As Pontiac sails off into the sunset, we recently had the chance to indulge ourselves with their last truly great car, the G8 GXP. We decided that even though it is a very respectable car straight from factory, some sections of the car could use some work. Two of those areas in need of attention are the intake and exhaust. We wanted to remove the rat maze of an intake system and replace it with something more direct and to the point. The same could be said for the exhaust. The OE mufflers provide a great sound that will entertain you for little more than the drive home from the dealership before you’ll be begging for more sound and power.
There is a reason most enthusiasts start their aftermarket lives with doing an intake or exhaust upgrade. These basic modifications provide the necessary foundation for other go fast parts such as heads or a performance cam. But to really get this car’s tires screaming, we also added a custom tune from SCT Performance.
Here is a brief overview of what we installed:
- Granatelli Motorsports G8 Cold Air Intake System (PN 500015-P, $279.99 retail)
- Corsa Performance Dual Rear Exit Exhaust with Pro Series Tips (PN 14950, $1,309.95 retail)
- Custom Tune from SCT using the X3 Power Flash Programmer (PN 3400, $479.00 retail)
Let’s take a closer look at the parts we installed, starting at the intake.
Granatelli Motorsports G8 Cold Air Intake System
One look at the design differences between the stock and the GMS Intake make it crystal clear as to why this intake can increase power. Where the stock system is littered with different chambers and bends to keep intake noise to a bare minimum, the GMS version utilizes a large tube with gradual bends to maximize air flow. But it has more than that. One key item found in every intake is the filter. “To help keep costs down, the OEMs equip new cars with your standard paper air filters. While these systems do a fine job of trapping dust and debris and keeping it out of the engine, they are horribly restrictive and limit power,” said JR Granatelli, owner of Granatelli Motorsports.
Granatelli includes a cone style high flow filter with their system. Unlike the factory paper filter, this dust trap can be washed and reused instead of just being replaced when dirty. That helps you keep your engine breathing clean without the burden of purchasing paper filters all the time, so you’re not just getting more air – you’re also reducing the amount of trash that ends up in the landfill over the life of the car.
From the filter, the air travels through the stock MAF sensor and through the large 4-inch diameter tubing on its way to the throttle body. GMS offers three different finishes for this intake: satin, black, or polished like ours. All the clamps and hardware needed to complete the install are included as well.
Installation of the GMS Cold Air Intake
Anyone that can change a light bulb can install this intake. It all starts with getting the stock rat maze intake out of the car. This is easily done by loosening the clamps that hold the system together, along with with popping the clamps on the filter box and removing the bolts that hold it in. This took about 5 minutes to complete, and we were ready for the GMS Intake.
First up was the section of tubing that would connect the throttle body to the MAF sensor. This was installed by slipping the rubber coupler over the throttle body and connecting the first finished bend tube in place. From there, we added another rubber coupler and attached the MAF. The rubber couplers were held in place using the supplied clamps that Granatelli Motorsports includes with the kit.
We attached the remaining components to the inlet side of the MAF sensor, and finished it off with the cone filter at the end of the system.
Corsa Performance Dual Rear Exit Exhaust with Pro Series Tips
More air in means more air out. To give the exhaust gas direction, we picked up Corsa Performance’s Dual Rear Exit Exhaust with Pro Series Tips. Corsa spends an insane amount of time in the design phase of their products, and the products that come out of their building show their attention to detail.
One thing Corsa prides themselves in is creating an exhaust note that’s custom designed to provide a pleasurable sound. While everyone has their own opinion on what a good exhaust sounds like, Corsa’s thoughts are clear. “We pride ourselves in producing an exhaust that fits good and has no drone,” said Craig Kohrs of Corsa. “Noise is not sound to us. We have the technology to be able to fine tune the exhaust sound to exactly what we want it to be,” he explained.
Fit and sound aside, the Corsa exhaust has other benefits as well. The mandrel-bent system helps the exhaust gas flow 68% better according to Corsa. They also claim a significant weight savings. “We were able to really lighten this system up and ended up removing 11 lbs on each side,” Kohrs said. “That means this kit is 12% lighter overall compared to the stock system.”
