Cycle News - Archive Issues - 1990's

e.TECH Honda NR750 _ . 29-degree valve angle, with 20mm inlet valves and 18mm exhausts , and each elli ptical cylinder (there is a constant Curve to the shape, with no flat sides) has an effective bore of 75.3mm and two 8mm sparkplugs firi ng simultaneously - Kanazawa says they experimented with three plugs per cylinder, but there was no ben efit, even with the center plug's spark timed di££erently from the other two. Use of the oval pistons permits a 30% reduction in circumferenc e compared to two round pistons of equivalent combined bore, th us reducing sleeve resistance and thus friction by the same amount. Com pression ratio is 11.7:1 , very high for a street engine designed to ru n effic ie ntly on unleaded fuel, and acceptably close to the 12.5:I ratio of the racing NR7 50 (the NR500 had a compression ratio of well over 13:1, vary in g accordin g to th e various e The NR's illuminated digital speedometer sits above a carbon-fiber daShboard. The multipoint PGM-FI programmed fuel injection system uses eigh t injectors feedin g eight sep arate th rottle bodies and is controlled by a 16-bit microp rocessor. o versions of the motor). Achieving this kind of com pression with an oval piston design is not easy, says Kanazawa , because of the large amount of valve area, but H onda has achieve d it and at th e same tim e obtained the same degree of squish as on a conventional ro und-piston design: impressive. He a lso re veals that H onda h as also experi ment ed with differential timing of the various valves, in pairs and individually, but that th is did not reveal any performance benefit: " Hon estly, I must say we were surprised," he says. "The only advantage was in red ucing exhaust emissions, bu t th e NR750 is such a 'clean ' engine thanks to th e excell ent combus tion that we did not need to incorporate this. Therefore, all valves have the sam e timing in this version. " Two conrods per cylinder, each forged from an exotic all oy cockta il of titanium, vanad ium and aluminium, complete the cra nkshaft assembl y, incorpora ting a special surface coa ting to combat friction, resulting in a conr od 17% ligh ter than would otherwise be. Stroke is a sho rt 42mm; for life at 15,000 rp m. Optimum breathin g - fu rt her improved by a variabl e fresh air in let duct mechanism whi ch adj usts the airflow in to the large-volume (7.4 liter ) air cleaner in response to changes in engine speed - reduced friction and inertia, all accom p lished while at the same time minimizing engine bulk, and in creased piston speeds are the wa tchwo rds of th e NR750 design, . further refined with the fitting of a tru e electronic engine management system, of a kind h ith erto seen only on Ital ian mac hines in the two-wheeled world never in Japan. Developed for Honda by Den gshi Giken , th e multipoint PG M-FI programmed fuel inj ection system employs eigh t injectors feeding eight sepa rate th rottle bodi es, and controlled by a 16-bi t mi croprocessor which receives data from seven different inp u t sensors : cams ha ft tii!lin g, crankshaft rotatio n to provide p isto n position , in let air pr essur e, inlet ai r temperature, th rot tle posi tion, wate r temperature and atmospheric pressure . The full y-mapped system, lik e th e Web er/M ar elli EFI on Du ca ti or Bimota models , thus ensures optimum engi ne response and performance at all times . Maybe now other Japanese manufactur ers will follow su it , especially as H onda is likely to fit a simi lar system on the forthcom in g successor to the round-piston RC30. Though th e NR7 50 will never be raced if Honda can help it, it does have one feature wh ich could conceivably o n ly be o f u se in . competition: a cassette-type side-loading extractable gear cluster, mated to a very largediameter oil-bath clu tch with a spragtype reverse-torque lim iter, just as on the RC30. T hough Honda 's explana tion for extractable gear box is sup posedly 'to enable quicker ma intenance. Allow ing the tra ns missio n gears to be serviced without removing the eng ine is further proof of Honda's commitm en t to bu ild ing the riding machines of the 21st century (sic), th e ' tru e reason is they're just show in g off. I mean , if you were an NR750 owner and had pai d [38,000(po unds) for your two-wheeled design sta tement, wou ld you expect the shop to have to unload the gearb ox for