SLP 421 Bobcat GTO

Filed in Pontiac GTO by on September 16, 2017 • views: 183

Nicely integrated and fully functional intake slits on the SLP hood give a hint to the hidden power of this Goat.

“This thing really shines on the winding roads, and there’s nothing like rowing through the six-speed while listening to the rumble of the exhaust.” -Robert Hamblen

Back in the ’60s—a decade marked by the civil rights movement, free love, and of course the musclecar—there existed a very special Pontiac dealership in Royal Oak, Michigan. Owned by Ace Wilson Jr.—a name befitting a fighter pilot or a true car-guy, Mr. Wilson’s Royal Pontiac offered some of the fastest, best performing, and most-sought-after Pontiac GTOs of the era.

Even before the appearance of the GTO option on the ’64 Lemans, Royal Pontiac offered special tuning packages to improve upon the already impressive performance of Pontiac’s 389ci and 421ci engines.

Customers could either purchase the go-fast goodies for the do-it-yourselfers, or choose to have the dealership do the wrenching.

SLP Bobcat Pilot Car Number One’s owner, Robert Hamblen, has owned the car since 2005. That proud grin on his face tells us he probably won’t sell anytime soon!

The name given to the modified cars was “Bobcat,” born from combining letters from Pontiac’s full-size Bonneville and the Catalina. Using tried and true hot-rodding techniques, the Royal Bobcat cars were massaged by advancing spark at the distributor and increasing the timing at high rpm to make more horsepower. A thinner copper head gasket was used to raise compression and various performance parts were added, equating to an additional 30-50 horsepower.

The Bobcat package also included a lower-restriction air cleaner, open hood scoops( as applicable) a Ram Air pan, richer carburetor jets, a 0.27-inch head gasket (held over from Pontiac’s Super Duty era), and weaker springs in the distributor (36 degrees all in by 2,400 rpm). Nicely integrated and fully functional intake slits on the SLP hood give a hint to the hidden power of this Goat.

As popularity grew and the GTO roared towards 1970, suspension pieces and unique paint schemes were added making the Royal Bobcats stand out from the crowd; even stuffing a hopped-up 428 ci. ‘plant into the midsize Goat was not uncommon.

Forty years after the first GTOs made their mark on the streets and muscle-car folklore, Pontiac was ready to bring the Goat back to its former glory. Although Royal Pontiac was a thing of the past, many tuning companies thrived in the new age of computer controls and electronic fuel injection.

Best known for its Firehawk packages adorning the Fourth-Gen Firebird Formula and Trans Am, SLP (Street Legal Performance) of Toms River, New Jersey, saw the opportunity in supplying its proven performance parts and old-school hotrod know-how to the new Goat. In honor and recognition of the past performance prowess of the Royal Pontiac-modified vehicles, SLP chose to introduce their own Bobcat performance package for the new ‘04 GTO. But more on that in a minute…

The SLP progressive rate lowering springs provide a nasty-low road-hugging stance.

Early in 2005, Robert Hamblen of Wayne, New Jersey, was in the market for a used ’04 GTO. A long time Goat aficionado and member of the Garden State GTO club, Robert wanted the new model for more “regular use” in place of his ’70 GTO. Being a GTOAA club member, Robert had built a friendly relationship with Jim Salerno, a GTO fanatic, who was also the owner of Jim Salerno Pontiac in Randolph, New Jersey.

Robert mentioned to Jim that he was looking for a preowned, yellow ’04 Goat and to keep him in mind. Robert had little confidence that such a rare car would be available used after only a year’s production, but his shallow pockets ruled out the purchase of a new one.

As fate would have it, Jim Salerno contacted Robert by the Fall of 2005 with some interesting news. A very special yellow ’04 GTO was available from SLP and was being offered for sale through Salerno Pontiac. Intrigued, Robert was told of the brief, yet important, history of this particular Goat. From 2004 to 2005, SLP used the GTO as a test mule for their 421 Bobcat package and a host of performance parts.

421 Bobcat Badges and pilot-car numbering display the rarity of this Goat.

SLP and other specific logos and decals adorn this car, lending to its one-off collectibilty.

421 Bobcat Badges and pilot-car numbering display the rarity of this Goat.

With the 421 denoting crank-rated horsepower (not cubic inches like in the old days), pilot car No. 1 (experimental car X03) was fitted with various engine, exhaust, and camshaft combinations, including SLP’s short block ZL-402 topped with LS6 heads, a FAST intake (although a stock LS6 piece appears in our photos), six-piston Wilwood brakes, various suspension pieces, and a custom tune.

As much as the cynical types like to declare how the GTO was an Australian built machine, and not a “true American car,” GM never kept that a secret. There are a few locations throughout the car that point that fact out.

The mule Goat was thoroughly flogged on tracks from Michigan to Englishtown during the R&D stage of its life, but was now ready to be released from service and sold. For $10,000 less than the price of a brand new, standard GTO and the 421 Bobcat goodies for “free,” Robert signed on the bottom line and took possession of his super rare new-age Bobcat GTO.