The fit and sound are what can really make an exhaust, though. The flow claims seem plausible, and just looking at the bends and design of the muffler on the Corsa system compared to the stock counterpart makes this point clear. “If you wanted to, you could drop a golf ball in at the top of this system and it would roll right out the other end, even through the muffler.” explained Kohrs. “That is how open this exhaust is.”
Removing the stock exhaust system was simple. GM did a nice job designing this car to be easy to work on in this situation. The stock exhaust sits pretty much below everything, including the independent rear suspension. That meant all we had to do was unbolt a few clamps and we were able to start pulling tubing out of the car.
Up near the front of the car, we unbolted the stock H-Pipe and got ready to install the new Corsa kit. We chose not to remove any other components of the car including heat shields or brackets for two reasons. First, many of the brackets were going to be reused with the Corsa kit. Second, we wanted to test the fitment of the kit with as much of the original equipment as possible.
The stock exhaust unbolts just after the catalytic converters, and that is where the Corsa system picks things up. The system starts out with a pipe that connects the plumbing after the converters to the the rest of the system. In doing so it also moves the exhaust to the center of the car, following the path of the stock exhaust through the midline of the vehicle.
Once making the turn back toward the outside of the car, Corsa places a flex joint here. This is to help compensate for the expansion and contraction that stainless steel can experience in different temperature ranges. This also helps keep the amount of squeaking and rattling down.
Before long, our GXP was ready to be lowered off the Bend Pak lift. The last thing we did was hang the mufflers and tighten everything down.
To really take advantage of all the free flowing air, we decided to add a custom tune from SCT. First, we wanted to get a base line of the horsepower before the tune, so we moved the GXP over to the DynoJet 424x dyno and made a total of two runs. The numbers were impressive. The LS3 turned out a solid 365 horsepower and 367 ft/lb torque. Not bad for a factory tune with a few bolt-ons.
SCT said they could do better. The weapon of choice for SCT’s own Chris Johnson was the X3 Flash Tuner. This power tuner would allow us to make the necessary changes to the G8’s computer to really bring out its inner muscle car. “We went with a performance tune that is very similar to what we would do to the Corvette or Camaro with the same engine,” said Johnson.
The wide open throttle fuel and timing maps were adjusted to ensure the right amount of fuel and spark was being delivered to the engine at the right times. Johnson also added, “Because this car already had an aftermarket intake and exhaust, we used our tune that corresponded with those upgrades. That way we were able to get the most power out of those modifications.”
One thing that many owners have brought up with these newer cars is the lack of “feel” behind the pedal. This is due to the advent of Drive By Wire technology that has replaced the traditional cable that once linked the pedal to the throttle body. “With the X3 we are able to tune the Drive By Wire system and give it a more responsive feel that you would normally associate with the older cable systems,” explained Johnson. In addition to that, the SCT tune adjusted the computer’s Torque Limiters to let the engine work more comfortably without being held back. It also removed both the rev-limiter and speed limiter. At this point our G8 was ready for anything!
The X3 is such a powerful tuning tool, that it also lets you perform custom tuning on your car. You can adjust fuel percentage, timing, and even shift points on automatic cars. So even if you think the tune that comes with the device is powerful, picture what you could do after fine tweaking it for the best results.
After a few quick minutes, the tuning process was complete and we were ready to pull the car back onto the DynoJet dyno to see what kind of results we got. The results were impressive. We saw 380 HP and 381 TQ, an increase of 15 WHP and 14 WTQ! Keep in mind that this is on top of the gains we’d already seen from the intake and exhaust.
With no more than a day’s worth of work, our silver GXP that once blended in with the crowd transformed into a growling, easy breathing pack leader with close to 400 rear wheel horsepower. The best part is that all these mods are easily accomplished by anyone who knows which way to turn a wrench using only common tools. The fit and finish of both the Granatelli intake and Corsa exhaust are up to the high standard we expect for our G8, and the SCT tune not only got us more power, but also improved how the Pontiac drives at part throttle as well.