Looking Back At The Famous Duntov Small-Block Chevrolet Camshaft

In the early to mid-fifties, horsepower wars were just getting fired up, and aspiring racers and engineers were burning the midnight oil trying to figure out a way to get an upper hand against the cross-town competition. For Chevrolet, their ace in the hole was a Belgian-born American engineer named Zora Arkus-Duntov. His passion (and some of his antics) are legendary around the halls of General Motors, and often, his passion for performance wasn’t shared with the upper brass at GM or Chevrolet.

Duntov

Zora Arkus-Duntov was a car guy’s car guy. As Chevrolet’s Director of High Performance, he looked for power throughout the entire engine. The Duntov cam bears his name at Chevy, same as the ARDUN heads do for early Fords. (Used with permission, GM Media Archives)

Undeniably a hot rodder at heart, Zora rose among the ranks about as quickly as Chevrolet’s cars pulled away from the rest of the pack. Zora was soon promoted to Chevrolet’s Director of High Performance in 1957, and was given Corvette’s official Chief Engineer title ten years later. Fittingly, one of the most revered performance camshafts from this era still bears his name.

Duntov

It’s amazing to think the technology that this old, flat-tappet cam delivered back in the day.

The initial design of the small-block Chevy engine was birthed in the desire for higher power in a more compact, lightweight package. When the 265ci small-block appeared in 1955, it suited those demands fairly well. But, engineers were not resting on their laurels, as high-lift cams were introduced almost immediately to capitalize on the free-flowing characteristics – relatively speaking – of the new engine. The 1956 parts manual saw the introduction of a new, high-lift, performance camshaft, part number 3734077, which was available in the ’56 Corvette’s 240hp, 265ci V8.

…you can appreciate the Duntov cam, as well as that entire engine, for the amazing achievement it was in its day. – Billy Godbold, Comp Cams

For 1957, the small-block engine’s rear-most cam bearing journal was modified for better lubrication, and the groove on the camshaft’s rear surface was no longer necessary. Another new cam featured the same duration as the previous year’s (077) high-lift version at 287 degrees, but lobe lift was reduced slightly. The cam’s new part number ended with the more widely-known “097”, aka, the “Duntov” cam. This cam was used by Chevy in all solid-lifter applications from ’57 through 1963. This included all the 270, 283, 290 and 315-horsepowered 283s and the later 327 engines with 340 and 360 horsepower. While the Duntov cam was quite radical and considered a racing-spec camshaft that would still meet SCCA Showroom Stock rules, its performance was also supported by the small ports and intakes used on the 283 and 327 engines.

Duntov

Duntov surrounded himself with performance, and performance-minded people. This made him a prime target for those within GM that didn’t share his enthusiasm for speed. (Used with permission, GM Media Archives)

The “Duntov Cam”, aptly named after the budding engineer that spearheaded much of Chevrolet’s performance efforts through the ’50s and for two decades afterward, was actually known within GM as part number 3736097. Many times, it would simply be referred to by Zora’s last name, or as the “097 cam” over many GM parts counters for expediency’s sake. Keeping in mind that the performance-minded, solid-lifter cam was introduced only two years after the small-block Chevrolet engine began production, it’s easy to see Zora’s influence in laying an early foundation of the small-block Chevy’s dominating force in performance.

Beyond “097”

As engine size and horsepower was steadily increasing in 1964, Chevrolet replaced the Duntov cam with a newer version, dubbed the “30-30” camshaft to achieve 365 and 375 horsepower from the 327. This was a replacement and is not an iteration of the Duntov cam, although some have joined the two monikers and refer to it as a “Duntov 30-30”.

Duntov

Zora shares the new for ’57 fuel-injection with the press. Early fuelie engines used the Duntov cam until 1964 production, where it was replaced in the highest horsepower 327 engines. (Used with permission, GM Media Archives)

Where the Duntov cam was engineered to meet SCCA Showroom Stock requirements, the 30-30 camshaft was a full-on racing camshaft. These cams took on mythical proportions because they were cheap and available at every Chevy dealer. The Duntov cam worked great with the 283’s smaller ports and valves, but as the higher horsepowered 327s came along, the “racing cam” with the famous name was found wanting for more. In response, Chevrolet created the 30-30 cam and sought to give racers the most performance for their better breathing and higher-winding 327s.

The term 30-30 is a reference to the solid-lifter cam’s valve lash settings assigned by Chevrolet. While the 30-30 cam does use recommended lash settings upward of .030-inch for both intake and exhaust, the Duntov camshaft uses a much tighter recommended lash of 0.012-inch and 0.018-inch for intake and exhaust. The 30-30 cam is a solid lifter performance camshaft, but is an entirely different camshaft altogether from the “097” Duntov cam.

