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reprinted from Automotive Engineering, June 1997

Honda/Acura NSX story is updated

Honda's NSX was hailed as one of the very best when it entered the world's super-car arena in 1990, threatening the supremacy of such established marques as Ferrari and Porsche. The seasoned rivals did not sit back with their reputations, but updated their products, the F355 and 911, taking them to new heights in vehicle dynamics and prestige.

The business environment has not been kind to the upstart as Japan's "bubble" economy burst and the yen's value soared, hurting exports. The ailment, particularly the latter part, affected other Japanese sports cars as well, and Toyota, Nissan, and Mazda pulled the MR2, 300ZX, and RX-7, respectively, out of the once-lucrative American market.

Honda persevered with the NSX, although its production was now only a fraction of what it used to be at its Takanesawa plant (where the bulk of work now is performing pre-delivery checks and preparation of Chrysler Jeeps which Honda sells, as well as building a small number of EV-Plus electric vehicles).

And now Honda has updated the NSX with a more powerful engine and detail improvements, and added two special, lightweight versions, the types S and S-Zero for the Japanese market (see cover).

Honda's powertrain engineers tend to design engines and transmissions "just right" for their original vehicle applications, light weight and compactness being paramount in their goals. This was true with the original NSX powertrain, which consisted of a quad camshaft, 24-valve, 3.0-L V6 and a five-speed transmission.

In the face of tougher competition, Honda found it necessary to give the NSX more power and an extra gear. Their engineers are also known for their ingenuity in squeezing things out of existing components, and that is what they did with the NSX powertrain.

The type C32B engine is an enlarged version of the C30A with its bore increased from 90 to 93 mm, retaining the original 78-mm stroke. This was done by adopting fiber-reinforced metal (FRM) cast in an aluminum block, instead of the type C30A's iron liners. This material combination was originally applied to the Prelude's 2.2-L inline four-cylinder block which had started out as a 2.0-L unit. The C32B thus gained 202 cm3, now displacing 3179 cm3. The engine block has shed 3 kg in mass as compared with the 3.0-L unit. The crankshaft and piston pin diameters have also been enlarged: the former from 50 to 52 mm and the latter from 22 to 23 mm.

The C32B employs Honda's VTEC variable valve timing and lift system on both intake and exhaust sides. The engine adopts larger intake valves, 36 mm instead of the C30A's 35 mm, and the fuel injector's flow rate increases by 15%. On the exhaust side, a pair of 3-into-1 fabricated stainless steel manifolds replace the smaller unit's cast iron ones, decreasing exhaust back pressure. Six pre-chambers are added to the muffler system to produce throatier exhaust sounds, according to Honda.

The C32B engine is rated at 209 kW JIS at 7300 rpm and a maximum torque value of 304 N·m at 5300 rpm. Not bound by Japan's curious voluntary restraint (maximum power is held to that level in catalogs), Honda claims higher output with the Acura NSX for the U.S. market.

A new manual six-speed transaxle is mated to the C32B engine. Again compact outer size was a mandatory design criterion as it would have to fit within the space occupied by the previous five-speed unit. For that, a single dry-plate clutch of 230-mm diameter replaces the previous twin-plate one of 190 mm, and the clutch disc uses a surface material of a higher frictional coefficient. The flywheel is now a dual-mass type, with split-mass pieces connected by inner and outer torsion springs, which effectively increases the transmission's inertia mass, and reduces shocks due to engine rpm variances and rapid acceleration. The lightweight S-Zero model is fitted with a single-mass flywheel.

A sixth gearset was added to the end of the gearbox, which employs narrower gears made of a high-strength steel alloy. Double-cone synchromesh is used on the lower four gears, enabling reduction of shift loads by as much as 40-50%. A reverse select lock solenoid prevents accidental shifting of the reverse gear. The solenoid engages the lock-in when the vehicle exceeds 30 km/h, and disengages it when it slows to below 25 km/h.

Gear ratios have been revised to exploit fully the C32B engine's performance. First and top gears are higher by 0.2 and 7.0%, respectively, compared with the five-speed gearbox, while intermediate gears have lower ratios, and are thus more closely spaced.

The automatic transmission NSX continues with the C30A 3.0-L engine which produces 198 kW JIS at 6800 rpm and 294 N·m at 5400 rpm. The transmission's manual downshift, using the paddle-lever on the steering column, is now faster, by 0.2 s in third-to-second shift and 0.1 s in the fourth-to-third downshift. This is made possible by electronic synchronizing of engine rpm, using the traction control computer's ability continuously to monitor real-time acceleration and deceleration.

The NSX's all-aluminum, welded, unibody shell has shed 2 kg by using an age-hardenable aluminum alloy which allowed thinner outer panels (1.0 vs 1.1 mm for hood, front fenders, roof, and trunk lid) and elimination of plastic reinforcement on the rear fenders. The body--in-white now has a mass of 208 kg. The aluminum alloys' properties are as follows:

1996 body 1997 body
Before paint bake
         Yield strength (MPa) 93 110
         Tensile strength (MPa) 194 215
         Elongation (%) 28 33
After paint bake
         Yield strength (MPa) 153 210

The door's outer panel, of the same gauge as before, benefits from the new alloy's extra strength, resisting dents that may be inflicted by people parked next to it.

The updated NSX is offered in three suspension settings, two of which are reserved, at least initially, for the Japanese market. The type S is a lightweight version, and the S-Zero is even lighter with less comfort equipment and primarily intended for "fun on the track."

Spring and shock absorber calibrations of these variations are:

Normal Type S Type S-Zero
Front suspension
         Spring rate (kg/mm) 3.5 6.5 8.0
         Stabilizer diam./thickness (mm) 18.3/3.0 18.3/3.0 18.3/3.0
         Shock absorber damping (N)
         rebound/jounce @ 0.01 cm/s 157/157 372/294 412/333
                                 @ 0.05 cm/s 431/441 735/588 1166/823
                                 @ 0.3 cm/s 1127/1068 1911/1470 3126/2215
Rear suspension
         Spring rate (kg/mm) 4.0 5.0 6.0
         Stabilizer diam./thickness (mm) 19.1/3.0 19.1/3.0 19.1/3.0
         Shock absorber damping (N)
         rebound/jounce @ 0.01 cm/s 402/265 372/294 412/333
                                 @ 0.05 cm/s 745/539 902/725 1225/862
                                 @ 0.3 cm/s 1793/1225 2254/1666 3087/2176
Vehicle Curb Mass (kg) 1350* 1320 1270

* C32B and six-speed manual transmission

Several function, comfort, and convenience items are deleted from the S and S-Zero, and some are replaced with lighter components. The former include: SRS air bags (not mandated in Japan), electric power steering, traction control, audio, cruise control, and the latter Recaro one-piece seats, BBS forged aluminum wheels, and in the S-Zero single plane rear partition glass, lightweight battery, and single-mass flywheel.

Larger brake rotors and rear-wheel cylinders are adopted in the brake system. Rotor diameters are now 298 mm front and 303 mm rear. The rear rotor's thickness has also been increased from 21 to 23 mm. The NSX is shod with front 215/45ZR16 and rear 245/40ZR17 tires on aluminum wheels.

As for add-ons, the NSX may now be equipped with discharge headlamps and a navigation system, except for the S-Zero, which is essentially an out-and-out track car.

Jack Yamaguchi