PRI Magazine January 2014 : Page 58
By John F. Katz faster-turning engines—hungry for more air—continue to drive development of new cylinder heads for drag racing. “The drag racing market continues to push the envelope on larger-cubic-inch applica-tions,” observed Kevin Feeney of Racing Head Service (RHS), Memphis, Tennessee, “increasing the demands on cylinder heads. Raised intake ports, with larger-cross-section runners and flatter valve angles, continue to be the trend.” “Everybody wants to go bigger,” agreed Jason Neugent of BIGGER, Brodix, Mena, Arkansas. “It doesn’t seem that long ago that a 502 was considered large; now an engine has to be over 700 cid to be ‘big.’ So you have to have cylinder heads that fit those cubic inches with bigger port volumes providing more airflow.” Of course, there’s more to cylinder head engineering than just increasing airflow. Air velocity matters, as do myriad other factors. Additionally, advances in Computer Aided Manufacturing (CAM) continue to enable more precise and consistent machin-ing. Computer modeling, including Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA), are now commonplace at the OE level; although the degree of their influ-ence on racing heads remains somewhat debatable. What’s Happening Where For now it’s worth noting that the better-financed professional classes are pushing the frontiers of cylinder head development. “The pro and outlaw classes have no rules and no limits,” noted Carroll Carter of C & C Motorsports, Manassas, Virginia. “So innovation and experimentation with different combinations is popular. The search for the perfect port design and flow fea-tures now involve not only the cylinder head itself but cylinder-head-and-manifold combinations, and how they contribute to the total engine package.” C & C manufactures bare castings for Ford big block hemi-style applications, with 4.9-and 5.0-inch bore spaces. “And we’ve had inquiries relative to even bigger horsepower applications,” Carter added; so C & C plans to release a casting for a 5.3-inch bore space as well. “In the professional ranks,” Feeney agreed, “the Pro Stock division continues to be the most aggressive in cylinder head development”—while at the same time, new technologies are migrating down to the sportsman ranks even faster. Sonny Leonard of Sonny’s Racing Engines and Components, Lynchburg, Virginia, reported that the biggest advances are being made in “valvetrain geometry and combustion chamber shape, enabling ultra-high rpm in the professional categories.” “In classes where the rules determine valve size and place-ment, the advances have been small,” added Rick Wilkinson of Alan Johnson Performance Engineering (AJPE), Santa Maria, California. “But where the valvetrain permits an engine to increase rpm, cylinder-head port cross sections and flow rates must increase to keep up with the new demand.” “There have been advances based on valve angle, both inclined and canted,” said Dick Maskin of Dart Heads, Troy, Michigan, “as well as in short-turn height, the height of open-ings, and both intake and exhaust location. Most important 58 Performance Racing Industry | January 2014
Drag Race Cylinder Heads Designed To Dominate
John F. Katz
Bigger, faster-turning engines—hungry for more air—continue to drive development of new cylinder heads for drag racing. “The drag racing market continues to push the envelope on larger-cubic-inch applications,” observed Kevin Feeney of Racing Head Service (RHS), Memphis, Tennessee, “increasing the demands on cylinder heads. Raised intake ports, with larger-cross-section runners and flatter valve angles, continue to be the trend.”
“Everybody wants to go bigger,” agreed Jason Neugent of Brodix, Mena, Arkansas. “It doesn’t seem that long ago that a 502 was considered large; now an engine has to be over 700 cid to be ‘big.’ So you have to have cylinder heads that fit those cubic inches with bigger port volumes providing more airflow.”
Of course, there’s more to cylinder head engineering than just increasing airflow. Air velocity matters, as do myriad other factors. Additionally, advances in Computer Aided Manufacturing (CAM) continue to enable more precise and consistent machining. Computer modeling, including Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA), are now commonplace at the OE level; although the degree of their influence on racing heads remains somewhat debatable.
What’s Happening Where
For now it’s worth noting that the better-financed professional classes are pushing the frontiers of cylinder head development. “The pro and outlaw classes have no rules and no limits,” noted Carroll Carter of C & C Motorsports, Manassas, Virginia. “So innovation and experimentation with different combinations is popular. The search for the perfect port design and flow features now involve not only the cylinder head itself but cylinderhead head- and-manifold combinations, and how they contribute to the total engine package.” C & C manufactures bare castings for Ford big block hemi-style applications, with 4.9- and 5.0-inch bore spaces. “And we’ve had inquiries relative to even bigger horsepower applications,” Carter added; so C & C plans to release a casting for a 5.3-inch bore space as well.
