Grubb Worm: Get To Know the World’s Fastest Manual in Drag Racing

Going from 0 to 216 miles per hour in 6.6 seconds is amazing in any car. Doing it in one with a clutch pedal and an H-pattern shifter is epic.

It all looked good when Jonathan Atkins lined up his 1997 Camaro Z28, called "The Grubb Worm," next to a highly modified Chevy S-10 pickup in front of 15,000 fans for the semifinal stick-shift-class drag race at Maryland International Raceway. Just as the Camaro's 2,000-horsepower (hp) single-turbo V8 reached launch-boost before the tree counted down, it stalled. Atkins watched his competitor rocket away. The world's quickest H-pattern stick-shift car was out.

When the limited-edition (684 built) 30th Anniversary Z28 first started its life, it came with a special orange-stripes-over-white paint scheme, a six-speed manual, and a 285-hp 5.7-liter LT1 V8 engine, making it capable of a 14.2-second quarter-mile at 100 miles per hour. It's undergone a number of modifications since then, but Grubb Worm still has its factory clutch pedal, brake, and accelerator pedals.

Today, it's the stuff of legend to the 52,000 people who attended the Haltech World Cup Finals at Maryland International Raceway last November, and to millions more who’ve seen it on the internet. The annual World Cup Finals is the biggest import vs. domestic drag race on the planet, and the 350 largely street-based cars that enter from 36 states and seven countries make it one of the most important events in drag racing period.

The crowd is boisterous, uproarious, fun. Fans wave Puerto Rican, Canadian, and American flags. They cheer or boo imports like Toyota Supras or domestics like Ford Mustangs. They bet hard-earned cash on race after race. When Grubb Worm comes to the line, revs up, and launches—issuing flames and concussive booms with each shift as it goes down-track—they go absolutely nuts. They roared when Atkins clicked off a 6.82-second quarter-mile pass, making him top qualifier in the stick-shift class.

"It's the best race," Atkins says in a relaxed North Carolina accent. "All the fastest guys come. The weather's always cool so you know you’re going to go fast."

Atkins rightfully expected to go all the way at the World Cup Finals. At a race in Florida the month before, he’d made the finals, too, but Grubb Worm came up short, losing to a modified big-turbo fourth-generation Toyota Supra. The loss hurt, but earlier in the event, Atkins set a world record for a street-car-based manual-shift car: He ran the quarter in a breathtaking 6.61 seconds, crossing the finish line at 216 mph.

Going from 0 to 216 mph in 6.6 seconds is amazing in any car. Doing it in one with a clutch pedal and an H-pattern shifter is epic.

The Worm Turns

A North Carolina performance enthusiast by the name of Randy Grubbs first bought Grubb Worm when it was brand-new. By 2007, he wanted more from the stock Camaro, and brought it to Atkins’ company, Tick Performance, which specializes in GM performance modifications, including transmissions. Grubbs asked Tick to make it a hot street car, and Atkins complied, adding high-performance cylinder heads, a camshaft, and a nitrous kit to the stock LT1. When Grubbs asked Tick to take it up a notch, Atkins sourced another LT1, added an 80-millimeter turbocharger, plumbed it to run on E85 ethanol, and threw on 15-inch wheels with drag radials. "It was reliable and made 900 horsepower," Atkins tells Popular Mechanics. "It became my favorite customer car."

Aktins was drag racing other cars, but he liked the Z28 so much that he bought it from Grubbs in 2017. The first thing he did was take the 3,600-pound street car to a standing half-mile event at Stanly County Airport in Albemarle, North Carolina. The Tick Performance crew changed the rear-end ring and pinion gears for higher top speed, and headed for the runway.

"I didn't even really know if the engine would survive for half a mile at 900 hp," Atkins recalls. "It went 180 mph, and drove itself back into the trailer. It blew us all away."

The car ran so well, Atkins couldn't resist taking it to the drag strip. He raced it a few times before putting it on a diet. The new "Grubb Worm"—a play on Grubbs’ name and the white-and-orange coloring of grubb worms and the Z28—got Lexan (plastic) side and rear windows, a fiberglass rear hatch, and other weight-saving treatment. While it lost several hundred pounds, it still had a streetcar-like diaphragm clutch, and could still be driven as a daily . . . that could rip off 8.80 elapsed times.