Robert quickly fell in love with his neo-Goat’s power on tap and road-race–handling abilities. Even in standard guise, the muscle coupe proved a match for even the priciest competition from Europe and Japan. Robert loved the puzzled looks he would get from many a BMW owner. The 421 Bobcat bolt-ons only added to the impressive traits of the new GTO. Robert says he “loves to turn the key and feel the car shake to life.” He also likes the much-maligned sleeper styling of the ’04 GTOs, saying, “They are not over the top.”

A peek of header tubes and a “baseball bat thick“ strut tower bar are the only departures from the factory LS1’s appearance.

Robert’s GTO came equipped with it’s original 5.7-liter LS1 still factory fresh with only 50 non-test miles. 421 Bobcat options include – a deeper breathing SLP Blackwing air filter, 85mm mass air sensor and a 160-degree thermostat. Providing increased valve opening duration are 1:85 ratio rocker arms with 1.255-inch springs and titanium retainers.

Freeing up extra horses while limiting parasitic loss is an SFI-certified 25% underdrive crankshaft pulley. Exhaust duties are handled by stainless steel 1 3/4-inch primary longtube headers with 3- inch collectors flowing freely through an X-pipe, Loudmouth II modular catback, and exiting with purpose and raucous abandon from twin, slash-cut stainless tips. Engine management is dialed in by a custom SLP tune and all six forward gears are engaged through a B&M shifter.

Still appearing and smelling new, the cockpit remains stock, featuring color- coordinated gauges, beautiful GTO embroidered seats and ample Blaupunkt sound.

Benefiting from this car’s unique beginnings, Rob’s Goat acquired some very choice suspension upgrades present but not directly part of the Bobcat Package; including a stronger strut tower brace, progressive rate lowering springs with rear camber kit and heavy duty rear sway bar with higher durometer bushings.

Also present, a lightweight aluminum skid plate and line lock kit hinting to the hard core set ups from the cars test and tune days.

Over the past decade, Rob has reveled in his Goat’s grand touring prowess, taking the yellow GT car on many long and pleasurable road trips. Whether cruising to upstate New York with his lovely wife Victoria, rolling into Oktoberfest at Hunter Mountain, stalking the local cruise night, making a ground shaking appearance at the steakhouse or attending regional GTO shows, the driving excitement has been immeasurable.

Besides it’s bright yellow cloak, the new-age GTO is a sleeper to be sure, with very understated yet attractive looks – similar to the original ’64 Tempest/Lemans cars.

Rob says, “This thing really shines on the winding roads, and there’s nothing like rowing through the six-speed while listening to the rumble of the exhaust.”

Becoming a dad and running his successful A/C company definitely cuts into the time he’d like to be putting the GTO through it’s paces, so Rob cherishes every chance to get his Goat out of the garage and on the highway to really stretch it’s legs. “Putting the hammer down really makes you feel like the King of the road,” Rob continues, “and isn’t that the whole point?”

Rob has shared his passion with his dad, now 82, driving up to Vermont for visits to cruise in the mean-spirited sport coupe; and has introduced his four year-old son Alexander to the loud yellow machine-indoctrinating the next generation GTO fan.

As caretaker of this one of a kind musclecar, Robert has done a great job keeping the 19k-mile Goat in near-mint condition. Rob has no plans to change or add anything to his modern factory hotrod, a testament to its rarity and SLP’s expert touch.

Looking like a stock ’04 GTO, there’s not much letting the Bobcat out of the bag.

There can be little doubt, that like the Royal Bobcat cars from Pontiac’s heyday, Robs SLP Bobcat GTO is destined to have it’s day in the sun as a timeless American muscle classic. In the meantime, Rob plans to enjoy his rare and powerful beast to the fullest.

Tech Sheet:

  • CAR: 2004 SLP Bobcat GTO Pilot Car
  • OWNER: Robert Hamblen
  • ENGINE BLOCK: Stock, LS1
  • CRANKSHAFT: Stock, LS1
  • PISTONS: Stock, LS1
  • CAMSHAFT: Stock, LS1
  • CYLINDER HEADS: Stock, LS1 (1:85 ratio rocker arms, 1.255-inch springs and titanium retainers)
  • COMPRESSION RATIO: 10.1:1
  • INDUCTION: SLP 85mm MAF, SLP Blackwing air filter
  • IGNITION: Stock coil packs, MSD plug wires
  • EXHAUST: SLP 1-3/4 inch long-tube headers, X-pipe, Loudmouth II catback
  • FUEL DELIVERY: Stock
  • OILING: Stock
  • TUNING: SLP
  • TRANSMISSION: Stock, T-56
  • CLUTCH: Stock
  • DRIVESHAFT: Stock
  • REAREND: Stock
  • SUSPENSION: SLP/various components
  • CHASSIS MODS: None
  • BRAKES: Wilwood 6-piston
  • WHEELS: 17×8 GTO
  • TIRES (street): Stock; 245/45/17
  • HP/TQ.: 421/420 (flywheel)


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