Charles Beyer's '04 GTP Comp G comes out of the chute at Cordova Dragway during the '05 GP
Under the hood of the Comp G we see the sanitary installation and the stock location of ma
A Precision T-61 turbo is located in the area normally taken up by the stock airbox. Insta
Where's the blower pulley and snout? Actually, the only thing left from the original Eaton
We recently had a chance to drive an '04 Pontiac Grand Prix GTP Comp G that ranks as one of the quickest street cars any of us had ever driven-period. How quick is that, you ask? You're probably thinking, "Sure, they're quick, but have you guys been piloting Azteks for so long that it's warped your sense of what performance is?"
Rest assured, this thing rips-with a best of 12.125 at 116.78, through the mufflers, no less. A chassis dyno session revealed it made 401 hp at the wheels. Do we have your interest now? The secret is a slick turbo kit from Cartuning (www.cartuning.ca) that mates a well-matched turbocharger to the 3800 V-6 to pump out some explosive acceleration, without the bad kind of explosions to spoil your good time.
"Wait a minute, don't the Comp Gs come from the factory with a supercharger?" you ask. "What's wrong with those?" Well, nothing really. The Eaton M90s are great for street use and give a tremendous amount of low-end power. The problem in using them is that they generate a lot of heat, are difficult to intercool, and ultimately, cannot flow as much air as even a moderately sized turbo.
Also, don't forget that a supercharger is crank driven while the turbo is exhaust driven. The more boost you try to make with a supercharger, the more power it takes from the engine to turn the supercharger. An Eaton Model 90 will require something along the lines of 35 hp to make 10 psi. Obviously, you have a net gain there, but if you consider a turbo doesn't take any energy from the crankshaft, the turbo will make more power from this fact alone (not even discussing efficiencies). While it is possible to get an Eaton M90-equipped GTP into the 11s or even the 10s, it will be compromised as far as street performance goes.
Charles Beyer, of Digital Horsepower (www.digitalhorsepowerinc.com), is someone who really appreciates a sleeper. You may remember his centrifugally supercharged '97 Grand Prix SE from one of our HPP Pavement Pounder Shootouts a couple of years ago. While it was a low-profile performer, it was not quite what he wanted. "I would still have that car today if this turbo kit was available back then," Beyer says. "The CSC worked great, but it was pretty loud. With a turbo, it's only noisy when it's making boost. The CSC wasn't god-awful loud, but enough that any potential victims would realize something was definitely not normal. The turbo isn't too 'noisy' (i.e. bad noise), it just doesn't audibly make itself known until it's too late."
This time around, Beyer decided to work over an '04 GTP Comp G, getting the additional benefits of an upgraded suspension and brakes. What's amazing about the finished product is that not only is it insanely quick for a front-drive street car (or any street car, for that matter), but it also displays flawless street manners.
Best of all, it is 100 percent bone stock except for the turbo kit itself, which includes some larger injectors and a PCM reprogrammed by DHP. There is absolutely nothing exotic or even aftermarket in the long-block. It uses untouched production heads, a stock cam, and a factory-issue bottom end-even the exhaust manifolds are production units. It's as-built Detroit iron assembled by union labor at GM Powertrain. 'Nuff said there.
A Cartuning kit retains stock exhaust manifolds and mates them to the turbo by way of a cu
A Cartuning air-to-air intercooler mounts behind the front bumper cover just ahead of the
A Turbonetics wastegate mounts between the engine and firewall and is adjustable. Beyer us
So what about this kit? Cartuning, a Canadian firm, spent about 18 months developing a turbo kit for 3800-powered W-bodies that is flexible enough to give the buyer some options, yet is by no means a trouble-prone "cafeteria plan." Various turbo upgrades and an intercooler kit are available for those who want to build a full competition setup.
The kit has already produced some impressive results. Development was conducted on a stock L36-powered Grand Prix. With a baseline of 160 wheel horsepower (195-200 SAE net depending on year), Cartuning claimed its Performance Stage 1 Turbo Kit made 280 hp and over 300 lb-ft of torque to the wheels. That equates to about 350 hp at the crank. The company adds that the Stage 1 kit is completely streetable and suitable for customers who want to bolt-on a turbo kit to a stock L36 vehicle. The Stage 1's turbo is good for up to 425 crank horsepower with additional supportive mods.
