Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/126823
r-.. . ,. - ---- ----------------- --------------------, w l z ~ t:l « :::E c « a: a: [5 :::E ~ w :;: :J C U en [5 :I: C1. engine's limit of 20,000 rp m , the 250cc co uld be p umping o ut 170 bhp at peak - and still be flexi ble. So the two -strokes had better watch out. Purpose o f Schnepf's trip was to see the N R500 str ip ped down, the first time anyone outside Honda had seen th e in sid es o f th e radical V-four. H ere are th e first pi ctures pu blished of the insides o f Honda 's a mazing NRSoo ro ad ra cer - th e four-stroke Honda hoped would be th e twoat strokes in Grand Prix racing, just as . th ey had in th e 1960s. Ever since th e' machine first appeared in 1979 everyo ne speculated how Honda's engineers had been able to get so much power from a four-stroke en g ine - 135 bhp when the project was stopped in 1982 a nd all but th e details of its novel oval pistons rem a ined a secret, until no w. Obtaining eno ug h power from th e N R500 was neve r a problem fo r H o nda's engineers, but rid ing the bi ke was . At first it wa s dogged by unrelia bility - at its debut in 1979 a t Silverstone oil dropped - by one bike res ulted in Mi ck Grant dropping his N R500 at th e fir st bend. The bike cou ldn 't hav e had a more ignominious sta n. When th e troubl es had been ironed out th e NR500 proved it had speed . a nd Freddie Spencer raced o ne at Silver stone gamel y in 1982, three years after th e fir st a p pearance a n d pulled up to fifth pl ace. But ov ercoming th e bik e's excessive weight and ca p ricious eng ine beh a vio r was too much co m pared wi t h th e ease o f ra cing a tw o- st roke. The NS500 was far easier to rid e, a nd much lighter. But nothi n g wi ll rem ove th e m assive publicit y va lu e o f th e N R500 to H onda . T he co m pa ny is proud o f its e ngi neer ing tra d i tions and particularly o f its a bi lity to o vercome technica l p roble ms o thers would n ever tack le. That 's why pro vin g th e NR500 would eve nt ually become co m pe titive in th e face o f a lmos t uni vers al d er ision , and cri tic is m became more a battl e o f hon or than o ne o f si m p ly winn in g races. T he fact that th e esse nce o f th e engine lives o n i n th e form o f th e 250cc tu rboch arged developm ent p ro ject is p roof enough th a t H onda do esn 't th in k it wa sted severa l billi on ven o n the NR500. . T he 250 re tains th e l\'R500's oval p isto ns , not jus t to be di ffere nt (tho ugh th a t m a y ha ve much to do wit h it) but because it's possi ble to Iit eigh t valves into a ova l co mbustion cha m ber - a nd eigh t valves ca n flow more air tha n the four or fi ve that ca n be comfortably accom moda ted in a ro u nd co m bustion cha mber. The story o f ho w th ose ova l co mbustion chambers came into being sta rts back in 1977 . H onda 's presid ent Kawash im a had d ecided that th e co mpa ny would return to Gra nd Prix raci ng a nd a n a n no u nce me n t wa s m ad e a t th e launch o f the six-cylinde r CBX roadste r in Tokyo. Because H onda was famous for its four -st roke engines a nd had cl eaned up in racin g before pulling o ut at th e end o f 1967 , it felt th at it shou ld bu ild a four-strok e racer. The en g ineers in cha rge of th e racing project realized soon, however, th at a conventional four-cylinder. four-stroke wouldn't be a match for the two -stro ke fours . What they wanted was a n eight-cy linder engi ne but the FIM rules limi ted th e cylinders to four. Proj ect ch ief Shoich iro Irimaj iri, who had been a d esigner o n the race team in the 1960s a nd now was a H onda Motor Co. Director. set to th e ta sk o f trying to make a four-cylinder • work lik e a V-eight. o Final. 19 8 2 NR500 ve rsion used ca rbon -f iber frame. w heels and brake discs; ex haust was t itanium ; engine cas t ings magnesium. (Below) Each oval " cyli nder" has a two-ba rre l magnesium carburetor. and four intake valves. ~~Cil~GJ~~ ~~~~~14 ~~~(!)(!) \YJQ ~~W~ Honda's N R5 00 32-valve V-four, the machine that a lmost put fo ur-strokes .back on the Grand Prix m ap before it was a ba n doned in fav or of the world champio n sh ip -winnin g NS500 thr ee -cy linder tw o• stro ke, IS all set to mak e a co me back in th e form of a 150 16 . bhp turbocharged 250cc twin th at Fred d ie Spencer co u ld use in the 50Dec cla ss next yea r. H onda 's engi neers never d ro p ped th e p ro ject co mple tely - a nd are now cl ose to th e sta ge wher e th ey feel th e eng ine would be com peti tive against th e fo ur-cy li nder two-strokes in the 50Dec class (t here 's a 2-to - 1 ratio li mit fo r turbo Gra nd P r ix engines). R ecentl y Mor orrad m a gazin e ' s Wol fgang Sch ne p f (o f Wcst Germany) sa w the 250cc tu rbo H ond a fir st hand a t H ond a 's Asa ka, J a pan resea rch Iacil it v. And he found th at th e turbo is justas no vel as the N R500. As on th e N R500 , the 25Dec tw in uses ova l p is to ns with eigh t va lves per cy li nder. T he engi ne used fo r tes ti n g is a water -co ol ed ve rt ica l para lle l twin th a t's in effect th e V-fo ur with th e fro n t ba nk o f cy li nders remo ved. There are two tin y tu rbocharg er s, o ne for eac h cy linder , m ade a t Honda beca use no com pa ny ma kes a t urbo sma ll enough for a 250cc engi ne. In terestingl y, the test en g ine isn' t fuel injected: there's a carburetor o u tboard of the tu r bo s a lt hough a n engine management syst em which controls the fuel and ignition requirements of the motor is being developed in parallel. Honda Racing Company director Takeo Fuk ui, who a lso designed th e ' R 500 and th e two-stroke racers, is very excited about the 250cc tu rbo project . " It 's th e ri g h t co ncept fo r raci ng," he told Schnepf. " It doesn' t ha ve the heavy engi ne bra ki ng of t he NR5 00 and t ha nks to th e eight valves in each cy li nder ha s a bro ad rev ran ge a nd good to rque. " It 's a lso easy to stan, just like a two-str ok e," h e said. From firs t repor ts th e engi ne would sound as if it 's m a kin g m ore-than co mpeti tive powe r. Bu t if 150 bh p sou nds in cr edibl e for a 250cc engine, rem ember that a t a speci fic powe r o u tp u t o f 600 bhp per liter it d evelops roughl y th e sa me a mou nt as th e top F- I (ca r) turbo ra cing engines put o u t. The Porsche, TAG and Maclaren en g ines pump o u t 900 bhp from th eir 1500cc. Yet th ere 's still m o re to co m e from th e Honda 250cc turbo which h as diminutive dimen sions allowi ng much higher m echan ical limit s on its side. G iven m ore revs than th e c u rre n t 0