“In the professional ranks,” Feeney agreed, “the Pro Stock division continues to be the most aggressive in cylinder head development”—while at the same time, new technologies are migrating down to the sportsman ranks even faster.
Sonny Leonard of Sonny’s Racing Engines and Components, Lynchburg, Virginia, reported that the biggest advances are being made in “valvetrain geometry and combustion chamber shape, enabling ultra-high rpm in the professional categories.”
“In classes where the rules determine valve size and placement, the advances have been small,” added Rick Wilkinson of Alan Johnson Performance Engineering (AJPE), Santa Maria, California. “But where the valvetrain permits an engine to increase rpm, cylinder-head port cross sections and flow rates must increase to keep up with the new demand.”
“There have been advances based on valve angle, both inclined and canted,” said Dick Maskin of Dart Heads, Troy, Michigan, “as well as in short-turn height, the height of openings, and both intake and exhaust location. Most important Are what you see—line of sight—looking straight into the port as far as the seat area; and the cross-section of the port. Airflow is a distant third, as it is the simplest to achieve.”
Matt Bieneman of MBE, Mooresville, North Carolina, noted how “our Top Fuel head has set a national record, and it’s been winning championships. One team, which had been qualifying 9th or 10th in every race, put them on and went straight to the pole. And because of our success with that Top Fuel head we decided to release a blown alcohol head, which we also offer with the NHRA-regulation 2.400-inch intake valve for pro modified. And we’ve seen great results.”
MBE has also “built our own conventional-style big block Chevy head. What makes that head inherently inefficient (as it comes from the factory) is that you can’t get enough area over the short turn without expanding the width of the port. The air has to turn through almost a 90-degree angle. But we raised the spring pocket on the intake side .500 inch, and that created a huge radius in the roof, so the flow numbers go up as much as 10–13 percent at every lift over .300. Thirteen percent may not sound like much, but that’s 40 cfm in some places—and that’s a big gain,” said Bieneman.
Another problem with “the way it was originally designed” is that there are ‘good’ ports and ‘bad’ ports, and in the ‘bad’ ports “the air pressure is lower along the intake wall that’s next to the exhaust, away from the cylinder,” he continued. “We could never get the air to stay connected to that wall, and that’s why flow numbers were always down 10–15 percent for those ports. It didn’t matter who did the porting. We tried putting fins in there; we tried all kinds of crazy things. But since we raised the valve pocket, the air stays attached on that common wall—and that’s why the power gains have been so large.”
Neugent also noted recent advances in oval-port, big block Chevy heads. “The airflow is greater, the air speeds are faster,” he said. “We learned that there was a lot of dead space in the rectangular port configurations. So we started putting more radius in the corners and following that all the way through the ports. And it really improved the airflow numbers.”
New from Brodix is the SR-20: “It looks more like a conventional big block head,” Neugent continued, “but the intake ports are raised .500 inch. And we’ve extended the ports to increase port volume to 440cc, which is bigger than some of the Big Duke heads. It has a 20-degree valve angle, real small 95cc chambers, and it flows 515 cfm. So it’s a conventional-style head that can feed a decent-size engine. And it also works real well on smaller engines, too, such as a 588, where we saw a larger horsepower increase than on a 632.
“We also have a new LS7-based head we call the BR7, and we have some new options for that,” he added. “We have one that will accept a bigger spring pocket. In the stock casting, if you try to cut the pockets to fit bigger springs you usually break through somewhere. So we beefed them up so you can fit 1.550 springs or larger. Now if you want to run a larger cam, your valve springs won’t be an issue.” Additionally, Brodix has “an LS3- based cylinder head in the works.”
“We see a trend back toward conventional-style heads,” confirmed Mike Weinle of Weinle Motorsports, Cleves, Ohio. “The industry has come out with conventional heads that are so much better; you can get almost 1200 horsepower out of them. And, of course, they cost $2000 to $5000 less, and more standard parts fit them. So people are moving away from the Big Chief-style heads and going back to the conventional style.” This trend has been influenced, Weinle continued, by the growing percentage of drag strips that run only one-eighth mile, where a conventional head is only two or three hundredths slower than a Big Chief, he noted.
Weinle recently invested in a CNC machine, enabling the company to produce “our own CNC versions of popular heads.” The company offers its own versions of the Pro-Filer 380X, which is based on the Pro-Filer 375X, and its Pro-Filer 12 Hitman heads that are CNC ported, along with its 385X, which is based on the Brodix Head Hunter 380 and 383 oval port heads.