Putting The Kit To The Test
In Beyer's case, his kit as installed in the Comp G uses a larger Precision PT 60-1 turbo (a T04-B P trim Garrett is standard), which will support 700 hp, if he dares. He also opted for the Cartuning air-to-air intercooler. The basic kit also uses a stainless steel ducting from the turbo compressor to the throttle body, a Turbonetics EVO wastegate, a Monza blow-off valve (BOV), and a custom-made stainless steel exhaust crossover assembly that mates perfectly to the stock exhaust manifolds. Also included are new flow-matched Lucas/Delphi 65-lb/hr fuel injectors, a custom reprogrammed PCM, hardware, gaskets, hoses, instructions, and so on.
This kit was designed around the stock cast-iron exhaust manifolds, which were retained for their durability, resistance to leaks, and the exhaust velocity they generate. To those who believe headers are the only way to go, rest assured, you'll be able to make more than enough power to grenade the transaxle without them.
The exhaust side is finished off with a custom stainless steel crossover assembly, specific mandrel bent, TIG-welded, 2.5-inch stainless steel downpipe with a U-bend removal and a CarSound high-flow catalytic converter. Happily, the outlet bolts directly to the stock exhaust system or Borla, DynoMax , or SLP systems to greatly simplify installation.
Since Beyer's car was a supercharged GTP, he was left with the task of choosing an intake manifold, which he handled cleverly and inexpensively. "I've seen guys spend over a grand on a custom sheetmetal intake manifold, but I'm not one to throw around money like that," he says. "I just took the impellers out of the stock M90 and used Cartuning's optional L67 adapter kit, which blocks off the open end with an aluminum plate. That way the throttle body and injectors are left in their stock locations. It works great."
The Monza blow-off valve vents excess pressure away from the compressor when the throttle
The Cartuning 3800 turbo kit comes as a completely engineered kit, down to the high-capaci
Talk about a sleeper! Though the Grand Prix GTPs have a good reputation for performance, t
Beyer says the performance increase was huge, knocking more than 2 seconds off the Comp G's e.t. and adding over 15 mph to the trap speed. Our seat time in the Grand Prix confirmed that, even with the boost down from 17 to 12 psi, this car was an absolute rocket, yet it idled and otherwise behaved like a stocker. From a 15-mph roll, the V-6 was able to easily overpower the tires, and while torque steer was present, it wasn't enough to cause any concern. The GP zipped up to 100 mph at least as quickly as a Z06 Corvette, almost too quietly to realize just how fast this car really was. When the throttle was let off, the BOV let out a loud hiss and the 3800 quietly coasted back to legal speed.
As quick as the GTP is, we were astounded to find out later that it was running with a damaged turbo. An air filter was accidentally left off during a visit to a quickie oil-change emporium and some debris was able to enter, damaging the compressor. Beyer noticed the torn blades while at the racetrack and decided to run anyway, as the compressor turned freely, though it wasn't grabbing air like it was intended to. Still, he managed to make quite a showing.
"My first pass when I drove in was a 13.2 at 110 mph," Beyer says. "I paid my money at the gate and got in line with all the stuff in the trunk and with street tires. Once it started hitting 12s, things got fun as people kept coming to the pits to see what just beat them. I took out a few Mustangs, which was easy, and an E55 AMG Mercedes-just barely, though. Even with the slicks, it couldn't hold traction.
"I didn't see the damage to the compressor wheel until I was at the track prepping it. But I basically said, 'Screw it, we're already here, so let's see what happens.' We got stuck at 12.1. I tried giving it more boost, but it didn't run faster. Evidently, the damaged turbo was at its limit. All the later runs were between 12.1 and 12.4 and around 114-117 mph."
The results, while not perfect, were still spectacular. With a fully functional turbo, this car would have been well into the 11s-it was nearly there to begin with. The Cartuning kit, as Beyer installed it, cost just under $4,500. Granted, that's a pretty stout chunk of change, but if you add up the cost of the ported heads, the cam, the headers, the oversized throttle body, and the nitrous system, you're most likely money ahead. Best of all, the turbo kit can be moved from car to car a lot easier than the aforementioned mods.
In this age of "trick of the week" hop-ups and frequently spending hundreds, if not thousands, of dollars for single-digit horsepower increases in late-model performance engines, the viability of turbocharging becomes more and more relevant. It remains one of the most effective power-producing modifications available and also one of the most cost-effective. Seventeen pounds of boost is definitely our idea of "displacement on demand."