Cycle News - Archive Issues - 1980's

after awhile, even if cleaned before a race . Strange, but true. The effect of th ese internal modifications has been to tak e th e en gine to th e lim it of th e 750cc class capacity with 0.3mm oversize 68.3mm pi stons giv ing 12:1 co m pression; to develo p a ran ge of ca ms hafts to g ive th e o p tio n o f va ryi ng powe r characteristics to sui t d ifferent ci rcui ts by a lte ri ng va lve timing , lift a nd dwell; to increase va lve sizes on th e 20-va lve DOHC motor by lm m over sta nda rd to 24mm inlet a n d 22mm ex ha ust; a nd above a ll, to m aximize th e benefits o f bein g th e o n ly fourcy lin der team to em p loy Web er/ Marelli E FIIE MS, thanks to its homologation on th e YR4EI ro ad bike. H ow ever, in op ti ng for th e electronic fuel inj ecti on ro u te, Bimota has logi call y ta ken advan tage o f th e han ds-on experience in electron ics to extend th eir degree o f compu ter iza- . tion to th e point that on ly Kenn y Roberts' Luck y St rike Yamaha GP team . is as far adva nce d a lo ng th e elec tro n ic data-gathering road. At the Canadian Superbike round at Mosport earlier this year, Birnota d ebuted the real -tim e d at a acq u is ition sys te m th ey 'v e been u sin g in test ing since th e sta rt of th e yea r, developed in co nj u nc tio n with Marell i a n d employ ing a n IBMco m pa tib le Toshi ba MS DO S computer with a n It a lian D igi tech so ftwa re package. T his not on ly ena bles th em to mon itor th e EFII EMS setu p by plugg in g di rec tly into th e on-board co m p u ter, bu t to ob ta in a host o f other mat eri al mostl y, but not excl usi vely , relating to chassis behavior. The principal data Marconi likes to work with incl udes suspension travel from and rear, steerin g lock, speed and acce lera tion which , when combined with readouts of the angle of th e throttle butterflies a nd rpm tell him j us t about every th in g h e needs to kn ow about th e bike's co m port ment a t a ny given point of th e track or moment in time. Add in th e ability to monitor th e eng ine's oil temperature and exh au st port temperature, co m bine it with the data supplied and contro lled by th e EFIIEMS, and yo u have th e cap ability to determine how th e en gine is behaving, at the same time. Th e Web er /M arelli EF IIEM S e m p lo ys a si ng le inj ector p er cylinde r, a n elec tric fuel pump, a n d a n on- board co m p u ter co n ta in ing th e single EPROM ch ip , mounted o n a ca rbo n -fiber panel under th e back o f th e sea t where it does not a p pare n tly su ffer from vibra tion induced problem s as has been th e case with sim ila r Web er /M arelli co m po ne n ts m ounted o n MOIO Guzzi a nd Du cati twins; perhaps th e four-cylinder engine of th e Bimot a is tha t much sm oo ther. The EF I/EMS is known as th e ALPHA NP system, after its three fund am enta l parameters: Alph a = th rottl e butterfl y a ngle, N = rpm, a n d P = state o f fuel deli very . T hese in turn a re a ffected by tw o secondary parameters, namel y ign ition advance a nd inject io n tim in g, a nd sensors are filled which monitor a ll of these fun cti ons, as we II as supp lying data o n wa ter tempera ture, a ir pressure a nd tem pe rature inside th e airbo x, a nd th e battery volta ge: if this varies up or do wn from th e 12-volt norm, it a lters both th e ignition advance and injectio n timing, so it 's q ui te critica l a nd a co m pe nsato ry fun cti on h a s to be built into th e system. T he on -boa rd co mp u te r acq uires a ll this data, p rocesses it , a nd co ntrols th e fuel i n jectio n fun c tions acco rdi ng ly. Now do yo u see why it's ca lled an engine managem ent system? British journalist Alan Cathcart rode Giancarlo Falappa's Bimota Superbike at Rijeka. Yugoslavia. Being a factory team with close re la tio ns w i th W eb er /M a rell i , Bimota h as th e ability to cook th eir own EPROM ch ips off th e bike w ith the Toshiba (tho u gh they don't yet have th e works Du cati .tearn 's latest goodi e, wh ich is a h and l ebarmounted , three-way switch ena b ling th e rider to switch between three different ch i ps o ut o n th e circ u itl), as well as to fin e tune them o nce installed in th e bl ack box (ac tua lly, it 's silver) via a portable p rogrammer wi elded by Bruno a nd Massimo , th e ' wor ks race m echani cs. H o wever , ha ving once su p posedly perfected th e engi ne's runn ing to the n th degree in th is way, it's importa nt no t to sta ll o r cut th e moto r si nce