Griggs Racing: The Market is Cornered on Custom ‘Stangs

A $150,000-plus Porsche pulls up to your right at a quiet stoplight. You’re in your Griggs Racing GR40 ST and could extend a kowtow nod: After, all, you’ve been challenged by supposedly superior European automotive force.

Instead, your custom Mustang smokes the classy Carrera. Next stop, the Porsche is ready with all six gears and hand-stitched leather upholstery. You deliver a smoke show again. Then, to show that your GR40 corners at the highest levels as well, you take a tight freeway onramp and kick Griggs’s g’s in his face as well.

This is Bruce Griggs’s dream come true — and the exotics-stinging reality his customers thrill to daily. His Sonoma, Calif.-based Griggs Racing designs, develops and fabricates high-performance Mustangs. He and his small team of professionals can transform your legendary American ponycar into a stallion equal to any on the track or street.

“Our cars are known for ease of use, simplicity and a forgiving nature while run at the limit,” says Bruce, with 30 years of racing and build experience. “Their overall performance and driving experience is far, far superior to anything near their price points.”

Zero to World Class Fast — And Affordably

If you have a 1964 to 1970 Mustang or 1979 to current version, Bruce will make it perform with the world’s finest GT cars. For instance, his cars throw lateral “g” forces of 1.4 (about 40 percent more intense than standard Corvette Z06s, Vipers or Porsches) — and do so with a confident and supple ride.

Three basic stages are available: the GR40ST (Street), GR40TT (Track), and GR40RT (Race) — the last for track and race. All are superior handling vehicles. For his builds, Griggs uses Ford V8s — 5.0/5.8-liter and 4.6/5.4-liter based. Sometimes, requirements dictating, he installs LSX-based engines.

Tom Wilson, tech columnist for “Road & Track,” writes of this transformation, after test-driving a GR40ST: “It’s a revelation to anyone experiencing the joy of piloting a precise, spirited chassis for the first time, or to the old hand who didn’t expect such excellence from a heavy powerhouse such as the Mustang.”

Griggs Racing can make you world class without making you world-class poor. For instance, the starter GR40ST is $49,900, and the GR40TT costs as high as $90,000 for a fully optioned car with a Kenne Belle or Paxton supercharger. The race-only RT is built to customer’s specs and priced accordingly.

Bruce is a racer from his youth — and an engineer almost as long. He started quarter-midget racing when he was 8 and later attended Cal Poly SLO for engineering school. He served as an Air Force flight engineer on a military version of a Douglas DC-6 in Viet Nam. During college and his Air Force days, he raced and built suspension and chassis components, mainly for Mustangs. His ’89, “Old Blue,” is the most victorious single Mustang in road-racing history.

He founded Griggs Racing in 1979, Griggs Racing Products in 1992 and GR40 Cars in 1996. “Our slogan, ‘Champions Made Here,’ is not rhetoric but supported by historical fact,” Bruce says.

Mustangs in Touch with Their Wild Side

For the GR40ST, Bruce and crew raise the stock 300 horses of the 4.6-liter, three-valve SOHC to 368 at 6000 rpm through computer tweaks and a 2.5-inch stainless steel dual-exhaust system. He retains the already strong standard ratio 5-speed, fully synchronized tranny, but you can select a 6-speed manual. You choose from a variety of final gear ratios, 3.55 through 4.10, and can add a torque-biasing differential as well as a billet-aluminum quick shifter.

If you want power beyond natural aspiration, the superchargers add 11 psi to the induction system, increasing horsepower to 547 at 6500 rpm and 463 pounds of torque at 5700 rpm. Supercharger installations include an over-running clutch and air/air charge cooler. All Griggs vehicles are dynoed and tested before delivery and carry a limited three-year/36k powertrain warranty.

“What you have with this is a street-legal Mustang that looks very much like a stock GT but is now apples and oranges different in timed performance and handling,” Bruce says. With supercharged versions, 0–60 mph times are in the world-class three-second range and top speeds near 200 mph.

The GR40ST transformation includes an aluminum dual-core radiator and surge tank and a fuel-system upgrade as well as A pillar-mounted gauges for precise engine monitoring.

You can option, too, with a high-capacity road-race oil pan, oil cooler with remote filter assembly, stainless long tube headers with offroad x-pipe and various high-performance exhaust cat-back systems. Inside, add an integral roll bar, a supercharger gauge pack (boost, fuel psi, and oil temperature) and safety equipment such as a six-point racing harness and CNC aluminum road race seats. There is even an optional multi-channel data acquisition system.

Griggs Racing cars handle with the track-savvy precision of track cars yet deliver the comfort of exotic luxury cars, too. “I long ago realized that I had to redesign the entire system to achieve the kind of performance, reliability and safety I wanted,” he says.

The GR40 SLA suspension includes components such as a tubular front cradle with integral core support; adjustable bind-free anti-roll bar; severe duty front lower control arms; a heavy-duty TorqueArm™; adjustable Panhard bar assembly; adjustable rear lower control arms; and a Koni coil-over suspension with double wishbones. These components eliminate go-fast distractions such as wheel hop. Further refinements come with options such as double-adjustable coil-overs, a Watts link with adjustable roll center, and a race-tuned steering rack.

Despite the hardware, Griggs’ customers attest to the superior ride quality of the vehicles. Wilson writes: “The car points into the corner with enthusiasm and carves right down to the apex with a light, precise, linear feel to the steering. This authority is even more appreciated in mid-corner, the place where the stock steering goes vague and responds slowly and unevenly. Here the GR40 front suspension, its tires flatly planted to the asphalt, answers with immediate, precise corrections.”

Wilson adds: “Also unexpected is the incredibly civil ride from the GR40 suspension. It feels as plush as the stock suspension, and in the bumps when trying hard, even more so. The combination of stiff chassis and accurate, correct GR40 suspension geometry means we can let the wheels move up and down, which in turn delivers a ride that’ll please the fussiest daily commuter.”

Wheels are 18×10-inch alloys, and you choose from 275/35 series tires to Toyo Proxes 305/35 series (10.5-inch-wide wheels) or Hoosier 315/30 A6 or R6 rubber. Once again, you can option widely, including high-performance brake pads and one-piece forged aluminum wheels. You can also add a front spoiler and rear wing as well as lightweight body panels and high-downforce, low drag, carbon fiber wing and front splitter.

Wilson: “The car tracks so honestly right up to the limit, and has such gentle manners as the tires sign off that you’ll be ready for more grip. It’s that good.”

The brakes for the GR40 and other Griggs Racing cars are particularly noteworthy. “Besides reducing unsprung weight, these brakes offer a new level of precision in the brake pedal,” Wilson writes. “This is especially true in the brake release, an area where stock brakes are absolute dullards.

“The 4-on-4 brakes let go of the discs with the same sensitivity they apply them; on open track day that means slowly coming off the brake in perfect confidence while the tail end — so expertly controlled by the GR40 gear — rotates magnificently outward as much or as little as you wish. The transition from threshold braking to the throttle while holding the car at the limit has never been so rewarding.”

Offered exclusivly at Anthem Motors, 623.879.0930. Experience the GR40 for a limitied time at the Vanhorssen Group, 888.287.6149. Griggs Racing,, 707.939.2244