When most Pontiac fans think of blown GTOs, images from the mid '60s of GTO match racers driven by Don Gay, Dick Jesse, Arnie Beswick, and others are likely to come to mind. However, the world's a different place now, a better place where superchargers and street driving go hand in hand and heavy GMC 6-71 huffers are replaced by compact yet capable Eaton blowers which fit underhood and are invisible to prying eyes.
Today, Magnuson Products leads the charge (literally) in the supercharged GTO arena with its brand new MagnaCharger kit for the '04 GTO. Completely emissions-legal in all 50 states and happy to sip 91-octane unleaded, we watched as the stock GTO output rose from 262 hp at 5,250 rpm and 286.2 lb-ft at 2,750 rpm to an amazing 386.7 hp at 5,500 rpm and 420.2 lb-ft at 3,250 rpm on Magnuson's in-house Mustang chassis dyno.
Though our Arrowhead Performance test car was stone stock for the baseline chassis dyno test, the exhaust system had been replaced by a Spintech dual-cat, side-exit off-road system by the time the blower was installed (see our September '04 issue for the Spintech story, "True Duals for the New Goat"). Without the free-flowing exhaust, we'd bet the power numbers would be down a small amount, but not enough to make a huge impact on rapid forward mobility. Remember, the factory exhaust manifolds were still in place.
A quick test drive in our huffed test car yielded much improved acceleration in every gear over the GTO's already impressive capabilities and a satisfying blower whine at medium throttle that mutated into a banshee wail when the pedal hit the floor. The beauty part is how the blower is nearly silent until your right foot calls it out to play. Then its 6 pounds of boost require extra care to prevent tire spin at throttle openings the stock GTO can normally handle without any risk of lost traction. Are we complaining? No way. However, slicks will be the order of the day at the strip. On the freeway, the extra torque makes the 5.7 feel like it's grown an extra liter of displacement and you can pass just about anything you're likely to encounter.
We pulled some strings to bring you this exclusive behind-the-scenes look at how Magnuson adapted its famed Eaton-sourced lung to the new Goat's 5.7L Gen III mill.
PROTOTYPING THE GTO
Magnuson designs, develops, and produces bolt-on supercharger kits for a wide variety of late-model applications. Every one of these packages goes through a lengthy prototyping and fabrication process before production-ready units hit the streets. The new GTO is no exception. While Magnuson offers several MagnaCharger kits for vehicles equipped with the General Motors Gen III engine, the unique packaging of the 5.7L LS1 powerhouse in the Holden Monaro-sourced GTO required some adaptation. Here's a rundown of how Magnuson's team overcame the hurdles.
 How cool is this...the Holden...  How cool is this...the Holden plant sent this wooden hood clearance template to aid with packaging the GTO blower kit. The sharp hood slope looks great but forced Magnuson to reduce the jackshaft drive pulley diameter from 3.5 to 3.0 inches for hood pad clearance. Proper blower speed is restored by juggling the drive ratio of the pulleys at rear of the blower. |  Each MagnaCharger is shipped...  Each MagnaCharger is shipped in pre-assembled, pre-sealed form, ready for installation. Of course, you will need to strip the stock induction as shown here. Blue tape was used to prevent engine contamination during the lengthy prototyping process and obviously must be removed before final assembly. |  The off-center location of...  The off-center location of the GTO air cleaner assembly required a redesigned air inlet tube. This wooden mockup pattern will be used to generate roto-molded plastic tubes to solve the problem. Note the compound curves in the pattern to suit the low hood line. The new tube uses a D-section to minimize pumping losses and maximize airflow to the stock throttle body, which is retained. |
 An initial obstruction was...  An initial obstruction was contact between the supercharger drive jackshaft and the passenger-side engine cover. |  A similar contact problem...  A similar contact problem arose on the driver-side between the engine cover and the boost bypass actuator unit. GTO owners can retain originality if they choose; Magnuson will include templates in production GTO kits to serve as guides for trimming the plastic covers for clearance. |  Here, the finger points to...  Here, the finger points to one of several raised bosses, on the stock GTO knock sensor plate, which cause interference with the underside of the MagnaCharger intake manifold. Rather than forcing customers to machine the plate, Magnuson supplies a redesigned plate (shown here in place on the engine) that solves the conflict. |
