Manufacturing for Performance Supplement: Hot Honing Improves Engine Performance
Greater longevity, higher horsepower, and reduced blow-by can result when the process is employed
By Frank Burke
In the competitive world of motor racing, success is often measured in minute increments. The top racing teams constantly search for even the smallest variable that can make the difference between a win and just another start. In defining that advantage, performance engine builders—and the suppliers who serve them—are continually seeking methods and materials that approach, but cannot exceed, the stringent guidelines set by NASCAR and other governing bodies.
A cast and machined torque plate is shown (left), while the torque plate prior to machining is at right.
A leading-edge process finding increasing acceptance among top-line competitive engine builders is the concept of hot honing, developed by C-K Technologies (Ballwin, MO), in cooperation with Sunnen Products Co. (St. Louis).
C-K Technologies provides modeling, gaging, design, and test services for engine builders and, according to the company's President, Harold McCormick, "Hot Honing was the natural outgrowth of the effort to remove variance from the boring process and get a better ring seal."
Thermal issues are important in racing. In the course of a race, as an engine block achieves operating temperature, the bore geometry undergoes a degree of distortion that can have a negative effect on the quality of the ring seal, resulting in a "horsepower leakage." In the C-K process, the head is attached, the block is heated to 220°F (104°C), and the bore geometry is measured with a precision gauge. The head is then removed, the unit is cooled, a specially designed Flow-Thru Torque Plate is installed, and the block is again heated to 220°F and measured. When the Flow-Thru Torque Plate has been validated, it's used for subsequent honing at temperature. According to McCormick, "The key to the operation is the Flow-Thru Torque Plate, which must duplicate the operating bore geometry created by the cylinder head."
Cast torque plates with secondary finishing are used for more popular engines. For lower-volume applications, torque plates with a center cast section and external stiffening plates are used. The stiffening plates are adjusted during C-K's validation process to provide the same bore distortion as the cylinder.
Sunnen Products Co. has supplied honing components to the automotive industry since 1924. Senior Product Manager Gerry Schnitzler and Senior Automotive Technician Tim Meara are both enthusiastic proponents of hot honing. "The industry has known for a long time that precision would be improved if the block were heated to operating temperature during the process," explains Schnitzler. "In fact, it has been tried in a number of ways, but the combined efforts of C-K Technologies' and Sunnen Products' engineering staffs resulted in a process with improved cylinder-bore precision, and eliminated a significant amount of the odor and smoke associated with previous attempts at providing hot-honed cylinder bores.
"We mated the C-K equipment to our top-line honing units, and recommended a diamond-based stone with a diameter range of 4-4.250" [102-108 mm] or 4.300" [109 mm] depending on bore size. Speeds vary based on the diameter and bore angles, but it's basically a low-speed process moving at 170 rpm and 60 strokes/min.
"The oil is a standard mineral-based honing oil circulated through the block cooling system and the torque plate top. Swarf is removed by a filtered cartridge system."
In addition to his work at Sunnen, Tim Meara builds engines as a hobby and has a connoisseur's appreciation for the hot honing process. "I think part of the challenge was finding a system that was practical over the spectrum of engine blocks and applications," comments Meara. "The system had to work with both cast-iron and aluminum blocks, and handle both big and small-bore through a whole range of racing conditions. At 220°F, some blocks can distort as much as 0.0035" [0.089 mm]. This distortion results in a void at the ring seal, and a corresponding loss of power. The hot-honing system represents a great leap forward, but its success depends on a number of factors including, and especially, accurate measurement of the bore and the development and utilization of validated torque plates."
Kroyer Racing Engines (Las Vegas, NV), supplies engines to the top names in professional racing. Before opening the shop, owner Kevin Kroyer was an engine builder with a leading off-road racing team. Located at the Las Vegas Motor Speedway Research and Development Center, the 10,000 ft2 (930 m2 ) Kroyer facility employs 15 technicians. "We build engines for customers running everything from the NASCAR Craftsman Truck Series to the Baja 1000 Endurance Race," Kroyer remarks, "and we even get into specialties such as the vintage Cobra competitions. We work with all kinds of blocks and materials, and it's our responsibility to give our customers the most up-to-date technology. We're always looking for what's newer and better."
Success in the shop translates to success on the track. At present, Kroyer's shop is equipped with a hot-honing station using C-K Technologies equipment mated to a Sunnen CK 21 honing system. "We typically take off 0.001" [0.03 mm] or less, depending on the application," says Kroyer. "In high mileage instances, we'll go from 0.002 to 0.005" [0.05-0.13 mm]. Generally speaking, the procedure is done on 40-50% of the engines we sell, but that number is growing." Hot honing is performed on new blocks prior to delivery, and again in the reconditioning process. Setup and procedure time usually adds about one hour to the conventional honing process.
"A few of our customers are aware that we're doing this," Kroyer observes, "but for the most part, it's transparent. It adds some cost, mostly due to the expense of the torque plates—which are sized for every different-sized block—but we find that it's been helpful across different applications. In some cases, it has resulted in higher horsepower. In others, we're seeing greater longevity. We look for the use of hot honing to become more widespread, and we know we'll employ it on more engines in the future."
Given all the variables involved in any given race, it's difficult to say that the precise removal of 0.001" of metal makes a difference, but McCormick is certain that it helps. "Dyno tests show a 1-2% horsepower improvement with the hot-honing process," says Harold. "In a 600-hp [448-kW] engine, that can equate to 6-12 hp [4.5-8.9 kW]—and that's a real advantage."
An avid racing fan, McCormick follows the teams equipped with hot-honed engines, and finds a statistical difference in wins-teams using hot honing consistently run ahead of their competitors.
Asked about the general implications of the process, he states, "I don't see this ever being used in the consumer car market, but we're investigating other areas where it might be effective. For instance, we're holding meetings with a number of small engine manufacturers who are looking for ways to eliminate blow-by to help achieve compliance with emission regulations." Talks are still in the very early stages, but if a variation of hot honing proves as advantageous for small power plants as it is for racing engines, there may come a time when your lawn mower has more in common with the NASCAR circuit than with your "stock" car.
Performance Demands Precision in All Components
The development of performance processes such as Hot Honing requires a team effort. As the technology has become more popular, engineers at Sunnen Products realized that the market for honing tools compatible with hot honing would increase. According to Mazak's (Florence, KY) Jack Halenkamp, "Even though this is a relatively low-production part, setup time is a real killer."
Working with Mazak distributor Bill Summers, a Mazak Integrex 300 multitasking turning center was recommended for the application.
"The Integrex 300 features up to 10 programmable axes—an advantage that eliminated much of the setup time," says Summers. Both the turning and milling spindles are powered by 35-hp [26-kW] drives that can operate at 5000 rpm and 10,000 rpm, respectively.
The hone body is machined from a 3-8" (76-203-mm) diam billet, depending on the stone size." During preliminary trials, machining time was slashed from 14 hr to 4 hr.
This article was first published in the January 2006 edition of Manufacturing Engineering magazine.