by doing so you retu rn th e setti ngs to thei r origina l po sit ions. Ca re fu l h ow ou t th e cl u tc h, yo u let Giancarl o .. : ! Birn ota brought both Falappa 's race bik es to Rij eka for testi ng - one in standard '89 form with Ohlins inverte d fro nt forks, th e o ther with p rototype racing versi ons of the Marzocch i u p side do wn forks n ow filled to the YB4EI roadster, as well as Man occhi rear suspe ns ion instead of th e normal Ohl ins rear un it. A more dramatic-looking m od to be tried o u t a t th e test day was the p ro vision o f two Kaw asaki ZXR-type ai r-i nd uc tion tra cts leading through th e lank shro ud to th e ai rbox, since in dyn o testin g Mar coni h ad de tected a p ower increase wit h th e ram air effect th ereby ob ta ined. T he res u lt was u nkindl y dubb ed "Big Ears" a nd si nce it h appen ed to be closest, I wen t ou t on it first. If I was half expecting to find myself aboard a faster, bet ter-braked version o f the YB4EI roadster, I was in fo r a big surprise. In the th ree years since I last -rode a Bimo ta factory racer, th e wo rld o f four-stroke ra cing has ch a nged im measu ra bly, leastways seen from Bimota 's co rner o f th e ring. ' Forget about Superbike racing su p posedly being abou t m odified ro ad bikes, a sort o f.su pe rstree t Silhouette class: the YB4EIR is a GP racing motorcycle that just happen s to have a four-stroke en gin e in it . In a way. this is a reflection of th e cha nge in the kind of racing organ ized a t world level for four-st rokes. Befo re, th e acce nt was o n 'IT FI , w hich predica ted lon g e r races, mostly ove r road circu its, with a grea ter variety of surfaces a nd a n acce n t on rid er comfort . Now, th e World Su perbi ke Series entails two short , sharp, furious races per round, n ot even as long indi vidualI y as GPs, a n d h eld o n " p ro per" GP-styl e circu its (yes, well , plus Mo sportl ). The bikes have cha nged accord in g ly. So , apa rt fro m th e curious riding p o siti on d ic tated b y Falappa ' s h ighly in divi d ua l upri ght style, with th e bars - themsel ves lo nger th a n usu al , as befits a form er "crossista" - sprea d very wide a n d n at, just like on o ne o f Rob McElnea 's bik es, th e firs t th ing you n otice abou t th e Bim o ta is h ow far forward yo u sit on it, j ust like a current 500cc GP race r. Falappa, who 's a bo ut the sa me he igh t as me, har dl y ever ge ts flat o n th e tank, b ut if he did h e'd fin d hi s chi n making fri ends with th e steeri ng head. At th e sa me time , th e bi ke is extremely com pact and closecoupled, with th e wheelbase down to 54.8 inches from 56.8 in. three years ago in 'IT F I form, reduced to 55.6 in. la st season. Head angle is a steep 24.3 degrees and trail a m ere 3.92 in., the sort o f steering geometry yo u'd find o n Lawson 's a nd Rainey's GP 500s, which wou ld also have a forward weight bi as not so unlike th e Bimota 's present 54/ 46% - itself a ch an ge from Martini's origin al 50/ 60% layout on th e fir st YB4. So what we hav e is a four-strok e GP bike by a ny o the r n ame, a n impression re inforced b y t he beau tifull y- fa b r ic a te d twin -spar chassis, m a d e o f Anri co rda 100 ai rcraft alIoy, in which th e FZ750 engi ne is tilte d back in th e fra me so th at th e cyli nde rs lie a t an angle of 36° fro m ver tical, rather tha n the original FZ's 45° - a m ove aimed a t o btaini ng a shorter w hee lbase, ac hieved by reca sting a new magne si um sump to aiiow th e Bimotadevelop ed ex ha us t to sit' sn ugly un d er th e e ngi ne, a n d rece n tly co pied by Yamaha th em sel ves o n th e ' OWO I. T h a t impressi on is rein forced, at lea st o n Big Ears' sis ter, by th e sturdy Ohlins O UT (o u tside upper tube) fro nt fo rks, an d th e Marchesini 'w heels shod w it h th e sa me Mich el in rubber as used by th e b u lk o f th e field in 500cc GP raci ng. T he ma ssive 320mm Brern bo d iscs a nd fo u r-pot calipers complete th e picture, chassis-wise. But it's not till you twist the th rottle on th e Bimota Superbike th a t th is picture beco mes tru ly com p lete, because fro m having been a superfast p ussycat o f a hi ghl ytuned ro ad bike whe n I sa m p led it last th ree years ago, th e works YB4 has now become a m ach i ne th at is at least ' as h a rd to ride fast as a modern G P 500 , and probab ly even more so. To obtain competitive horsepower from the FZ750-based engine, (Con tinued to page 37) 11

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