 The Magnuson knock sensor...  The Magnuson knock sensor plate (left) also incorporates a redesigned PCV breather labyrinth that relocates the stock topside PCV tube beneath the plate for added supercharger unit clearance--all this just for a measly 0.200 clearance gain! The stock knock sensors are reused. | | |
INSIDE THE MAGNACHARGER
Most enthusiasts take a quick glance at the MagnaCharger and assume it's a miniature version of the venerable GMC 71-series supercharger. Not so! While the iconic GMC diesel huffer set the pace, MagnaChargers are dry flow units (gasoline is injected at the ports) and feature integrated intercoolers. Best of all, MagnaChargers are emissions legal for late-model muscle machinery and are priced at $5,995 in natural aluminum finish or $6,995 for the sexy polished job shown here. Let's look at what makes the MagnaCharger tick. Remember, you ordinarily won't see this stuff, as all MagnaCharger kits come fully assembled and ready for easy installation.
 These are the inner workings...  These are the inner workings of the Magnuson MP112 fifth-generation supercharger with its efficient 60-degree helix rotors. An internal bypass valve is controlled by the black vacuum motor at the rear of the case. A Magnuson development, the bypass actuator opens the bypass at light-throttle cruise conditions so no boost is generated. In this mode, the supercharger "naps" and requires less than .5 hp to drive to preserve excellent fuel economy and reduce wear. However, when it senses more than 4 inches of vacuum (not manifold vacuum), the actuator closes the bypass, boost production begins (5 to 7 pounds), and rear tires start smoking. The actuator is extremely sensitive and can toggle open or closed in less than a half second. |  The underside of blower reveals...  The underside of blower reveals a generous boost outlet passage. |  Six bolts fasten the cast-aluminum...  Six bolts fasten the cast-aluminum plenum chamber top cover to the blower. |
 The patented MagnaCharger...  The patented MagnaCharger air-to-liquid intercooler controls the airflow and water flow rates to effect a 50-degree drop in charge inlet temperature. This enhances fuel density, but perhaps more importantly, allows the engine computer to tolerate more aggressive ignition timing before the knock sensors activate. Magnuson testing has shown at the threshold of pre-ignition, 1 degree of timing can be worth as much as 30 horsepower, thus the emphasis on preserving ignition timing rather than making maximum boost. Its Bosch electric coolant pump is the same type that has been certified for use in numerous OE applications. The intercooler system holds 1 gallon and uses a 50/50 mix of Dexcool and deionized water. |  The intercooler fits into...  The intercooler fits into to the plenum cover, and the inlet and outlet nipples fit into drilled passages. |  Then a stamped aluminum separation...  Then a stamped aluminum separation plate is positioned to isolate and immobilize the intercooler. |
 Finally, a cast-aluminum plenum...  Finally, a cast-aluminum plenum base "tub" bolts to the plenum top plate and sandwiches the intercooler. |  Assembled, the MagnaCharger...  Assembled, the MagnaCharger stands ready to force-feed the Gen III's trademark "cathedral" ports. |  A precision-machined jackshaft...  A precision-machined jackshaft rides on low-friction bearing mounts, takes power from the front of the engine, and transfers it to the rear of the engine to run the blower. This ingenious blower drive system eliminates the need for massive reworking of the stock crank-driven engine accessories. |
 The jackshaft drives pulleys...  The jackshaft drives pulleys at the rear of the blower (by the firewall) that can be manipulated to adjust boost levels. Each MagnaCharger unit comes with larger 42-lb/hr injectors installed. |  Here's the finished installation...  Here's the finished installation on the Arrowhead Performance GTO. We've got to admit, while the plastic coil covers may look a little cheesy to some with the stock GTO intake manifold, they really look great with the blower and give the engine a broad-shouldered look. Suddenly, we dig 'em. The intercooler reservoir (left) perches atop the battery on a special bracket (included in kit). | |
GOAT POWER FROM DOWN UNDER
By now every GTO hobbyist knows that the '04 GTO is powered by the rompin', stompin' LS1 motor. However, it isn't just a quick slam dunk and g'day using an existing F-car (Camaro/Firebird) or Y-car (Corvette) mill. Rather the LS1 used in the Holden Monaro CV-8, er, um, Pontiac GTO, has many specific features to match the chassis architecture of its Aussie host.