Scott Patton of M&M Competition Engines, Indianapolis, Indiana, also noted the recent trend toward “increased performance from more ‘conventional’ big block heads. In many heads-up, streetcar classes, cylinder heads are restricted to a conventional design. This has led to power levels from well-designed conventional castings that used to be reserved for raised-runner or spread-port heads.”
Our experts spotted other trends as well. “We’ve seen a lot more heads designed as complete packages,” said Mike Schropp of Livernois Motorsports, Dearborn Heights, Michigan. “There has always been a market for complete heads, but it seems like we’re seeing more heads that are fully outfitted in complete form, and with options as well to make the head best fit the application where it is going to be used.”
“Advancements in the valvetrain also continue,” added Feeney. “More robust rocker arms, pushrods and lifters have provided the ability to increase valve lift and rpm, even on larger-displacement engines.” Such changes influence not only airflow, but “packaging,” which must “ensure adequate clearance for larger pushrods, and provide for taller installed spring heights.”
“Direct injection is the technology to keep an eye on,” said Tony Mamo of AFR (Air Flow Research), Valencia, California. “It’s becoming more popular in OE applications, and will likely be making its way up the ranks in the racing world over the next few years.”
It seemed logical at this point to ask how much of this advanced technology is driven by—or at least facilitated by—corresponding advances in computer modeling. We received varying, even conflicting answers.
“The advances have been exponential in the design of Formula 1, IndyCar, NASCAR, and Pro Stock cylinder heads,” replied Chris Frank of Frankenstein Racing Heads, Joshua, Texas. “The software allows engineers to see the parts of the port where good air quality is saturated.” Drag racing classes using power adders have benefited particularly, including “X275, Outlaw Drag Radial and Pro Mod.”
Computer modeling has also opened “limitless options for machining billet heads,” added Patton, “and as a company, M&M has taken full advantage of this.” Power adders are very popular in drag racing, and advances in that technology have increased the stress on cylinder heads. “Billet cylinder heads are seen more often as castings and are reaching their limits with extreme power adders. With the aid of computer modeling we can produce billet cylinder heads quickly and efficiently, enabling us to offer the racer a billet head at a cast price.”
“Computer modeling is almost a necessity in designing modern cylinder heads,” said Leonard. “A 3D solid modeling package allows the designer to properly lay out and analyze valve placement and port design, and to note rocker geometry prior to manufacturing. FEA allows the designer to analyze the stresses that the cylinder head and related components are subjected to during operation. Being able to visualize and quantify stresses and displacements allows the designer to improve part durability and performance prior to manufacture, which can greatly reduce product development costs.”
CFD, on the other hand, “is a very powerful tool,” Leonard added, “but it tends to be cost-prohibitive for most engine builders, especially those who cater to racing without large corporate sponsorships. When you consider the upfront cost of the software, coupled with the engineering and computer resources required for its operation, it may be more cost-effective for some shops to use flow bench data, dynamometer and track results to steer product development.” Which is probably why “this technology is more commonly found in large-budget racing series such as NASCAR and F1—and, of course, the OE manufacturers.”
That said, some large-scale aftermarket manufacturers are using it as well. Edelbrock of Torrance, California, uses CFD software to “design ports, combustion chambers and other shapes,” said Smitty Smith. “This allows our engineers to simulate the airflow in the ports, showing them where it is stronger or weaker.” Benefiting most from this technology have been “the lower classes and street classes, where the racer is not allowed to modify the cylinder head from however it comes out of the box.”
Still, several other manufacturers—even some fairly large ones—dismissed CFD, especially, as of little use for shaping the airflow inside a head, preferring to rely on experience and/or trial-and-error.
“You could say that computer modeling has led directly to better cylinder heads,” noted Bill Mitchell Jr. of Bill Mitchell Products (BMP), Ronkonkoma, New York, “from the standpoint that it really speeds the process from point A to point B. But in the end it still comes down to old-fashioned hands-on development to prove out and fine-tune the part. Machining capabilities have advanced, which allows for a much nicer part than in the past.”
Outside the Box?
Which leads to another interesting question: Are today’s CNC-ported heads so good that even a skilled head porter can no longer improve them?
“Today’s heads are the result of hundreds of hours of development work to maximize their performance,” replied Mike Downs of Trick Flow Specialties, Tallmadge, Ohio, “using advanced equipment not available to most engine builders. The aftermarket heads belonging to this new generation are so refined out of the box, it is very easy to hurt their performance by modifying them.”
