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/128644
run w ide ex it ing a tu rn hard on t he hard acc e leration , as th e Honda r i v a l s to rega i n t h e w o rld t i t l e m ore pl ent i ful s u p ply o f t h e top - gas - t here's no u nde rsteer, and it shook a nd waggled the bar s in f r om in 200 I , al though with the end powe r the bike a lrea dy ha s . B u t , as Ed w ard s ri gh t l y says , doesn 't p u s h the front wheel e v e n my hands long enough t o t ell m e new Ducati 996R Testastretta on the sections of drying tarm ac this was n 't j ust a po w e r wheeli e revv ing th e H ond a spen t its de ve lo p me n t yea r w here I c o u l d cr a c k th e thrott l e tha t w e n t wr on g . Ho wever , this Ev oluzi one ve r s i o n of Tro y Cors- with the new bike wi n ni n g t he wide open with i m p u n ity, wh i l e pro bably happened b ec aus e th e er's works April ia n ow up to World Cha mp ionsh ip and , j udgin g leaned h a r d over . stee ring damp er had bee n s l a ck- 12 ,700 rpm - both w ith s i m i l a r b y h i s perfo rmances in t h e fi nal e n e d ri ght o ff f o r the d a m p tra ck , s ho r t-s t roke engine dimensions two r ound s of the season in G e r - - e x i ti ng the Turn O n e an d n ormall y wo u l d n 't b e a fa c - t o t h e H ond a - HRC e n g i ne e rs will many and Brit a in , t h e R C 5 1 is all dialed -in , read y to defend its title . Nev e rt h e les s, o n a co u p le o f th e s e to 13,000 an d ho r se s h oe, a n d ag ai n o n th e l eft - tor . E v e r y w h e r e e l se, this was t he h av e to t h i nk hard a bo u t r aising hander a t t he to p o f th e hill - ultimat e g o od - m a n n e r e d race r - th e rev li mit at l e a st a no t her 500 ther e wa s s o m e i ns ta bili ty und er o n e th a t w ill be very ha rd for i t s r p m f or n e x t se aso n , t o pro v id e a Tech: Building A Better Twin "We haven't had a singl e m echanical fail ure all year long ," says Colin Edwards' race engineer, Kiw i A dri an Gorst, who together with hi s Britis h -based Castrol Honda team colleagues is respon sib le for building the engines Edwards used to win the Wo rld Superb ike titl e - naturally , to HRC specification, of course - as well as ma intain ing them in race-winning condition. But arguably even m or e of a surprise - especially by the stand ards of other, shorter-fused V-twin Sup erbikes of th e Latin persuasion · is the amaz ing longevit y of the RC5 1's main engine com ponents. "T he engine has a 2700 km . (16 74 m iles J life betwe en stripdo wns ," say s Gor st, "so th at' s several rac es on the go before we need to pu ll it apart and repl ace any th ing - but never anything m aj or. Crank cases hav e lasted one full season, and so have crank shafts and cy li nde r heads. Col in raced at Br and s Hatch in Oc to ber with main engine co m ponents he used in the fir st round at Kya lami, back in April. " This robust engi ne li fe augurs well for when eventuall y Hond a does decid e to offer a similar level of performance to the Castrol wor ks bikes to privateers, rath er than the some what detu ned kitbik es used by custo m ers this season - but it also explains the Japanese V-twin 's am azing qualities as an endurance rac er , even in th e succession of eiqht -hour -long sprint races th at com pri se the Suzuka Eigh t Hours . In fac t, th e development of the race-winning Uk awa/Ka toh Eight-Hour bik e pl ayed a cru cial role in cl inc hi ng the World Superbi ke title , as Ad rian Gor st exp lains. "W e had four di fferent engine specificatio ns during the course of the season," he says, "w ith the firs t one at Ky alami the same as what we'd run in winter testi ng. Th at had steel conrods, but for the seco nd round in Aus tra lia we had Sp ec 2, whic h had tit anium rods, but was otherwise the sam e. We got Spec 3 for Monza, but didn't race it till Hoc kenheim , and though th is ga ve a little m or e po wer at the to p end, tha t wa sn' t the poin t of it. We felt we had a tracti on pro blem with Sp ec 2, whi ch Hond a tried to resolve via different cam shafts and piston s, to c reate a sm oother power deli very that stopped it spinning up in the m iddl e of the corner, so yo u co uld carry m ore co rne r speed . But as Colin's just ex plained (see sideba r). th is broug ht other handling problem s with it - so for