 Thanks to deep factory connections,...  Thanks to deep factory connections, Magnuson scored a GTO mill to assist in the design of its supercharger kit. The stock 5.7 engine is factory rated at 350 flywheel hp and 365 lb-ft of torque, but that's only the beginning, baby. |  The cast-steel exhaust manifolds...  The cast-steel exhaust manifolds are unique and feature long, sweeping runners that bear an uncanny resemblance to Pontiac 421 SD manifolds of yore. Unfortunately, they aren't aluminum. The shiny stamped heat shields cause the illusion. |  As with all domestic LS1 engines...  As with all domestic LS1 engines built since the '02 model year, an LS6 intake manifold is used on the GTO, which has a larger plenum volume than '98-99 F- and Y-car LS1 intake manifolds. |
 The GTO retains the LS1's...  The GTO retains the LS1's 73mm throttle body, which is reused along with the MAF sensor in the MagnaCharger conversion process. |  To bolster the GTO theme,...  To bolster the GTO theme, molded plastic covers hide the coil-on-plug ignition. Love 'em or don't; they're likely to be highly collectible down the road, so don't trash 'em. |  This cast-aluminum oil pan...  This cast-aluminum oil pan is a GTO-specific front sump design to clear the K-member. A matching pickup tube is used. |
 The power steering pump bolts...  The power steering pump bolts directly to the driver-side cylinder head rather than to a bracket as on F- and Y-car applications. The pulley diameter also differs from any domestic LS1 application. |  A unique steel bracket locates...  A unique steel bracket locates the plastic power steering reservoir above the steering pump. | |
PROVE IT ON THE CHASSIS DYNO
The MagnaCharger people claim their kits generally add 20 rear-wheel hp per pound of boost. Proving the point, they strapped the Dan Long-owned Arrowhead Performance GTO to the Mustang chassis dyno and delivered an additional 124.7 hp and 134 lb-ft of torque. Yes, a Spintech off-road, side-exit exhaust found its way into the mix before blower testing, but even with a stock GTO exhaust system, the MagnaCharger kit is sure to put any GTO over the top. Lighter F- and Y-cars won't be a problem...unless they too are MagnaCharger-equipped.
After observing Dan Long's Spintech, MagnaCharger-equipped GTO on the Mustang chassis dyno, another MagnaCharger-equipped six-speed GTO was put in its place and flogged. This second GTO lacked the quasi-legal dual-cat Spintech H-pipe and side-exit exhaust. Instead, it was fitted with an aftermarket true 50-state-legal, stainless steel, dual-outlet catback exhaust system from another company. The best peak power level generated in two back-to-back dyno pulls was within 10 hp and 10 lb-ft of the first GTO test car. After this demonstration, any concerns that the first GTO's gain was a fluke were put to rest.
 The included SuperChips Power...  The included SuperChips Power Programmer plugs into the computer diagnostic port under the dash. Just follow the prompts and it automatically recalibrates shift firmness (automatic cars), torque management, ignition, and fuel curves in less than five minutes. |  Our test car is the Arrowhead...  Our test car is the Arrowhead Performance GTO. Contact Arrowhead for wheels, hoods, graphics, and other goodies to personalize your GTO. |  Here are the "before" and...  Here are the "before" and "after" horsepower and torque readings on the Mustang chassis dyno. |