Cycle News - Archive Issues - 2000's

SUZUKI GSV-R ENGINE TECH: Why and Wherefore? Seen on its own during an engine change by the tes t team in preparat ion for my ride (no photos allowed - pity!), the GSVR Suzuki's XRE2 65-degree V4 16-valveengine is very narro w and compact, with a very small, narro w, knife-edged 2003, this had the same shorter stroke as today 's bike has, for more revs and less torque. Suzuki also once had the compress ion ratio very high, at around 15.5: I on the XREO, which was a further factor in instability under acceleration cylinders, w hile that for the front pair is longer but wider in diameter - a bolde r version of the same concept used on Ducati V-twin superbikes. "We must fit the twin-pipe system for the XRE2, because sump that minimizes oil surg in any direction and is effece and under engine braking . Now it' s a point or more lower, tively an oil tank parked beneath a dry-sump moto r in the best I960s MVAgusta/Bene llifashion. The cylinder heads and blocks, which each contain a pair of inevitably quite meaty pistons for the high-revving shortstroke moto r, are each hardly any bigger than a 450cc MXlenduro single's. There's a single 360-degree, plainbearing crankshaft with paired crankpins, gear drive to the four overhead camshafts, titanium conrods and valves (the latter with bucket-and-shim adjustment and a very flat included angle - as evidenced by how close the tw in overhead camshafts are set to each other), and forged pisto ns and the bike is more controllab le, with a smoother delivery of power peaking at 14,200 rpm and the rev limiter now set at 15,300 rpm - 1000 revs higher than two years ago. Yes, but how about power? Has that ke pt pace with the improvements in rideab ility, compared to the over "2 10 bhp" at 14,000 rpm the XREO delivered two years ago? "Now, not so much more!" Arase-san says. "Maybe we have 10 ps [hpj more than in 2002, but now we know we need more power to improve throttle controllability, as well as to keep up with other machines. We have improved many other factors . Now only top speed re mains a big problem." The GSV-R's fuel injection system employs a Mitsubishi ECU matched to four separate throttle bodies of undisclosed bore , which are now Mikunis rather than the Kei hins used previously on the XREO, since these are better adapted to the ride-by-wire system intr oduced for 2003. They're also now smaller in diameter than a year ago - to help achieve a be tter spread of power, even if it inevitably means some sacrifice at to p e nd - and are positioned centrally in the middle of the V. with two injectors pe r cylinder. One of these is mounted below the throttle butterfly, the other above it but off to one side, almost parallel to the lower injector rather than directly above the intake trumpet, as on some other F1derive d systems , placed here mainly to avoid making the narrow-angle engine package any taller. Suzuki has also experimented w ith different length trum pets - longer for more torque, shorter for outright power and more top end - while the differential -diameter 2-2- 1 Yoshimura titanium exhaust system with oval-section headers replaces the 4-2-1 system used previously. This has a shorter, narrower-sect ion pipe on one side serving the rear bank of w ith this firing order we cannot converge exhausts," Arase san explains. 'Al so, we use megaphones to increase midrange w ith just two rings each to reduce friction w ithout creating oil blow-by problems. To minim ize vibration from the narrow-angle motor, there's a single, gear-driven balance shaft mounted between the cylinder banks which also drives the water pum p on the left and, since it is not positioned between the cranksha ft and clutch, means the engine rotates forward in the conventional manner (not backward , like the YamahaMI). Dry weight is a reflect ion of the e ngine's compact build, with the original XREOweighing right on the then fourcylinder weight limitof 145 kg (3 19 pounds); after this was since raised three kilos, the current XRE2 scales in right on 150 kg (330 pounds) with oil and water but no fue l. In spite of its greater appetite for revs than before, Suzuki's engine designer and R&D boss, KunioArase, insists the XRE2 moto r does n't have too exaggerated an ultra shortstroke format . The first 60-degree XREO engine had a longer-stro ke design, leading to excess ive bottom-e nd to rque - and thus too many wheel ies - plus a reluctance to rev out . But w hen Suzuki developed the 65-degree XREI for level, exactl y the same sce nario pe rtai ns w ith th e Suzu ki GSV-R. Suzuki has create d a ve ry small, slim, lighthan d ling bike by MotoGP sta ndards, whi ch ta kes full advantage of the co mp act mass de livered by that narrow-a ngle V4 engine and has a really balanced feel, wit h re duced we ight transfer