In my last experience with an SLP test car I remember being pinned back in the seat every time I so much as breathed on the throttle. The ZL-402-powered '04 Goat had the ability to send any gearhead reaching for a cold shower, but where last year's effort tended to be a little rough around the edges, the '05 GTO proved silky smooth. Equally at home on the street, the track, and even a road course, the 3,800-pound Poncho was the perfect balance of power, handling, and drivability.
For 2005, SLP started with the LS2's capable 364 cubes and added the 455 Bobcat Performance Pac (P/N 29042). The comprehensive kit consists of high-flow 3-inch cats, an X-pipe, and a PowerFlo 2.5-inch cat-back dual exhaust. SLP designed more traditional 1.75-inch- coated long-tube headers with four-into-one-style collectors on the GTO for a cleaner and easier fit, rather than having to go through the steering shaft, according to Director of Engineering, Brian Reese. Enhancing the LS2's modest cam is a set of 1.85 ratio rocker arms, 1.255 valvesprings, and titanium retainers. A custom tune was developed for this package on the dyno, which is uploaded with a Diablo Sport programmer. A high-flow air filter, a 25 percent underdrive balancer, a 160-degree thermostat, and 455 Bobcat badges are also part of the deal, helping to coax the Gen IV mill into nearly 400 rear-wheel horsepower and 400 lb-ft of torque (or about 455 hp at the crank).
After having spent a few weeks prior in our bone-stock project '05 Goat, the power and sound were the first most obvious observations. The SLP-tuned GTO was much crisper in throttle response and overall acceleration, as the sluggishness that results from be riddled with an 11.8:1 air/fuel ratio had been eradicated at SLP's state-of-the-art facilities. Fuel mileage had also noticeably increased, especially in North Jersey stop-and-go traffic. The increase in overall efficiency could also be accredited to the slew of bolt-ons, which also provides a rewarding sense of satisfaction as you feather the throttle and clutch out of the hole, proceeding to row through all six gears of the T-56. For normal driving, the tremendous torque made Second gear useless, and I found myself not wrestling with the skip shift. Spirited driving, on the other hand, rewarded the driver with power ample enough to spin the tires at will, but not so much that it was overpowering. On the street and as a daily driver, you couldn't ask for a better combination.
There were few challengers at stoplights on the highway, but the few who did realized very quickly that they could neither match the Goat's grunt down low nor its power upstairs. With so much torque you'd expect the power to start leveling off, but it doesn't--it just keeps pulling. The bark from the PowerFlo mufflers (which are the most docile of SLP's three muffler choices) and long-tube headers seemed perfectly fitting, not only for a car this powerful, but for a car as refined as the GTO. At constant speed or moderate acceleration you could scarcely tell SLP's from the stockers, but at full or part throttle the sleeping giant awakes, unleashing a fierce battle cry. Everywhere I went, Corvette and even Mustang owners complimented the Goat's deep timbre. The healthier valvetrain and higher-ratio rockers combined with the long tubes also made a slightly lopey idle. The only negative comment I can make about the exhaust system is that there was some droning on the highway under 2000 rpm, which in Sixth gear is below 80 mph. But the transmission and motor did not like this rpm in Sixth gear anyway, as it seems the transmission is lugging the clutch.
Speaking of clutches, another reason the Goat was so pleasant to drive in stop-and-go traffic was the silky-smooth LS6 clutch package with a lightweight flywheel (P/N 60026). The pedal feel and effort was even better than stock, without feeling brittle (or smelling burning clutch after pedaling from a standstill on a steep hill). There were no drivability issues whatsoever with the car--no overheating, and no problems charging the battery from the underdrive pulley, either. Despite the sweltering humidity of the New Jersey summer, the Goat ran exactly like a new car should without mods, only with a whole lot more to offer.
Unlike even our SAP-equipped project car, SLP's GTO came with a set of dealership-optioned forged 18x8-inch rims made by MCSQUARE Inc. The wheels were given to dealerships, such as Jim Salerno Pontiac in Randolph, New Jersey, where SLP got the car, to help promote sales of the Aussie-born Goats in late 2004. This addition is a large part of the reason the car received so much adulation during my temporary occupation. Everyone from gas station attendants to a father in a minivan was impressed by the look and sound of the SLP-tuned Goat. Complementing the wheels were a set of high-performance Toyo Proxes 245/40/18 rubber that were noticeably more grippy than the stock all-weather tires.In addition to the stickier rubber, our test car had SLP's full line of suspension components, including the lowering springs and camber kit that drops the Goat about 1-inch, while still keeping the tricky Aussie suspension in line. SLP uses a progressive-rate spring that, while stiffer than stock, does not degrade the ride quality. To someone who is used to driving a lowered solid-axle car, the ride was as smooth as glass. However, since the suspension travel is limited, it is much easier to bottom out the shocks, as I found out traveling through scenic Newark. The decorative factory strut tower brace was also upgraded with SLP's heavy-duty mild steel brace, adding legitimate strength to the frontend. Located on the bottom end of the suspension were SLP's poly bushings and rearend links (P/N 73006), which take the flex out of the factory sway bar's rubber bushings.
Though the stock GTO handles very competently from the factory, thanks to its independent rear suspension (not to mention Cadillac-smooth ride quality), it often suffers from the dreaded IRS wheelhop. SLP smartly designed an adjustable rear sway bar and poly bushing kit (P/N 73004), which quite effectively keeps the rearend from bouncing like a basketball under hard acceleration. A side effect from the thicker sway bar and stiffer bushings is that it removes a great deal of the body roll and understeer found in the soft factory suspension. Despite the GTO being limited to a small tire size because of its tight wheelwells, with the thicker sway bar, it can hang with the best of them. Overall, the car feels much more nimble than its size and weight would indicate. The car goes where you point it and doesn't make you work for the performance. It feels extremely stable, predictable, and confidence-inspiring. Even near its limits, you still feel in control.
On the highway, some patchouli-smelling, Starbucks-drinking Eurotrash arrogantly assumed his $50,000 M3 would easily overtake the Goat while making a left turn at a stoplight. Despite the M's 80-foot lead, the GTO dusted the Beemer, and the LS2 barely broke a sweat. As we headed toward a long sweeping left-hander onto another highway, I eased into the '05 GTO's 12.6-inch twin-piston binders pushing the weight onto the front tires. With both hands applying smooth and even pressure, I then eased into the turn as I let off the brakes. The body weight settled onto the right-side tires without a yelp of protest, despite carrying a lot of speed through the turn. As the road and the car straightened out, I looked in the mirror before getting back on the throttle, and the M3 was barely in sight.
A tight schedule prevented us from hitting the road course to translate this experience into some quantifiable numbers, and we only made two passes in it at Englishtown during our supercar shootout. The hot and muggy afternoon at the tail end of the New Jersey summer confined the finely tuned LS2 to a still-impressive 12.74 at 109 mph, five-tenths faster than our stocker went. With a little more seat time and some more favorable weather, these figures could easily have been improved. Zero to 60 times also dropped to 4.8 seconds, whereas our stock '05 managed only 5.54 the very same day. According to other magazine tests, stock M3s accelerate to 60 in exactly the same amount of time, despite carrying over 400 less pounds. However, where the M3 plateaus at around 13.6 in the quarter, the 455 Bobcat keeps pulling. And it is this top end power and flat torque curve that makes this Goat so much more fun to drive.