By 2019, Atkins made it a race car, completely gutting the interior, ditching the cooling system and alternator, and adding a 7-second-certified roll cage, a four-link rear suspension, and an 8-inch, twin-disk, six-lever slipper clutch. "It's a piece to show our transmission packages," Atkins says. Grubb Worm became not only a race car, but a promotional vehicle for Tick Performance.

A new turbo kit was fabricated, but the LT1 stock engine block remained. The car became successively quicker with this setup over the next couple of years, reaching high-6-second ETs. Atkins says he's never been tempted to switch to a simpler, easier-to-tune automatic transmission.

When drag racing became popular after WWII, the cars in those races had conventional manual transmissions, forcing you to row through the gears yourself. Drag racing's premier sanctioning body, the National Hot Rod Association (NHRA), first formally accepted cars with automatic transmissions in 1960. While H-pattern manuals remained the standard in big-time drag racing through the 1960s, torque-converter automatic transmissions overtook them in popularity by the 1970s and 1980s.

At that time, the quickest remaining manuals were running low-10-second quarter-mile elapsed times (ETs). A dwindling number of manual cars were raced professionally and in grass-roots drag racing during the 1980s, 1990s, and early 2000s, but they were seen as oddballs—fragile and relatively slow. By 2010, interest in stick-shift drag racing slowly resurfaced.

Racers began to see shifting gears, themselves, as a challenge. Movies like The Fast and the Furious stirred interest in illicit street racing, wherein manual-transmission muscle and import cars remained prevalent. That, in turn, began to influence track racing, and a few racers made waves with stick-shift cars that could run mid-9-second passes. But interest really began to pick up around 2017 and 2018, Atkins says, when regional stick-shift racers like Wesley Evans and Yandro created excitement and awe by posting low-8-second and high-7-second quarter-mile passes in "Fox-Body" Ford Mustangs.

Atkins also points to YouTuber Cleetus McFarland, whose millions of viewers cheered when he set the GM stick-shift record in 2018, ripping off a 7.82-second pass in his skeletonized Corvette, "Leroy." McFarland raced with Atkins and others in the stick-shift class at last year's World Cup, as well. He tells Popular Mechanics that the unpredictability and drama of stick-shift drag racing are what appeal to him.

"The No. 1-qualifier can be taken out by the last-place qualifier," McFarland says. "So much can go wrong on one pass. It's definitely better content for YouTube." Fellow YouTuber and stick-shift-class racer, Sean Madden, agrees. "There's a lot more to think about when you’re in the cockpit of the car. There's more room for error [when shifting gears], which translates into more of a driver's race than a car race," he tells Popular Mechanics.

The drivers take heart and energy from the fans, who love to see the manual trans cars run, Atkins says. "It's fun to watch, and a lot of people can relate, because they may have a manual-transmission street car."

That enthusiasm drove Haltech World Cup Finals organizers, Chris and Jason Miller, to formally include a stick-shift class for the first time in the history of the 25-year-old event in 2021. Twenty cars showed up. This past year, 25 cars entered the class. Like Atkins’ Grubb Worm, the fastest have one key thing in common: an adjustable clutch.

The adjustable clutch, sometimes called a "slipper clutch," is not new in drag racing. Its origins go back to the 1960s. It's essentially a high-performance variation on the clutches we’ve run in manual-transmission street cars for over 90 years.

In very basic terms, a standard single-disc manual transmission clutch assembly is a bit like a layer cake. When the layers are squeezed together, they transmit torque from the engine to the gearbox and ultimately to the drive wheels. (To understand how it works, watch a couple of animations.)

A key thing to recognize is that there is always some slip as the clutch disc and flywheel come together, before they fully grip and essentially lock. A driver controls this slip by modulating the clutch pedal—releasing it slowly from a fully depressed, disengaged position to the point where it "bites," or engages. Drivers develop a feel for the bite point and how quickly and smoothly they can modulate the clutch pedal.

An adjustable clutch capitalizes on this "slip." It has counterweights, which control the rate at which the clutch engages, allowing a driver to basically sidestep the clutch without it immediately locking up and stalling the engine. "The clutch takes care of all that," Atkins says. "It kinda makes it look like I don't need to be a good driver."

