Nikasil plated cylinders enhanced engine durability and the ATAC valve produced a wider powerband.
The NS500 was ridden by Takazumi Katayama at the 1982 Yugoslavia GP. In the middle of its debut season, Nikasil-plated cylinders were installed to improve engine power and durability. (Photo/Shigeo Kibiki)
In August 1981, the first V-type 3-cylinder test engine was completed only seven months after the launch of development in January 1981. Another half a year plus later, in March 1982, the NS500 made its World Championship debut at the Argentine GP, the opening round of the series.
The early NS500 was troubled by piston and cylinder seizures in its engine due to heat and distortion. To prevent such events, engine designers planned on increasing the number of stud bolts from four to six per cylinder and installing an independent sleeve inside the water jacket. These structural changes to the cylinder went nowhere, but they solved the seizure problem by utilizing a new technology to the sliding surface of the cylinder.
Early on, Honda used a special hard chrome plating for the cylinder of the NS500, which they applied from the technology developed for the preceding 4-stroke racer, NR500. To be specific, the hard chrome plating was applied by running an electric current in the opposite direction to create fine cracks intentionally on the sliding surface so that they could hold enough oil. However, when the throttle was suddenly closed from wide-open condition, the temperature of the combustion chamber decreased so much. It became apparent that hard chrome plating was not sufficient to deal with the deformation of the cylinder and to overcome potential weakness of the 2-stroke engine.
Among various technologies explored by the engine designers at Honda, Nikasil plating was found as an influential solution. This technology from West Germany showed a favorable result in the test, and became one of the deciding factors in actual racing from the middle of the 1982 World Grand Prix series. Since then, the engine seizure problems had been reduced thanks to the Nikasil plating.
In the primary stage of development, the NS500 had issues in its engine performance. It had weak torque at the bottom and a narrow usable powerband. Although it was a part of unavoidable phenomena for a high-revving 2-stroke engine, rival manufacturers with years of experience had developed devices that compensate for low-rpm torque.
Honda was a latecomer to the 2-stroke, and in 1982, the first year of the NS500, they had no choice but to race with a simple engine without any exhaust device. However, in 1983, the second year for the NS500, its engine was equipped with a device called ATAC (Auto controlled Torque Amplification Chamber) by utilizing the exhaust pulsation effect. The ATAC became also in practical use among the 2-stroke street bikes and motocrossers later.
The 1983 NS500 which was newly equipped with the ATAC to compensate for its weak low-rpm torque, won half of the races at the World GP series that year thanks to Freddie Spencer's riding. Honda's long-cherished dream of winning the riders' title in the premier class came true. (Photo/Shigeo Kibiki)
This mechanism, often called the "ATAC valve," is a device that has a sub-chamber at the end of the cylinder's exhaust port that opens and closes the inlet valve depending on the engine speed. At low rpm, the valve opens and the exhaust (strictly speaking, pulsating pressure waves) flows into the sub-chamber, preventing the intake (air-fuel mixture) from blowing out of the cylinder without being ignited. At high rpm (over 7000 rpm for the NS500), the valve closes and the exhaust flows only to the main chamber, producing power with the original specifications of the exhaust pipe.
The ATAC for the NS500 first appeared in 1983, installed on the upward facing cylinders No.1 and 3. From the halfway stage of the Grand Prix season, it was also equipped with the downward facing No. 2 cylinder, which became a powerful card to strengthen the competitive ability of the NS500.
Chassis continued to evolve finely
Switched to an aluminum frame halfway through the first season
A naked NS500 without the cowling and fuel tank. The double cradle frame was the standard for high-performance road racers from the mid-1970s to the early 1980s, but the NS was the last one to use it for Honda's GP500 works machine. In the photo is a 1984 NS500 ridden by Freddie Spencer, which is stored in the Honda Collection Hall. (Photo/Shinpei Suzuki)
The ideal example of chassis of racers should not change so much depending on the engine type whether it is a 4-stroke or a 2-stroke. So, the chassis of the NS500 was developed by making full use of the NR500, the pathfinder in the GP500 road racing, which enabled a wide range of evolution in a short period. The basic form of the main frame body and the rear suspension type were consistent with the NS500, Honda used a double cradle type frame and an epoch-making suspension named Pro-Link. However, their specifications came in a variety and it depended on the type.
The NS500 could be classified into four types as follows.
NS2A-1X: the prototype
NS2A-2X: the early 1982 type
NS2A-AL: the late 1982 type
NS2B: the 1983 type
Each one had different specifications.
Spencer's machine at the 1982 Argentine GP, the NS500's World Grand Prix debut. The tire rim diameter was 16 inches at the front and 18 inches at the rear. The frame was made of steel round pipe, and the red paint was derived from Honda's motocrosser at the time. (Photo/Shigeo Kibiki)
The frame body was made of steel round pipe up to NS2A-2X. The NS2A-AL which debuted in June 1982, basically had the same layout, but was made of 30mm x 30mm aluminum square pipe, and the NS2B in 1983 followed suit. Meanwhile, the rear suspension of the prototype NS2A-1X was a bottom link type with a link pivot on the swingarm, but the NS2A-2X and NS2A-AL that ran in the 1982 season used the swingarm bridge for the links to be placed on the upper side of the part. The NS2B used a modern bottom link type with a single tension rod with a large cross section.
One of the distinctive features of the NS500 chassis is that it was designed to use a rim diameter of only 16 inches for the front tires in order to achieve a compact chassis with low center of gravity. On the other hand, 18-inch rear tires were used throughout the 1982 season, but 16-inch rear tires were standardized for 1983. The outer diameter was almost the same as 18 inches, but the width was much wider. They were trying to increase the width of the contact patch during cornering by using 16-inch rear tires.