that makes it a great ride for a twi sty track like Vale ncia - but probably on ly w hen yo u're riding alone, as I was on Suzuki's private t est day. Th en , yo u can build up confid enc e in the bike a nd w ith t he fro nt tire to the po int that you can even take some co rners o ne ge ar highe r than yo u started ou t do ing, maximizing turn speed to sta rt cutti ng halfway dece nt lap times on a bike that's come a long way in two years in terms of handling and user friend liness - or maybe just four months, to be strictly hon est , since the crucial debut at Catalunya o f th e X RE2 motor w ith its revised, more usable firing orde r. But - and here 's th e big problem - as Loris Reggiani discover ed time and again 10 years ago w hen he raced the 400 cc Aprilia V-twin against the more powerful, less agile V4 500cc bikes : You can cut fro nt- ro w times in qualifying if yo u loo k hard enough for a clear t rack and can may be grab a crucial tow at the right moment on the run to the line , but trying to do the same thing in a race, with faste r bike s zapping past you down the straight then parking themselves in the turns and inviting you to hit them up t he rear or back off the gas to avoid doing so , o nly for them to use thei r superior acceleration to leave you standing on the way out of the corner, is an impo ssible dream. Kenny Roberts discove red that again at Rio this year. torque in order to improve rideability and help smooth out power delivery." They sound good , too . The Suzuki's unmistakably gruff exhaust note sounds like nothing else on the MotoGP grid, rippling with muscular menace and exuding a prom ise of power wh ich it may well soon live up to if Suzuki's hardworking engineers have their way. Suzuki's original 1000 km (620 miles) engine rotation time for servicing back at the factory has now been cut in half with the higher-revving motor, says Arase-san, when the valves, pistons and conrods are up for rep lacement, though crankshafts last up to 1200 miles before they must be replaced. The six-speed cassette transm ission is of course fully extractable, with a very compact, multiplate, dry ramp-type slipper clutch, which is self-compensating, slipping progressively only when reverse loads are high and re-engaging smoothly. According to Arase-san, from the start of the project , the GSV has only ever had electronic thr ottle control, -R not Yamaha-type valve-lifters to aid decom pre ssion under engine braking. This system has been considerab ly improved since two years ago, but Arase-san insists it has neve r bee n complemented by tracti on co ntro l. "We never had a wheelspin control system like this," he says. "O nly we make the engine torque more smooth and throttle controllability better, so the rider can cont rol a wheelie more easily himself - especiallymuch better than two years ago with XREO. This is our only cont rol system:' If this is the case, all the more kudos to KRfor that lightninggetaway from pole position at Rio, then. This is the GSV-R Suzuki's big hang -up right now, and as someone wh o' s been there, done that in a much more humble class of rac ing (but for exactly th e same reas o ns and with comparab le t ires w it h the same attributes as wh at it' s running), my symp athy goes out to Kenny a nd John, and I join them in w ishing Suzuki's engineers a fair wind in finding that missing horsepower. Because, wh e n (if?- no, these are the guys that first made 200 bhp super bikes!) its engineers find it, t he GSV-R Suzuki w ill be one swee t package to ride to victory. It has the rest of the package , so all that's missing now is the ex tra horsepower. And after being shown KTM's compute r simulatio ns w hich determined that a 75-degree include d cylinder angle was the minimu m t hat could be employed to allow the LCa V-twin and MotoGP V4 en gines bre ath e w ell enough to deliver competitive horse power in t heir respective classes I'm betting that Suzuki is go ing to have to follow suit and wide n the angle of its own MotoGP co ntender to a similar ex ten t in orde r to sta nd a cha nce of finding that missing ho rse powe r. Th ough it's certainly mo re po ten t t ha n t he bike I ro de a year ago a nd has much be tt e r power de livery a nd en gine bra king , th e 2004 GSV-R still feels slightly strangulated at higher revs , which in turn impacts on acceleration and top sp eed . Suzuki engineers won't confirm they're working on a wider-angle V4 for 2005, but I'm betting they'll have to - in which case the challe nge will be to find the e xtra horsepower they're lacking at pres e nt . wi thout sacri ficing the sweet- han dling, rideable package they have at present. Hey, nobocly said it was going to be easy! CN www.cy clenews.com CYCLE NEWS . DECEMBER 1,2004 27

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