any reason? Looks n ice on th e spec sheet, thoug h ... This revolutionary - and remarkably compact - po wer unit is housed in a chassis that, whi le outw ar dly mu ch mor e conventional, does boast some neat details of its own. Extern all y similar to' the RC30's twin -spar alloy fram e made from a com bination of fi ve-sided a nd tubu lar extrusi ons, mated to a forged Duralumin swingarm p ivot, it similarl y features a si n g le-si de d ELF-deri ved P roArm swi ngar m, but specially revised to match H onda's wat chwo rds of 'Dynamis m and Elegance' in the bike's handling. Well, send them a postcard if you can figure out what they mea n. But the meaty 45mm Showa u pside down forks and mu lti -adj ustable rear shoc k, each specially developed for the NR750 and bo th offeri n g 120mm wheel travel, bring new levels of sophistication to street motorcycle su sp ension. Sim ilarl y, th e 310mm front di scs an d 220m m rea r, each gripped by fou r and two-pis ton calipers respective ly an d aga in developed specially - this time by Nissin - for the b ike, supply state of the art stopping pow er. Honda has basically ensured that in return for its very high price (ap proxima tely '$60,000), th e NR750 customer will acquire a bike that has the finest componentry curren tly availab le, and that applies also to the specially-developed Michelin radial s, th e front a surprising 16-inch diameter 130170 ZR design which, however, ha s almost the same rolling circu mference as a current 17-inch p erformance tire , thus offering improved com fort and tra ction under braking, as well as a very round profile for progressive steeri ng. However, it' s the external appearance of the NR750 which most immediately impresses, and there 's no doubt the wind tunnel-developed bodywork, designed to produce maximum downforce at high speed as well as look good , is both striking and innovative in shape. The unique seat cowl shape plays its part in redu cing air turbulence, as well as du cting cool air to the twin stai nless steel ex ha u st silencers located in the tai l, shielded from the ems computer also located there by heavy shroudi ng. The wide but steeply raked screen is sp rayed with titanium to prevent scratchi ng and discoloration, as well as to provide dramatic visua l, cha nges accordin g to the light. With in the cockpi t, a carbonfiber dashboard hosts a com prehensive display of four analogue instruments with a wide 2700 . sweep, plus the an alogue rev-counter. Above this , a brightly illuminated digital speedometer with small er mil eage/trip gives instant viewing without deflecting the rider's eyes from the road as much or as long as is necessary with a conven tional instrument : th is is a gadget tha t works , and makes sense. T he NR7 50 oozes quality of execution from every pore, from the ultraexpensive deep , rich , red paintwork (it's only available in this single color), to the carbon fiber facing of the plastic bodywork , the £lap s hiding the sidestand when you fold it up, th e carefullyselected rubber used on the handlebar gri ps, the crepe urethen e used for the seat pad, and so on. Even the ign ition key embodies an original design in nic kel silver and carbo n fiber emphasizing the oval pis to n concept. No expe nse spa red, no deta il overlooked. A lot of mon ey, but a lot for your money. Yet while comparisons are inv idious, one set of da ta does serve to set the NR750 in cont ext. The oval-piston 'endurance racer wh ich appeared at the 1987 Le Mans 24 Hours delivered 157 bhp a nd wei ghed 347 pounds in endur ance form wi th ligh ts, a generator and starter motor , according to HRC boss T akeo Fukui. He's a man deepl y linked to the NR story: he was in charge of th e NR 500 race team tha t drea dfu l day they were thrown o££ the gri d of the 1979 Fren ch GP after nonq ua lifying, yet now as p resident of H RC and vice-pr esident of Honda R&D, he has had the ultimate satis faction of presiding over the NR750 's evolution in to the most exoti c and desirable street motorcycle ever pro du ced for sale to the public. Yet the street versio n of th is design delivers 125 bh p (100 bh p in some coun tries), and weig hs 489 pounds. Imagine what sort of bike H on da cou ld have produ ced (and still might!) if they'd decided to really blitz th e marketplace with an oval piston repli-racer. O'l

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