Without question, it's fun to buy, build, or drive a street sleeper--a car that is much faster than it looks. General Motors hit the nail on the head when it unveiled the Pontiac G8 GT, as it has all sorts of awesome features to make for a very fast car, while the sedan body style certainly throws people off course. Regardless of the car's sleeper status from the factory, we wanted to pep it up a bit, without giving away too much of the car's quiet and non-descript attitude.
As many of you know, the L76 is a cross between a couple of great LS engines. Starting with an aluminum 6.0-liter block (like the LS2), the L76 comes with Displacement on Demand (aka Active Fuel Management), which is the ability to deactivate four cylinders for better gas mileage, and a capable set of L92 heads with an LS3-style intake manifold. While it doesn't match the potency of an LS2 or LS3, it easily outperforms the Vortec truck engines in cranking out 361 horsepower from the factory. All that power is great, but when you combine it with a 4,100-pound, four-door sedan, it could use a bit more steam to keep up with the Corvettes.
Before we get to modifying our '09 test car, we would first have to establish a baseline. The G8 GT doesn't require premium gas, so all of our testing was done on 87-octane gasoline to provide the most real-world results possible. First we visited the local eighth-mile dragstrip for a few baseline passes. The car performed well, but definitely needed some tweaks to get the full potential out of the L76 engine. Running a best of 9.257 at 76.53 mph, the obvious area for improvement is in the first half of the track, as its 60-foot time was a staggeringly slow 2.200 seconds.
Most of this is due to the drive-by-wire system resisting the urge to go wide open throttle even though the pedal was to the floor. Surprisingly, the car never tried to spin the tires off the line during the baseline passes. Onto the baseline dyno pulls, the car showed its potential by cranking out 292 hp to the wheels on Injected Engineering's Dynojet dynamometer. In case you were counting, that's a drivetrain loss of approximately 19 percent from the factory horsepower ratings, which isn't terrible considering it has a power-robbing automatic transmission. Even with more than 50,000 miles on the odometer, the car made decent power on cheap gas, but there is obviously room for improvement.
For this, we decided to give it a couple of discrete modifications that would increase power, but keep the car under the radar. As much as we love the note of an LS engine breathing through an aftermarket exhaust system, keeping it quiet is the goal with this install. To help the G8 inhale a little easier, we trashed the original air box unit, in favor of a Vararam intake system, which offers fresh air from the car's grille, as well as a high-flow filter. The new cold air intake system takes all of the kinks from the original air box out of the equation, offering a straight shot to the throttle body. When we contacted Vararam, they were excited to tell us about a new product offering, which is essentially an upgrade from its previous cold air intake. This time around, the intake features a wider inlet, which is dyno-proven to increase power even more than the original kit.
With the Vararam piece in hand, we knew the G8 would also need a programmer to adjust the car's tune, in an effort to make more power. Our search led us to DiabloSport and its Trinity programmer unit. The DiabloSport programmer offered easy navigation of the tuning parameters, and all sorts of cool features to go along with the upgraded tunes. The install was extremely easy, as the DiabloSport kit came with all of the necessary hardware to get the job done. Aric Carrion of Injected Engineering then put the programmer to use on the dyno, and selected the Diablo Tune, as that was the only option for anything less than 91-octane.
Even with the cheap gas, the car gained more than 20 horsepower at the rear wheels, thanks to approximately 30 minutes of work, and absolutely no change in the car's everyday driving configuration. Aric said we could expect another 20hp or more by swapping to the more aggressive tune and fuel octane level. The final numbers for our testing are 313 hp and 335 lb-ft of torque, which is mighty impressive. More impressive was the fact that the car got 29.7 miles per gallon on the 100-plus-mile trip home. Granted, the trip was mostly interstate driving at 70 mph, but the car generally gets 27 mpg on the highway, so it was a noticeable difference.
At the track, the car made great gains in elapsed times, jumping from the initial 9.25 to a much quicker 8.854 at 81.08 mph. Better throttle response and quicker shifts helped the car tremendously, but the 60-foot times were still a bit slow for our liking, with a best of 2.11 seconds. Regardless of the sluggish start, the car pulled hard all the way through the RPM band and provided the kind of results we wanted to see. The best part about the entire install is the fact that no one can tell we've messed with the L76 engine, which further enhances the G8's sleeper status!