Honda's New Halo - Product Announcement

Automotive Industries, August, 1999 by John McCormick

"Lighter in feel than a Porsche Boxster, more like a Lotus Elise." Such lofty aspirations for a new sports car would be wishful thinking for many automakers, but not for Honda Executive Chief Engineer Shigeru Uehara.

In developing the new S2000 roadster, Uehara and his team set out to reaffirm Honda's reputation for engineering and technology. That reputation has become dulled in recent years, as Honda concentrated on popular but uninspiring mainstream cars such as the Accord.

With development virtually stalled on the exotic, expensive Acura NSX, attention at Honda turned to the more affordable roadster segment. In 1995, the company unveiled the SSM concept at the Tokyo show, and even though the sports car market was at a low point, company-President Nobuhiko Kawamoto decided to proceed with a production version. Four years later, the S2000 debuts in time to celebrate the millennium and (belatedly) Honda's 50th anniversary.

The car launches amidst a sports car rebirth, with successful entries including the Boxster, BMW Z3, Mercedes SLK and the now-classic Mazda Miata. Dan Bonawitz, vice-president of American Honda, believes the market sector in the U.S. will continue to grow through 2001 and level off at around 100,000 units annually. The resurgence, he says, is due to "baby boomers, reaching their peak earning years and, with their kids leaving home, who are looking to recapture their youth -- a time when they might have been driving MGs or Triumphs or one of Detroit's muscle cars."

Topping Uehara's list of desired attributes were high performance and first-class driving dynamics. But while rivals BMW and Benz cloak their roadsters in luxury trappings, the S2000 would remain a "true" sports car; like a Miata with a few extra frills.

Powerful and Clean

The S2000's character is rooted in an all-new 2.0L dohc inline 4-cylinder engine. The compact, all-aluminum unit develops a claimed 240 hp at 8,300 rpm and 153 lb-ft of torque at 7,500 rpm. It's the highest specific-output, naturally aspirated car engine in production, thanks to a superbike-like 8,900 rpm redline. But Uehara's team also designed in durability and low emissions, starting with a new version of Honda's familiar VTEC variable valve timing system.

"We used coaxial roller-bearing cam followers instead of the slipper-type in the existing design in order to reduce friction," Uehara explains. The cylinder block features fiber-reinforced metal (FRM) cylinder liners, which are lighter and more wear resistant than normal ferrous-metal liners.

The forged-aluminum pistons, a first for a Honda production car, have ultra-short skirts for light weight and low friction. Connecting rods and crankshaft are carburized and heat treated for durability. Ensuring a copious supply of cool intake air is a conical axial-flow filter, which sits in a large 5.5L expansion chamber located ahead of the longitudinally mounted engine.

To meet low emission vehicle regs, S2000 features a new metallic honeycomb catalyst, plus secondary air injection. The thin-walled metal converter takes the place of a typical ceramic design and quickly increases exhaust gas temperature, thus reducing hydrocarbon emissions. The new catalyst also makes 40% less back pressure than a conventional converter. Its fast light-off time is aided by the air-injection system, which uses an ECM-controlled electric pump to feed fresh air into the exhaust. The result is 40% lower exhaust emissions than are produced by the Civic Si coupe, claims Honda.

Bad To The X-Bone

To allow S2000 drivers to make the best use of the revs, a new close ratio 6-speed manual transmission routes power via a one-piece propshaft and CV joints (not U-joints) to the rear wheels. A Torsen limited-slip differential is standard. By using two parallel shafts in the transmission, loads on the gear synchronizers are reduced and the shifting effort is lightened. Double-cone synchronizers on flint, third and fourth gears, plus triple-cone synchronizers for the often used second gear, further improve shifting feel.

Throughout the car's development, emphasis was placed on making the S2000 as responsive to driver inputs as possible. This led Uehara to study how a driver rates acceleration "feel."

"Our tests showed that a driver feels acceleration response is `excellent' when the damping of acceleration G is rapid -- that is, when the time to reach steady G is short," he says. And the biggest factor contributing to this fast acceleration damping effect is the rigidity of the drivetrain, "especially the torsional rigidity of the driveshaft." As a result, the diameter of the rear half-shafts were enlarged.

A similarly detailed approach was taken with the brake system, which was modified by enlarging the master poppet valve in the master cylinder to give faster initial response to pedal application. "The pedal firmness is generally high in sports cars," Uehara notes, "but brake application effectiveness is low. For the S2000 we aimed to achieve both application effectiveness and pedal firmness."