The Duntov cam was one of the first high-lift cams designed for the small-block Chevy engine. As performance needs grew, so did overlap and lobe lift. Mushroom lifters used their larger base diameter for yet more agressive cams and the Edge-Orifice lifters reduced oil flow to the requisite roller rockers to control oil starvation at high rpm. Piddle-Valve lifters are solid lifters and were used in production engines. All Chevrolet camshafts were designed to use factory springs and rocker arms which had an effective ratio of 1.37:1.

The focus on racing meant that the 30-30 cam was not a street friendly camshaft by anyone’s imagination. It makes great power above 4,000 rpm, but the cam leaves a lot of torque on the table below that RPM. Not to say that street driving isn’t doable with the 30-30 cam, but if installed in a heavy, auto-equipped car with highway gearing, the result will be far less than satisfactory. Trim the weight, learn to shift, and put in some 4:00 or higher rear gears, and the 30-30 cam can be a hoot to drive, and its lope at idle will make enthusiasts green with envy.

Designed for showroom stock racing, the Duntov cam worked well in the new fuel-injection designed for racing back in 1957, and in production engines in 1963.

As a stop-gap between the Duntov and 30-30 cams, and to better suit larger 350ci engines, Chevrolet released the “LT1” cam in 1970, which carried part number 3972178. Used in the 1970 (second-sen) Camaro Z/28 and the ’70-’72 Corvette LT1, it is considered the final chapter in the development of Chevrolet factory solid-lifter cams. It has very similar idle vacuum characteristics and idle quality as the original Duntov, but unlike the 30-30 cam, it had a broad torque range coupled with excellent top-end power. The solid-lifter LT1 cam makes about 20-percent more low-end torque than the 30-30, gives up very little above 6,000 rpm, and like both the Duntov and 30-30 cam, it is designed to work with the bulletproof, stock valvetrain. In fact, it’s still available in kit form from Chevrolet Performance under part number 12364054.

Lashing Out

The Duntov cam, as well as the others discussed in this story are all mechanical cams using solid lifters. As with any solid-lifter camshaft, there needs to be a certain amount of operating clearance or lash set into the valvetrain to ensure long life and proper performance. One of the endeared characteristics of mechanical cams is that signature tapping of the valvetrain. Once heralded as an indication of performance, that tapping indicator of lash under the valve covers still endears itself to many enthusiasts.

But what is lash, and why does one camshaft require more of it than another? Just like setting the ignition timing, valve lash has certain recommendations from a camshaft’s manufacturer, but ultimately, it comes down to the particular application and expectations of the end user. This is due to many reasons.

Cam lobe design has moved beyond simply lift and duration. The Duntov cam was a predecessor to many of these designs.

When running any solid-lifter camshaft, there needs to be a certain amount of clearance built into the system. This allows for expansion of the metal parts as the engine reaches operating temperature. If all the components expand at the same rate, lash would be less of a consideration, but that is not the case. As various components within the engine heat up independently, they expand at different rates. Aluminum heads will increase this expansion, and when you have an aluminum block also, the growth is even more dramatic.

Fuel injection design changed in ’63 and in ’64 the 30-30 cam was used for the highest-horsepower engines.

Comp Cams’ Billy Godbold explains it best, “When the engine first cranks, the exhaust valve is typically the first valve train component to significantly change temperature. As it heats, the metal expands increasing the length, and the exhaust lash clearance would tighten slightly… If there was zero lash, this would result in the exhaust valve hanging open during combustion, and the flow of hot pressurized exhaust gasses around the seat would quickly destroy that exhaust seat.” When you consider how much variation there could be until every component equalizes to operating temperature, it’s easy to see how having a little slack between components will help make up for different expansion rates.

But what about cold, hot and running lash? Adjusting lash cold is simply that, measuring the amount of clearance with all components at room temperature. Hot lash is what you measure in a hot engine as soon as you stop the engine and get under the valve covers to measure the lash. Running lash is the amount of clearance the valvetrain actually sees in operation with the temperatures equalized.

The 30-30 cam was designed for the cross-ram 302 in the Camaro Z/28, which still used cast manifolds in stock form. This high-winding cam was designed for tall gears and high rpm.

Some prefer a slightly tighter lash setting, which will increase lift slightly. It will also increase duration, which may have adverse effects on idle vacuum. Some will opt for more lash while still staying within a reasonable range of recommended specs. Keen readers will likely note that the Duntov and LT1 cams’ lash is much tighter than the 30-30 cam’s rated lash setting. Without oversimplifying, the design of the camshaft and its lobes dictated the difference.