Racers tune slipper clutches for track conditions (grip) by adding or subtracting weight from levers that force the pressure plate against the clutch disc—extending or abbreviating clutch slip and lock-up as engine RPM rises.

"That's what allows us to make 2,000 horsepower," Atkins adds. "When we leave the starting line it gives us that initial slip. We leave with 900 hp, but as the RPM and power increase down-track, that clamp load increases to the point that the clutch is transmitting that 2,000 hp."

When Atkins creeps up to the starting line, he presses the clutch pedal to the floor. He lightly pumps the brake pedal to set the line-lock switch (allowing the front brakes to lock independently of the rear brakes). He raises the engine to between 5,000 and 5,500 RPM and waits for the tree to count down.

✅ What Is Quick?For those unfamiliar with drag racing, it's worth delineating the hierarchy of quick times and speeds. Nitro-methane-burning Top Fuel dragsters are the top dogs—the quickest, fastest drag racing cars on the planet. Using a high-tech six-disc centrifugal clutch instead of a familiar automatic or manual transmission, they cover 1,000 feet from a dead stop in as little as 3.6 seconds at 338 mph. The quickest nitro-burning Funny Cars (which also use centrifugal clutches) are a tick behind at around 3.8 seconds and 333 mph. Pro Stock cars cover 1,000 feet in about 6.5 seconds at 210 mph. A variety of other quarter-mile automatic transmission classes from Pro Mods to Top Sportsman cover 1,320 feet in as little as 5.7 seconds to just over 8 seconds. And the quickest factory stock street cars? They run the quarter in the 10- to mid-10-second range. Despite its manual transmission, Grubb Worm's 6.61-second ET puts it in rarefied territory with the fastest non-nitro drag racing cars in the world.

"When I dump the clutch, the RPM will actually flash up to 6,500," he says. The slipper clutch is still slipping. As the car accelerates and the engine revs up to around 9,200 RPM, the clutch locks up. Then, it's time to upshift from first to second gear. Atkins is already anticipating the next shift. In fact, he puts back pressure or forward pressure on the gearshift lever throughout the pass. When the engine reaches its pre-set rev limit (over 9,000 RPM), he shifts from second to third, from third to fourth.

Unlike street-car drivers, he doesn't use the clutch after launch. At the defined rev limit, an ECU cuts ignition (and thus torque) during the tenth of a second it takes Atkins to shift. Ignition then resumes in the next gear, and the slipper clutch progressively locks up as the engine races to 9,000-plus RPM. Fans hear the ignition cut and resumption, which makes a concussive noise. Since fuel delivery is not interrupted, unburned fuel ignites, shooting flames out of the 5-inch exhaust forward of the Camaro's right front wheel. You might call it functional theater.

"What I’m doing is so simple," Aktins says. "I’m basically shifting as I run into the rev limiter. Once it hits the limiter, it just bangs into the next gear. I don't have to watch the tachometer." The rev limiter has a 1,500 RPM spread rather than the typical streetcar 50 RPM spread, giving him enough time to move the lever before engine RPM drops. Atkins’ modesty belies the fact that all of the above happens during a portion of the sub-7-second run. In fact, Atkins did miss a shift at WCF and at the previous race.

In early 2022, Atkins was finally persuaded to switch to an aftermarket "Bow-Tie" engine block, paired with a single 102-millimeter turbocharger, after wear on the LT1 became an issue.

"The engine makes basically seven times as much power as stock. The car probably does 0 to 100 mph in less than 2 seconds now. With the gearing, it will run about 85 mph in first gear at 9300 RPM, which comes at just over 1 second!"

At the World Cup Finals last year, the team hoped to beat the world record it had just set in Florida, possibly running as quick as the 6.40s, though they were a bit unsure. "We just don't have a lot of experience with the Chevy Bow-Tie block that's now in it," Atkins says. In the end, a mysterious fuel/backfire issue, possibly wiring-related, thwarted them.

It popped up a couple of times during the World Cup Finals, the last when Atkins staged for the semi-final race. "As soon as it got [launch boost], it fuel-flooded, or choked itself, and just stalled," he says. Despite the disappointment, Atkins is planning a full race schedule in 2023.

"World Cup is survival," he reflects. "Five rounds of qualifying, and then you have to make it to the end of the race. We had the car to beat. We just had issues."

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