Thus far in our 2004 Pontiac GTO buildup, we had been adding a little performance here and there with some simple engine and chassis mods. These included: an air intake from LS1Speed; exhaust, sway bar bushings, and custom tuning from SLP Performance Parts; drag tires from Nitto Tire; and a skidplate, strut tower brace, and driveshaft loop from BMR Fabrication. (See the Jan. and Mar. '05 issues of GMHTP.) All of these items performed quite well and helped yield a well-handling, low-13-second street machine.
Pursuant to the old adage, "too much is never enough," we decided it was time to add some serious horsepower to our LS1-powered Goat-enough to blow the doors off of the Mustang Cobra, Chrysler 300C SRT-8, and 6.0L '05 GTO competition. Enter Vortech Engineering, one of the most trusted names in aftermarket supercharging systems.
Vortech's centrifugal supercharger kit for all 2004 (5.7-liter LS1) GTOs delivers 7-8psi of boost via it's quiet, proven V-2 compressor. This system is one of the cleanest as well; absolutely no accessory relocation is necessary, as the blower is driven off of a new pulley affixed to the power steering pump. Really, the only intrusions to the Pontiac's original underhood setup are slight adjustments of a few things like the power steering and coolant reservoirs. This is almost unheard of in the world of centrifugal supercharging.
In addition, Vortech uses air-to-water-to-air intercooling, or "aftercooling," to drop the temperature of the intake charge. This style of system does away with any added hassle of routing intake piping to a traditional front-mounted air-to-air intercooler. Instead, a mixture of water and antifreeze is pumped through a "charge cooler" box and then to the front of the car, where a heat exchanger cools the liquid via the rush of outside air coming through the grille.
Vortech claimed the kit would add 131 horses at the crank-a claim we would put to the ultimate test. To get baseline dyno numbers, we went to TT Performance Parts in Saddle Brook, New Jersey, specialists in LT1 and LS1 GMs. Strapped to TT's Dynojet 224x, our automatic-tranny GTO mustered 302.7 hp and 318.5 lb-ft. You may recall that this is significantly less than the 327 or so that we garnered previously in the buildup, and the reason is that we removed SLP's custom tuning prior to the latest test. This was to get a true appples-to-apples comparison of a stock-tune, naturally-aspirated GTO, versus a Vortech-tuned supercharged GTO so that the power increase seen with the blower wouldn't be confounded by extraneous variables. We're crossing our fingers to see upwards of 400 hp at the wheels post-installation.
Follow along in the photos as we begin the blower bolt-on on our Phantom Black test car. Next time, we'll finish the job by adding the blower ducting and aftercooler system. Then, we'll be about ready to get this show on the road and do some damage-to the competition and hopefully not to our drivetrain!