“You certainly don’t want to increase the cross-section of the port,” added Scott March of Cylinder Head Innovations (CHI), Heidelberg Heights, Victoria, Australia. “Generally, with CNC-ported heads, enormous amounts of time have gone into the development and testing of the port. It would be advisable to leave them alone.”
The X1 cylinder head is a highly developed component that NRE considers to give a competition advantage “out of the box,” according to Renee Noonan of Noonan Race Engineering (NRE), Yatala, Queensland, Australia. “Team budgets and governing bodies rules become tighter every year. This reinforces the requirement for components to be race ready, as received.
“The ports in all our cylinder heads are always an evolving development, continually striving to improve, while listening to racers to meet their requirements,” she added.
When choosing a cylinder head, Noonan emphasized that flow numbers are only part of the equation. “Other features that improve reliability and Enhance performance are just as important. Features such as spring cooling oilers, priority rocker stand oiling, dedicated oil drains to prevent oil retention, pushrod size capability, should also be a consideration. When NRE design cylinder heads, the entire induction process is considered as a package, this is why NRE are now manufacturing billet intake manifolds to complement the X1 cylinder head,” she said.
Mamo believes that “any mass-production part can be improved. The question is to what extent. Where years ago a talented head porter might have been able to pick up a quality CNC piece by 15 percent, he may only be able to find half that percent gain now in some of the industry’s latest and greatest offerings. What was once acceptable and perhaps the industry norm a couple of years ago looks rough by today’s standards. On the other hand, just because a cylinder head comes off a CNC machine doesn’t automatically mean it’s an optimized or even efficient piece”—it can only be as efficient as the prototype on which the CNC program was based, he reasoned. “This is a widespread misconception. People hear that a head is CNC-ported, and they think it must be completely optimized, when that may or may not be the case.”
Feeney offered a slightly different point of view: “Today’s cylinder heads are designed to perform right out of the box; however, they are designed for a balance of performance, durability and economics.” Even engine builders “with a tremendous amount of head-porting experience” will often find this balance completely satisfactory. “However, some engine builders still have tricks of their own regarding valve jobs and valve profiles that they feel benefit their specific combination. This is why RHS offers both ‘p-port’ and ‘CNC’ versions of our heads, giving engine builders the choice of creating their own ports or buying a ready-to-run CNC head.”
“Of course, everything can always be improved upon,” added Mitchell. All of the cylinder heads from today’s reputable manufacturers are “good quality,” but that doesn’t mean they will work the same on every combination. “Why should we expect them to? We don’t expect the same camshaft to work in every combination. We’ll sell a pair of heads to a particular engine builder, and we’re heroes because they make 50 horsepower over what was on the engine previously. And then the next week we stink because the same heads did not produce the same results on a different engine with a different bore, stroke, camshaft, compression and carburetor. When building an engine, you have to go into it knowing not everything is going to be an easy bolt-on.”
“Remember that along with the advancements in ‘out-of-the-box’ technology,” said Patton, “we have also seen a dramatic increase in ‘head porter castings.’ The ability of head porters and developers around the world to begin with castings that have enough material in them to provide them with some options allows the industry to rapidly advance. In the past, porters had to take existing castings and heavily weld and modify them.
With today’s ‘porter’s castings,’ many more people have the ability to design race-winning ports.” Weld Tech in Brownsburg, Indiana, CNC ports a variety of cylinder heads, including some for drag racing. According to Chris Grace, Weld Tech works on new designs with its contracted port developers.
Grace explained, “With ‘out of the box’ cylinder heads, you are relying on the foundry to hold a tight tolerance with molten aluminum, compared to fully CNC porting the heads. When the molds that create the cores for the casting begin to wear, you will start to see a shift in cores. Repeatability would be the best addition we can strive for in prepping ‘out of the box’ cylinder heads. If you see that the castings are arriving with the same shift in the cores, we can at least repeat a shape using the CNC machine.”
He added, “The best way to stay legal with sanctioning bodies is to first establish a stream of communication with the associated tech department, then by submitting CNC prepped cylinder heads for approval.”
“With so many cylinder head choices available, today’s ‘out of the box’ heads are very good, but there is always room for improvement. To get the edge on the competition, extra porting and machining will need to be done; one size does not fit all,” noted Mike Androwick from Mike’s Racing Heads, Concord, North Carolina. “The size of the engine and rpm range dictate the size of the runners we design, not in volume, but in cross sectional areas.”
