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reprinted from Automotive Engineering, August 1989

New valve technology from Honda

Honda has adopted the new variable valve timing and lift system (AE January 1989) in upper Japanese versions of the recently updated Integra series of small cars.

As promised when the working principle was first revealed some months ago, the new type B16A twin-cam 16-valve inline four-cylinder engine is a 75-bkW-per-liter unit, producing 120 bkW JIS net from 1595 cc and without the aid of a super- or turbocharger.

The B16A engine is a completely new design, sharing no components with the existing ZC 1.6-liter unit offered in single and double overhead camshaft designs, both featuring four valves per cylinder. To the ZC's long-stroke internal dimensions, 90-mm stroke to 75-mm bore, the B16A is an oversquare design with 81-mm bore and 77.4-mm stroke. On a high 10.2:1 compression ratio and with Honda's PGM-FI electronically controlled fuel injection, the 1595-cc unit is rated at 120 bkW JIS net produced at a high 7600 rpm and puts out a maximum torque of 152 N·m at 7000 rpm. The engine is redlined and governed at 8000 rpm.

The four-valves-per-cylinder are Vee-inclined at an included angle of 56° in a pentroof-shaped combustion chamber. Valve diameters are 33 mm for intake and 28 mm for exhaust. There are three cams and three rockers per pair of valves. The cams have different profiles and lift amounts. On either side are "primary" or low-mid-speed cams, flanking the lone "secondary" or high-speed cam. Obviously the secondary power cam has a wider opening period and a higher lift: a 90° overlap and a 10-mm lift, which is indeed similar to those of a Group A racing Civic. The primary valves have milder timings and smaller lifts, the latter 8 mm and 5 mm. One of these primary cams, the 8-mm lift one, operates its intake valve first via rocker arm, letting mixtures in and generating swirl motion. The other 5-mm lift primary cam-valve combination follows 10° later, further filling the combustion chamber.

While the primary cams are opening and closing the valves, the center cam and rocker are turning and moving, but are disengaged from operating the valves. At higher rpm and higher load conditions, a hydraulically operated piston pushes in a two-piece pin interconnecting the three rocker arms in unison, which are now operated by the center power cam that opens the valves longer and lifts them higher for producing more power. Interconnection of the three rocker arms is controlled by an ECU that gathers signals on engine rpm, load, vehicle speed, water temperature, and other relevant data. The switchover between the primary and secondary cam operations is variable, dependent on load and rpm. For example, with intake manifold vacuum of -20 mmHg, the secondary power cam comes on at 4800 rpm, with -100 mmHg at 5000, and optimum -300 mmHg load at 5200 rpm. Anything below, the primary low- and mid-range cams produce ample torque and tractable power.

The same engine, mated to a new four-speed electronically controlled automatic transmission, is tuned differently, with emphasis on low-end torque characteristics. It is rated at 112 bkW JIS net at 7100 rpm and produces a maximum 150 N·m torque at 6000 rpm, with the engine redlined at 7500.

Metallurgy is one area Honda has learned well from its racing activities, which culminate in the International Formula One category (in fact the VTEC engine's chief designer was engaged in earlier F1 endeavors), and its lessons are applied to the VTEC engine which, with its higher-than-normal output, is obviously subjected to higher thermal load and mechanical stresses.

The aluminum cylinder block is a closed-deck, deep-skirt design for high rigidity. The transmission side of the block is heavily reinforced to improve total powerplant stiffness. Iron liners are cast in the block. The forged steel crankshaft carries eight counterweights, its journals are finely polished, and it is supported by mirror-finished main bearings. The crankshaft is fitted with a torsional damper within the accessory drive pulley. Lightweight pistons and connecting rods are used in the new engine; the insides of the former are oil-jet cooled. Camshafts are of Honda's new cast steel alloy with high carbon and chromium contents. Valves are also of new heat-resistant alloy with molybdenum and titanium additions.

The B16A engine and transaxle power unit has gained some 20 kg over the previous ZC DOHC 1.6-liter four; however, the increase in the valvetrain weight is relatively modest at 6.3 kg, despite the increased number of cams, rockers, and actuating mechanisms.

Integra models destined for the American market will come sans VTEC, but with a couple hundred cc added to its displacement. Philosophy here is "more cubic capacity to attain designed effects," which include generous low- and mid-speed torque characteristics.

In addition to the close-ratio five-speed manual transaxle, Honda offers a new electronically controlled four-speed automatic with the B16A VTEC engine. This is an entirely new unit, featuring three shafts, whose primary purpose is to shorten the transaxle assembly so that it fits in line with the engine.

The updated Integra's chassis follows the recent Honda design practice in that it adopts unequal length arms ("double-wishbones" as the Japanese prefer to call it) independent suspension at front and rear. The Integra features longer suspension travel for improved ride quality. A new vehicle speed-sensing power steering is offered as standard equipment on the VTEC-powered models.

The new Integra is available in three-door coupe and four-door sedan guises.

Jack Yamaguchi