Laguna we reverted to Spec 2, and tr ied to fix these. Meantime, we'd tested in J apan with the special engine they'd developed for the Suzuka Eight Hours, and though we said we didn't want thi s for sprint raci ng in Wo rld Superbike , Honda modified it a little and produced Spec 4 for Assen . We didn 't race it ther e, but did do at Oschersleben and Brands - so it's won thre e out of its fou r races , and alm ost had a 100 per cent reco rd, especiall y if yo u count Suzuka . Basically, it' s a combination of the Eight-Hour eng ine and ou r Spec 2 , on ly with a bett er power deli very and incr eased com ponent strengt h." T he 90 -degree V-twin eight -valve DOHC engi ne naturally follows the RC51 streetb ike in me asuring 100 x 63 .6 mm, for 99 9cc, with cam drive via a train of three gears driv en off the end of the crank, operati ng the tw in overhead cams hafts in each cylinder head . Th e bigg er bore allows a set of oversiz e valves per cyli nder, each wi th two valve springs and set at a flat inclu ded ang le of 24 degrees to each oth er. These are all made from titan ium, as are the connecti ng rods on the Spec 4 engine employed in the test bike, fitted wit h thr ee-ring pistons after Honda suffered oil -blow- by problems in testin g with tw o-ring ones. With oil con sumption a fac tor in the Suzuka Eight Hours, HRC engineers opted to stick with the thr ee-ri ng ones in devel oping the race engine, whi ch is essentially the same for both endu rance and sprint raci ng. Unlike on the RC4 5, whose Eig ht -Hour version had a slightly softe r state of tun e, the two typ es of SP-IW/RC 51 racebike have the sam e engine specifi cati on , but with the Eight- Hour bik e's EFI set up leaner in order to spa ce out fuel stop s, and the rev lim iter set 250 rpm lower than the Edw ard s 12,000 rpm cuto ff, for reli abili ty . This m eans th at, running on the same 12.8 :I co m pressio n and fitted with the same Ak rapo vic ti tanium exhaust , bo th bik es produ ce all- but the sam e hor sepow er - 10 hp less than the last version of the RC45 , accord ing to Honda sources . Th at m ak es it 18 1 hp at 12,000 rpm , accor ding to my records - some go ing for a V-twin, especially when combined wi th the ki nd of twi n -cylinder ri deabil it y that allows th e RC51 to lap a seco n d fa st er on alm ost every circuit than its mo re pow erful V-four predecessor. In term s o f top speed, the two are almos t identic a l, wi th t he RC5 1 trapped at 190 .96 mph , una ssisted , at Ho c k en hei m thi s y ea r j ust as the RC45 was in '9 9. While th e pair of Keihin throttle bo dies fitt ed to th e street RC51 m eas ure just 54m m, t h e work s ra c er s use 6 2mm > It s ho u ld b e a great Batt le of the eN T w in s in 2 00 1. versions on the ir PGM FI fuel-inj ecti on which, li ke Ducat i' s overs ized 60 m m equiv alents are specia lly hom ol ogated for World Superb ike vi a the cus tomer race k it. As on the RC45 , these incorporate twin inj ectors per cy linder, set op posite each other before the throttle butterfly, but for the first ti m e on a Hon da Supe rbike , the RC51 is fitted wi th a fully inte grat ed engin ema nage me nt system inco rpor ati ng the EFI , so that the whole EMS/EFI pa cka ge can no w be reprogram me d in real tim e by pl uggi ng in a laptop com puter. The street airbox has been substantially increased in size via a k it part on the racer, though is still, of co urse, fed by the same tri angular central airdu ct in th e nose of the fair ing , wh ic h m akes the RC5 1 look so m uch li ke a Ducati Superm ono on stero ids. As on the streetb ike , this flow s air to the thro tt le bo dies via duc ting cleve rly incorporat ed in th e alloy steering head casting of the chass is, all aim ed at deliv ering as straight a hit as possible of coo l ram air to the airbox , while kee ping the bi ke as slim and aerodynamic as it can be, 356.5 pounds] half-dry weight li m it, the Scali ng a kilo over the World Sup erbi ke 162 kg . 