With its in-house 5-axis CNC machine, Mike’s Racing Heads is able to machine heads and intake manifolds with more precision and speed than ever, according to Androwick. “Utilizing solid modeling software also allows us to lighten our CNC cylinder heads as much as possible. A lighter car equals lower ETs,” he said.
Mike’s has a new CNC program for the popular Brodix SR20 casting that’s designed for 598–632 cubic inch engines. In addition, the company also has a program for “10-degree and 11-degree 4.500 bore space heads designed for large, high rpm cubic inch small block Chevys,” Androwick explained.
“We are making new cylinder head programs constantly as new casting designs become available. And if we can’t find a suitable casting, we can make the parts out of billet material,” he concluded.
Smith estimated that “for 90 percent of engine builds, Edelbrock’s completed heads represent quality and value that are unbeatable compared to a bare head you prep yourself. But for higher horsepower builds, where stock geometry can hinder airflow and combustion chamber efficiency, bare heads are more commonly used. By raising the intake and exhaust ports, airflow is increased, and the valve can be rotated to create a more compact combustion chamber. Huge power potential is unlocked, but everything—the pistons, valvetrain, and intake and exhaust systems— has to be replaced. Edelbrock works with the piston and valvetrain manufacturers to ensure that compatible products are available— and, of course, we have the intake manifold solutions.”
Finally, as Mitchell emphasized earlier, “there really isn’t any such thing as a bad head anymore”—not from the reputable manufacturers, at least. But there are “junk heads, copycat knockoffs of poor quality that don’t perform. You get what you pay for. How many people reading this have tried a pair of heads because the price sucked you in—and then had to spend hours relocating the rocker studs, bolt holes, etc. Or, when you checked the head’s position on the block from underneath, found that the chambers were not even in line with the bores?”
Go with the Flow?
Selecting a cylinder head, it seems, can be as complicated as engineering one. So we asked if flow ratings should be considered a priority during the selection process. “Published flow figures have been a topic of debate for many years,” Wilkinson replied. “If you look at valve placement, port shape, port area and volume, these will give you a much better idea of how a cylinder head design will perform. If the engineers have done their job sufficiently, the flow figures will be favorable. But by no means should flow numbers be high on your list” when choosing a head.
“Airflow numbers can indicate the potential for making power,” agreed Jack McInnis of World Products, Louisville, Kentucky, “but they don’t guarantee it. It really requires a lot of experience on the part of the engine builder to weigh all of the variables for a particular application.”
“Flow numbers are just a piece of the puzzle,” said Mamo, “but a very large piece, providing you know they are accurate, and that you have a good idea of how much flow you need to meet your rpm and power goals. Choosing the smallest head that flows enough to support your goals will always provide you with a better all-around power curve. Also, a head that flows a lot of air at a .900-inch valve lift is likely useless to an engine with a .680-lift cam. The proper combination has always been and always will be the most important thing to focus on. And if torn between two heads, it’s better to opt for the smaller one.” A too-small head will make better power than a too-large head. “And if need be, you can compensate for a slightly too-small head with a slightly longer-duration cam.”
Weinle emphasized the importance of “mid-lift flow. Look at the amount of time that the valve is open,” he said. “From .700 on up, the valve isn’t open that long. It’s open a lot longer at .500–.700. And what matters is how it fills the cylinder.”
Mitchell allowed that not everyone has the resources “to buy a handful of heads just to try them. So we ask people at the other end of the phone, ‘How much horsepower are you looking to make, realistically.’ Let’s say they want 700 hp. We can offer a head that has made 700 hp on a given cid with a particular stroke, compression, etc. And we can back those numbers all day long from our own engine program. We know the head can make at least that much because we know we’ve done it. We won’t speculate or guesstimate how much more it might make. So maybe the customer takes one of our own combinations as a blueprint.” But it’s still up to the customer to make the combination correct.
“Without context, flow numbers mean nothing,” added Patton. “Each engine will have an air speed requirement based on its size, rpm and intended use. Airflow is directly proportional to the size and shape of the ports. Seeking the highest efficiency through a given-size port and valve combination will generally make the most useable power. Unfortunately, most end users (racers) don’t have access to all this information, but they do have access to flow numbers, which have been misused as a marketing tool in the industry.”
“Airflow numbers are like dyno numbers,” said Maskin. “They are somewhat ambiguous and vary with different flow benches, air quality and corrected altitude. We recommend that they be dismissed in favor of the reputation of the seller to produce real-world results.