Billy Godbold breaks down the cam’s special setting, “What people don’t know, is the designed hot lash was supposed to be more like .020-.024-inch. GM did not want to run tighter than those values because they knew the seats could erode over time (even with leaded fuel), and that they needed more than .005-inch “cold” at the end of any service interval so the engine would start under even colder conditions. The reason it became the 30-30 cam is because it ran so much better with the lash opened up to .030-inch hot. At this looser lash setting, the system was accelerating though the lash take-up, thereby keeping everything in compression. The quicker action also worked great to minimize seat timing without dramatically reducing area under the curve. This allowed the engine to respond more quickly to throttle inputs while improving low-end torque.”

Decoding Cam Numbers

You also may see camshafts referenced with the last few final numbers different from the cam’s official GM part number. For instance, the Duntov cam has a GM part number 3736097 but cast into the camshaft is the number 3736098. It doesn’t indicate a different cam or an earlier or later version. That number is actually the casting number of the camshaft, not the part number. Retired GM employee, John Hinckley, an NCRS Master Judge, explains the one number difference, “Each Chevy camshaft had its own dedicated casting number to minimize the cam-grinding cycle time. When you consider that Flint V8 ground 5,500 cams every day, you can see how important it was to keep track of what you were grinding.”

Does Anyone Still “Do” A Duntov cam?

With larger engine sizes and better breathing components, is there still a case to grind cams with that Duntov design? The answer is a resounding yes, but you need to know why it makes sense. For obvious reasons, the number of 283 and 327 engines that left Chevrolet’s engine plants with this camshaft means that it’s still the obvious choice for a proper restoration or someone looking to recreate that vintage sound. The Duntov cam’s increased drivability over other solid-lifter options means that those searching to relive their youth in a vintage Corvette could still enjoy street-friendly gearing and automatic transmissions without adverse accommodations. Conversely, there will always be the LT1 and even wilder 30-30 camshafts for those where this is not an issue.

While big-block Corvettes are iconic, Zora preferred high-winding small-blocks with performance cams.

We spoke with Godbold, the brain behind many of Comp Cams’ designs, about the Duntov camshaft and how it fits into today’s spectrum of engine designs. He was quick to point out, “When you step back and realize how much progress had been made in the first 50 years of American engine development, you can appreciate the Duntov cam, as well as that entire engine, as the amazing achievement it was for its day. But, other than the fact that a modern SBC camshaft looks kind of similar and has many of the same overall dimensions, almost nothing is left over from those 50+ year old designs.”

“That said, I cannot think of a good reason to run a Duntov camshaft in any non-restoration package, as you are immediately giving up more than 50hp due to the lazy valve events and low area under the curve.” While the Duntov cam is/was considered to be a performance cam, there is good reason why we might not want to consider it the end-all for performance. The camshaft was tailored for SCCA showroom stock racing, which meant that factory exhaust manifolds and intakes were used in these applications. Billy does explain that a better flowing set of heads, exhaust, and intake does benefit performance pretty much across the board, but you are limited how far you can go before the engine is no longer a restoration project, and therefore, a higher-performing, modern camshaft with a broader operating range should be available.

Aftermarket Alternatives

That doesn’t mean that you’ll have to give up that signature sound at idle. In fact, the opposite is true. Many manufacturers have begun reproducing these vintage camshafts, and in many instances, they have infused modern technologies to better suit the end user. Billy explains, “There is a Comp Cams series of cams called the “Nostalgia Plus” series that match the opening and closing ramp rates and valve timing events of the original cams. They also have the option of either hydraulic or solid tappets and more area under the curve for more power. The hydraulic mimic cam of the 30-30 is Comp part number 12-672-4.”

For those wanting to relive that same vintage soundtrack at idle, you could use the Nostalgia Plus in either solid or hydraulic or the Thumpr series for a bit more sound at idle. Today you even have the option of converting over to a hydraulic or solid roller valvetrain. The venerable SBC platform can be brought up to almost any performance target you can imagine with the amazing aftermarket support available today.

Cam Idle Comparison

Duntov

30-30

LT1

Are those vintage grinds relegated to the history books forever? Heaven forbid! It just means that while many will look back at that early era of performance as a simpler time, the rules of physics were still just as much at play, they’re simply much better understood today. Understanding what they are, and why they worked back then will help you to capture all the mystique and nostalgia that these early grinds can provide. If you require more, like improved fuel mileage, highway gears and drivability, you may want to divert your view to a more modern design. Either way, having a clear, realistic view of your goal will help you get the most out of any camshaft you decide.

Article Sources

About the author

Andy Bolig

Andy has been intrigued by mechanical things all of his life and enjoys tinkering with cars of all makes and ages. Finding value in style points, he can appreciate cars of all power and performance levels. Andy is an avid railfan and gets his “high” by flying radio-controlled model airplanes when time permits. He keeps his feet firmly grounded by working on his two street rods and his supercharged C4 Corvette. Whether planes, trains, motorcycles, or automobiles, Andy has immersed himself in a world driven by internal combustion.
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