1 Honda und oubtedl y went on an effective diet at design st age, t hou gh t he fac t tha t thi s is split 53 /47 p erc ent fro ntwar d and delivers a m ore centralize d ma ss than t he D ucati' s L-tw in design, is even mor e of a bonus in t erm s o f handling. Th ou gh both bikes hav e a 9 0 -de gre e cy li n de r ang le, the fa ct tha t th e Hond a has the cy li nders m ov ed fu rth er aro u n d the c ra n k c a se s co m par ed to its Italia n ri val, helps achie ve th e m ore favora ble weight b ias , e ve n i f t he g ear - d r i ve engine is ph y sicall y b igge r than the belt -drive desm o mot or - adding furth er credit to Honda's feat in making the SP-IW so sma ll. An d worth noting too that, like the VTRIOOO, the SP-IW's engine design sees the cylinder castings integ rated with the upper hal f of the horizont all y -sp lit crankcases, for extra strength , Lik e Duceti, though, Honda has troubl e push-startin g the V-twin in pit lane becau se of the slipper cl utc h (aka 'ba ck torqu e limiter' ) fitted to the tr ansm ission to stop the rear wheel hop ping und er revers e loads on the overrun when bra king for a tum - so rather tha n m ess with the rem ote rear-wheel fricti on st arte r pow ered by a law nmower engine that all Ducati race teams employ (and which, of co urse, requi res the bik e to be parked on a stand with the rear wheel off the gro und, to do so ), Hon da has sim ply left on the streetb ik e electric start to facil it ate fi ring up the motor - even on the Wo rld Superbike racers , let alone the endurance versio n where this would be a prer equ isite. As Aprilia race boss Giuseppe Bern icchia has already remarked rather wistfu lly , Hond a engineers must have wo rk ed very hard to allow them selves the luxury of the electric st art, wi thout any weig ht penalty . To creat e th eir V-twin Superbike, Honda j ett iso ned their p reviou s so -ca lled ' Pivotl ess' frame co nce pt and reverted to their trad iti ona l extruded/cast -alumi num tw in -spar chassis, but w ith th e bra ced , dou bl e-s id ed , fabr icated alloy swin g arm p ivoting in bo th th e en gine crankc ases and the lower frame casti ng , which is also braced with an allo y cross -m em ber. Th e team ru ns different length swingarms depend ing on th e ci rcuit - in th e Br and s Hatch guise I rod e the bike, th is resulted in a quite rangy 142 7 mm wheelba se, though for Kyalami the length went as high as 1431 mm, and for other circ uits can be up to J 2mm short er. The purpose of all thi s is to alter the weigh t distributio n for an optim um balance between frontwheel grip, st abili ty and ease of turn ing, without changing the rear rid e height and so upset tin g the steering geo me try , Th e fully adju stable 47m m Show a race forks (same as on the RC45) are set in the frame at the stock 24 .5 -degr ee head angle . and Coli n usually run s arou nd 96 -99 mm of tra il - quite conservative steering geometry by racer standards, in keeping with his quest for stabil ity . Th e brake package has also been sourced from the RC45, with 320mm front Nissin discs gripped by th e J apanese firm 's six -pot ca lipers, and a tiny 196m m disc tha t the Texas Tom ado hard ly ever uses. Though 17 -in ch rain rubb er was perforce fitted for ou r test, Edwards usua lly raced with Mi chelin 's new 16.5 -inc h fro nt tire in the dry, opti ng for its extra gr ip at th e co st of redu ced feel from the front end . At the rear, he swit ched betwe en both sizes in the dry , using the 17 -inc h tire that gives m ore grip but goes off sooner at tr acks lik e Ky alami , Donington and Brands Hatch, where being able to accelerate harder on the ang le is a key factor , Ot her wise, he stu ck with the 16.5-incher, for ext ra durabil ity , While the Honda engine's rob ustn ess m eans th e team's seen less of the inside of th eir RC5 1 motors than other V-twin Superbike team s do, it 's an easy bi ke to wor k on . says Ad ria n Gorst, "T he engine design is very sim ilar insi de to th e RC45, in term s of layout," he says, "It' s as if it was bored and stroked, then cut in half - it' s been well thou ght out , and the bott om end design is very sim ila r to the V-four. Reall y , the fact th at it's won the Wor ld Sup erb ike title, two of the three m aj or World Endurance races, plu s a lot of American Cham pionship rounds, is a real tribute to th e design sk ills, the development and th e hard work pu t in by HRC staff in m aking it so good straight awa y . We'r e at the sharp end in the Castrol Honda race team - but witho ut those guys behind us , it co uldn't be don e. Th ey 'v e delivered us a product whi ch Coli n has proved to be the best in the world ." e y e ' e n e 1IV S • .JAN UARY 3, 2001 37