driving experience.
To ensure our additional power wasn't converted directly into tire smoke, we stepped up to a pair of Mickey Thompson ET Street S/S DOT-approved drag radials in 305/35R18 size. They're available in 15-20 inch sizes and use M/T's R2 compound - the same rubber found in their full competition drag radials.
So close to the tens…
We were eager to actually put the new-found power to use, so we made our way to the Auto Club Dragway at Fontana, California to see how it translated into lower elapsed time. Bone-stock and on the factory tires, we managed a best pass of 12.23 seconds at 116.24 miles per hour, with a 1.99 60-foot time. Now, with an additional 144 horsepower on tap compared to that first test, and shod with sticky Mickey Thompson drag radials, C700 pulled a 1.68 60-foot and blazed through the quarter-mile in 11.08 seconds at 126.19 miles per hour; tantalizingly close to breaking into the tens.
One thing of note – our i-1 was in Sport Mode not Competition Mode. Sport mode offers a moderately aggressive boost curve, while “Competition” offers maximum boost for slick, drag radial, and other sticky-tire vehicles. Unfortunately, the race track has a series of oil-downs, and we weren’t able to secure further testing in the Competition Mode. We will soon and we will provide an update. But make no mistake – this is a serious 10-second car. We just ran out of time to prove it. But we will.
To meet our goal of 700 crank horsepower (call it 595-plus to the tires, once you factor in driveline loss), we need to crank up the boost a bit more beyond the seven pounds we’re making now, but that’s still in the future. Keep an eye out for the full details on adding water/methanol injection, upping the boost, and getting another demon tweak from Cunningham Motorsports.
Thanks to the combination of the i-1’s broad, flat power curve, the sticky Mickeys, and the factory 8-speed automatic, C700 is a very rewarding car to drive on the dragstrip.
In the meantime, though, we’ll be enjoying C700’s enhanced power, delivered in a way you can only experience via the technological wizardry of the i-1. ProCharger’s Tyler Van Lant puts it best; “This is a great match for a C7 if you want that instant torque. With it, you have the advantage of that down-low torque that makes it fun to drive, and the efficiency of the centrifugal supercharger, and more horsepower than you get with a positive displacement blower anyway.”
UPDATE: Adding Extra OctaneWhile we were duly impressed with the performance that the i-1 afforded us, we couldn’t help wanting to give our new setup a bit more of an edge. Being based here in California, we’re mostly limited to 91-octane gasoline at the pump (unlike in Eastern areas of the country that commonly offer 93- or 94-octane gas). Wanting to see how our now-Procharged ‘Vette would handle the advantage of East-coast gas, we decided to re-tune the car for 94-octane fuel.As an alternative to driving hundreds or thousands of miles to get our hands on 94-octane, we carefully mixed 91-octane pump gas and VP Racing‘s 101-octane race fuel to simulate it. After filling up, Cunningham Motorsports took over for the re-tune and then it was back to the dyno.
On 94-octane gas with an accommodating tune, Project C700 put down 571.2 horsepower and 599.4 pound-feet at the rear wheels.
From a change in fuel alone, we saw a gain of 29.7 horses and 20.2 pound-feet of torque. Eager to get this newfound power on the strip, we cruised back up to the Autoclub Dragway in Fontana, California to lay down a few passes. On 91-octane, the Corvette completed the quarter-mile with a fastest time of 11.08 seconds at a brisk 126.2 miles per hour; with the new go-juice, however, C700 crossed the line with a 10.89 seconds with a best of 128+ mph – shaving off 0.19 seconds and picking up almost 2 miles an hour.
Thanks to the extra octane, now our Stingray’s dipping into the tens like we wanted and is inching closer and closer to our 700 crank-horsepower goal.
The righthand column shows C700’s times – notice how we also knocked 0.14 seconds off our eighth-mile time.