Cycle News - Archive Issues - 1990's

s toc k Mill e. Tha t's main ly du e to a tr ick ed -out, short-stroke engine prod uced in conjunction with their Rot ax engine su pp lie rs - an engine that w ill on ly be used in this mod el. Given that yo u are n 't p e r m it te d to change the engine stro ke in Wor ld Superbike racing, Ap rilia w ill ha ve to homologa te a bik e all ove r again (com p lete with 150 o ff min imum run for a co m p a ny o f Ap rilia's size) . Tha t's focus for you. So while the stock 998cc vo lu me- produced eight-valve Mille with chain-drive n DO HC m ea sures 97 x 67.5 mm wi th its torquey long-stroke .arch itecture, co m pared to its 98 x 66 mm Duca ti/Suzuki /Honda V-twin ri val s, ta ilored more towards rea l wo rld roa d riding - its race-orientated SP sister will see Ap rilia go to the other extreme and p ro d uce a sho rt-s troke 100 x 63.4 mm 996cc engi ne that has been d eveloped in conju nc tio n with Coswor th in Brit ain. This one has a pot enti al appe tite for revs to deliver the p ow er up high - a necessa ry in gredi ent fo r winni ng W orld Superbike races. Thi s underscor es Aprilia's d et ermination to match the benefits of Ducati 's desmod ro mic positive va lve operatio n with th e ir valve-sp ring V-t wi n , b y br eakin g new ground in piston speeds fo r a larg e -ca p a city twi n -cyli n der mot orcycl e engine . Bu t th a t' s not a ll: Togeth er with the bigger bo re comes an increase in va lve sizes, using revis ed profiles and cam timing for the chaindriven d ouble ove rhead camshafts.p er cylinder. Inlets are now up from 36mm on the stock Mille to 40.7m m on the SP, and ex hausts from 32mm to 36.5mm, each with two springs and set at a flatte r included valve angle of 30 degrees; compa red to 32 degrees on the stocker, and with harder exhaust-valve seats. Although Goddard's works racer runs same-size titanium valves and connecting rods, these aren't yet included on the SP. Bu t, according to SP development engineer Pietro Piccini (an ex-Ferrari / Aba rth engineer who's been working for Apri lia for a yea r exclusively on th is short-s troke motor): th ey wi ll be available via the ran ge of customer race kits. Those kits will take you all the way up to a full -on replica of God da rd's works engine that Aprilia plans to offer to SP customers who want to go racing. The SP's Coswor th-d eveloped cylinder heads are quite differen t fro m th e stock RSVl000 design. The larger valves necessita te a single central sparkplug instead of two, p lus revised porti ng and a new s m aller combustion chamber whic h incorpora tes Cosworth's trademark five-a xis m ach in in g p ro cess to op timize turbulen ce and cylinde r fillin g, aided by inlet ports w hich for this purp ose are quite stra ig ht, but riot excessively so. However, th er e' s a lon ger ' in take len gth compared to the road bike, aimed at im provi ng torq ue on this s ho rte r-stro ke m o to r . Su rprisi ng ly, though , the Mille SP's Nippondenso EFt runs the sa me single injector and 51mm throttle bodies as on the RSVl 000, but the race kit Aprilia plans to offer will have much bi g g er ones. Godda rd's works su perbike curre ntly ru ns 60m m butter flies, and a twin-injector sys tem. The Mill e SP engine has san d -cas t crankcases rather than th e RSV1000' s di e -ca st o n es, a im ed at in crea sin g s tre ngth a nd rigi dity at th e cos t of a slight gain in weight. Ditt o for the cylind er design, which is a stiffer closed-deck format ra ther than the RSV's open deck. However, the dry-sump engine's bottom en d is th e same as on the s tock Mille (with lightweight stain less steel oil tank just forward of the engine, on the left, and an uprated lubricati on sys tem As is immedi ately apparent on a race track (above), the Mille is much more race-oriented than it s volumeproduced RSV sib li ng. Slightly res haped carbon-fiber bodywork and a lower front ride height (left) make it the most streamlined production moto rcycl e ever . Unfortunately, the performance of the Brembo front brake (bel ow) doesn't measure up to the stellar Ohlins for k. wi th a secon d return pump), an d has no p rovision for an extra ctable gearbox as on so me other su p er bi kes , Th is is for fear of reducing crankcase rigidity with th e vertically-split eng ine. Gear rati os a re th e sa me as th e long-stroke roa d bike, thou gh with a straight-cu tprimary, and race tearns will have to open the engin e to cha nge them. But Aprilia ' s patented PPC pneumat ic slipper clu tch (in fact d erived fro m the works Bimot a Supermono) from the RSVl 000 has nat- urally bee n retai nedr .and race kits will include provisio n for a p ow er shi fte r, says Piccini, as well as a d ry clu tch like the one on Goddard's works su perbike. Fo rged Wis eco pi s tons fitted to a ni trid ed cra nk d eliver 11.5:1 co m pres sion , up from the RSV's 10.8:1, and are sti ll a th ree-ring d esign - thou gh God dard 's wo rks racer uses two-ring ones: conce rn over pos sibl e oil blow-by preven ted these being ad opted on the street SP. And Aprilia has reta in ed the RSV's twin bala n ce s hafts on the SP, even thou gh the wo rks supe rbike does wit hou t the one moun ted on the rear cylinder, in pursuit of a little extra pow er at the expense of so me increased vibra tion. You d o n oti ce a fe w e xtra tingl es when yo u rev th e stree t SP Mille hard, but it's a comple tely accep table level of vibra tion, and probab ly comes as mu ch fro m th e bala nce factor chosen for the engi ne, as from any inherent imbalan ce of a 6O-degree V-twin. '" '" '" ~ ~ E G> Ci. G> en 23

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