In the early years of Pro Stock racing, weight-to-power ratio was the key to success. Unlike today’s modern drag racing builds, where advanced computer simulations and high-tech materials dominate, Bill “Grumpy” Jenkins relied on raw mechanical ingenuity and a deep understanding of engine physics to beat his competition.
His weapon of choice? A 331 cubic-inch small-block Chevy, a powerplant that defied conventional wisdom and dominated the Pro Stock circuit. Jenkins’ engineering brilliance turned his Vega into an unstoppable force, winning him so many races that he became the highest-paid athlete of the year—a feat unheard of in motorsports at the time.
But what made Jenkins’ 331ci Chevy so revolutionary? Let’s dive deep into the build, the strategy, and the legacy of one of the greatest drag racing engines ever created.
The Perfect Pro Stock Engine: Power vs. Weight
Why Smaller Was Better
In early Pro Stock racing, weight regulations dictated that smaller engines could be placed in lighter cars, making them more competitive. Instead of opting for a massive big-block engine, which most racers believed was the best way to win, Jenkins saw an opportunity to maximize performance while staying within the rules.
He realized that a lighter, high-revving small-block engine could out-launch heavier big-block-powered cars, giving him an edge over the quarter-mile. His goal was simple: maximize horsepower while keeping weight to a minimum.
Building the 331ci Small-Block Chevy
Jenkins’ engine build was a masterclass in precision tuning and performance optimization. His 331ci setup featured a combination of carefully selected components that worked in perfect harmony:
- Block Selection: He used a Chevy 350 4-bolt main block, known for its strength and reliability, providing a solid foundation for high-RPM operation.
- Crankshaft Choice: Instead of using a standard 350 crankshaft, he installed a small journal 327 crankshaft with bearing spacers. This shorter stroke design allowed the engine to rev higher, making it perfect for drag racing.
- Bore & Stroke Optimization: He bored the cylinders .030 inches over, increasing displacement slightly while maintaining reliability and durability.
- Rod Length Adjustment: Jenkins chose 5.85-inch connecting rods, slightly longer than stock 5.70-inch rods. This improved the rod-to-stroke ratio, reduced piston side loading, and allowed for smoother high-RPM operation.
- Cylinder Heads & Valvetrain: Jenkins used high-flowing cylinder heads with precision-tuned valvetrain geometry, ensuring optimal airflow and combustion efficiency.
- Fuel & Ignition System: He fine-tuned carburetor jetting, ignition timing, and valve lift, creating a highly responsive engine that produced maximum power throughout the RPM range.
By fine-tuning every aspect of the engine, suspension, and weight distribution, Jenkins was able to outperform larger displacement engines that were theoretically more powerful but struggled with excess weight.
The Vega That Dominated Pro Stock Racing
When Bill Jenkins installed his 331ci small-block Chevy into his Chevrolet Vega, he set the drag racing world on fire.
A Streak of Victories
- His Vega was unbeatable, dominating the NHRA Pro Stock class.
- He won race after race, proving that a lightweight, high-revving small-block could outclass larger engines.
- His success was so overwhelming that it forced other racers to rethink their engine-building strategies.
Jenkins’ Vega quickly became one of the most feared Pro Stock cars ever built. His revolutionary approach to engine tuning and weight reduction changed the way Pro Stock racers built cars for years to come.
The Engineering Genius Behind Jenkins’ Success
Bill Jenkins’ dominance in Pro Stock racing was no accident. His understanding of mechanical physics, aerodynamics, and power-to-weight efficiency was far ahead of his time.
1. Understanding Weight Transfer & Traction
Most racers focused on raw horsepower, but Jenkins understood that getting that power to the ground was just as important. He optimized his suspension setup and chassis balance to maximize traction, allowing his Vega to launch harder and faster than the competition.
2. Mastering High-RPM Performance
The 331ci small-block Chevy was a high-revving beast. While big-block engines struggled with heavy rotating mass, Jenkins’ lighter reciprocating components allowed his engine to scream to higher RPMs, delivering peak power where it mattered most.
3. Smart Engine Tuning
Jenkins was a master of carburetor tuning, ignition timing, and camshaft selection. His ability to fine-tune every aspect of his engine’s operation gave him an edge that many competitors couldn’t match.
4. Pioneering Lightweight Pro Stock Builds
Before Jenkins, most Pro Stock racers relied on brute force to win races. Jenkins proved that weight reduction and intelligent engineering could be just as effective, inspiring future generations of racers to prioritize aerodynamics, power-to-weight ratio, and mechanical efficiency.
How Jenkins Became the Highest-Paid Athlete
Bill Jenkins’ revolutionary Vega and 331ci small-block Chevy didn’t just make him famous—they made him rich.
- With every win, his reputation grew, making him one of the most sought-after engine builders in the industry.
- His race winnings, sponsorship deals, and consulting work helped him become one of the highest-paid athletes in any sport at the time.
- His success set a new standard for drag racers, showing that smart engineering and innovation could be more valuable than raw power alone.
Legacy: How Jenkins’ Engine Changed Racing Forever
Even though drag racing technology has evolved significantly since Jenkins’ time, his impact on the sport is still felt today. His innovative approach to engine building, weight management, and high-RPM efficiency inspired countless racers and mechanics.
What Jenkins’ 331ci Small-Block Taught Future Generations:
- Bigger isn’t always better—sometimes a smaller, well-tuned engine can outperform larger displacement builds.
- Weight reduction is just as important as horsepower—a lighter car with less power can still win against a heavier, more powerful car.
- Engineering knowledge beats big budgets—Jenkins didn’t need the most expensive parts to win; he needed the smartest strategy.
Today, engine builders still study Jenkins’ techniques, applying his high-revving small-block philosophy to modern racing engines.
I built and ran a very similar engine and ran it in a somewhat lightened 66 Chevelle SS body. My base was a 67 327 small journal two bolt main block. It was balanced and blueprints to the max. I ran 11.5 compression forged pistons with moly rings in a 40 over build making 336 cubic inches. I ran the 2″ valve heads with Harland and Sharpe roller rockers and pushrod guides with screw in studs. Edelbrock C3BX intake with a Ford Holley 715 CFM converted to manuel secondaries and secondary squirters.. Mallory distributor and Doug Thorly headers. I could turn over 9 grand anytime I needed in order to get a better next gear. Rock Crusher 4 speed and 4:56 gears. With a vertical gate shifter. I could pick the front tires off the ground in second.
This combination was fantastic on the strip or street and the only maintenance was an oil change one weekend and sparkplugs the next.
Need a book,”Bill Jenkin’s secrets of speed”. What did he use for a cam and pistons?