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/127698
All this and 1000 rpm of overrev which, because of all the extra punch low down, you now hardly ever need to use, bu t has a little step in the delivery at around 11,000 rpm which was enough to make it pop a fourth-gear wheelie almost every lap on th e down hill st ra ight af te r th e Spoon Cu rve - eve n when a w imp like me has the thrott le wound wide ope n just as you hit the little di p in the track surface there, on the racing line . Phew! Yet the engine is so to rq uey, yo u can short-shift at 10,000 to stop it w heely ing out of Suzuka's pathetic chicane or the u phill hai rpin, so as to get a better drive, but wit ho ut losing mo mentum. Choosing th e correct rat ios fo r th e side-loading six-speed gearbox must be a far easier task than in the past, because t h e co mbi na tion of th e im proved midrange and the Big Bang power delivery make it almos t irrelevant what gea r you' re in for any given tum . There is just so much pu nch and the engine is so forgivin g. In fa ct, rid in g H onda ' s fours tro ke RC45 su p erb ike is much more dem andin g in terms of getting the right gear for the righ t tum to keep the engin e turning up high and on the cam - a 185bhp GP two-s troke that is actu ally more ridable than a top superbike is kind of a contrad iction in terms. Yet the NSR ha s n ' t sacrificed top s peed to ob tain thi s extra punch: The new airbox - now running sligh tly p ress u rized, h igher th an a tmos p he re h elpe d take ca re of th a t, so tha t th e Honda is still the fastes t 500 in the pack, w h ile the m ech anical a nd e le ctron ic improvements made to the eng ine du rin g th e season we re a be tt e d b y the water-i njectio n sys tem th at debuted in the final race of the year. This acts as a power boos ter at low to midrange rp m, ad d ing an extra 10 bhp between 8000 and 10,500 rpm, says Hattori, thanks to a head er pipe attached to each cylinder to w h ich the " rea l" exha ust p ipe is then clam ped. These head ers each contain a nozzle w h ich sq u ir ts water in to th e ex ha us t, coo ling the exhaus t gases and modi fying th e p ressu re wave withi n th e pipe, to give the same result as if the pipes were longer than they really are. This in tum makes the eng ine more supple in terms of power delivery at low rp m: "We use the system to fill in the power curve at any point we choo se to do so," says Hattori. "We can move the pow er around by altering the injection tim ing on the rpm sca le, the duration and eve n the quantity of water injected - everything is controlled by the com puter." j Wha t we have here then is an artifi~i a l means of optimizing exhaus t pipe shape and dimensions, recognized as the key to two-stroke performance tuning since the days of Walter Kaaden and his MZ racers back in the early 196Os. Water injection is not new, but it's taken Honda .to apply it to GP two-strokes, with the ad ded benefit t hat it also b ri ngs of redu ci n g th e a mo u n t of loss of the inc o ming charge th rough the exha ust ports, in tum imp roving fuel consumptio n and with the ad ded benefit th at it al so b rin gs of reducing exh aus t emissions. " Wa te r injec tio n is an idea likely to p rove immensely valuable in making the fwo- stroke engine more environmentally a cceptab le fo r s t ree t u se - especially wh en combined with fuel injection, su ch as Honda are also d evelopi ng on the NSR500, b ut which wasn 't raced this "season after Itoh used it in Malaysia. b "The performance lev el with EFI is only the same as carbu retors, not an y better yet," says Hattori. "But we real ize its importance for the future of the twos t roke e ng ine, which in production te rm s is ligh t, less costly to bu ild and easy to use, but has the problem of fuel cons umption and emissions. So we will keep on wo rking on it, b ecau se of th e wide r possible app lication in the future." So don't ever say two-stroke GP racing has no a pplication to rea l-world motorcycling. okay? Maybe Ho nda have a green color scheme all ready for when the PGM -Fl fuel injection makes a change break. Of course, there's no point improving the power delivery if you can't get it to the ground, and the mod ifications made to the chassis and suspension at the start of the season were aimed at doi ng just that. The chassis was altered sligh tly for ' 1994, with the engin e lifted an d moved backward in the fram e to improve balan ce, and es pecially traction, while the swingarm was redesigned for the same reason. But to go two steps forward you must some times first take one step back, and th at' s wha t Honda had ' to do after the first two races. With Dooh an strug gling to finish third in the opening race in Australia, and only winning the next GP in Ma laysia after drastically changing his rid ing style as well as the gearbox ratios to cope with a bike that wa s a real handful to rid e hard, HRC were willin g to take the s tep b ack. Even that trick d idn't work well enough to stop Kevin Schwantz winning o n HRC h ome ground at Suzuka. But after an intensive A &3 a ~ test session at Jerez, the NSR' s Showa suspension was revamped to 1992 gu ise, and Doohan too went back to '92 mode and won the next six races in a row. "We made some changes to the forks and rear suspe ns io n over the winter which were not correct, " admits Hattori. "Because they were not compatible with the new tires Michelin produced for this (Top and middle) Naked Gunthe Honda NSR500 dressed down to its birthday suit. (Above) Alan Cathcart was fortunate eno ugh to ride Michael Doohan's Honda at the Suzuka Circuit in Japan . Cathcart calls Doohan's NSR the best motorcy cle he's ever ridden. 45