Cycle News - Archive Issues - 1990's

, -. does an "e ngi ne-ma nagement system" sou nd ? Th e ignito r box on the GSXR does jus t that - it manages. Controlling the ope ration of the igniti on, carbure tor th rottle slid es and the fuel pump, th e new sys tem takes input it receives from sensors monitoring engine rp m, throttle position and gear position and man ages it . Due to d ifferent operating tem peratu res between cylinders, the "black box" contains sepa rate ignition timing map s for cylinders one and fou r, and two and three. Each map is also d ivid ed into four ad ditional curves based on the degree of throttle opening . In th e end, all th ree senso rs help the box determine the best timi ng curve for a given rid in g si tuation. The sa me sensors also con trol lowspeed thr ottl e slide operation. GET SHORTY With the narrowe r cranksha ft des ign, Su zuki engi neers were able to relocate the s tar te r s yste m fr om behind the engine to the righ t si d e of th e cr ankshaft, adding some width to th e motor b ut taking away length, which allows for a shorter wheelbase - a simple tra deoff. The shorter crankcase is also possibl e because Suzuki stacked the crankshaft and transmission shafts in a trian gul ar pattern . The new crankcase is 15mm shorter tha n the '95 mod el' s, and this sys tem also allows the tra nsmiss ion shafts an d gears to be serviced wi tho u t d isturbing the crankshaft main bearings. All of this resulted in a lighter crank 1000 grams lighter to be exac t - while the new cylinder head is som e 1500 grams lighter. Suzuki also saved weight with more convention al means, using plated cylinders in ste ad of iron liners, simplifying coolant-hose routing, using magnesium engine covers, etc. To give the GSXR750 quick revving capability whil e boo sting durability and reliabili ty through lower piston speed, Su zu ki engi neers have given th e new engine an extremely short stro ke (72mm x 46mm as co m pa re d to 70m m x 48.7mm for last year's mod el). The higher-revving engine now has a red line of 13,SOOrpm. In ad ditio n to th e wei ght and size savi ngs that go along with th e use of plated cylinde rs, Su zuki cl aims they improve engi ne-cooling per forman ce. Each cylinder bore is plated with silicone-carbide embed de d in nickel, a feature that Su zuki claim s a lso redu ces I cylinder and piston ring wear. Because alu minu m has three times the heat dissipation of iron, Su zuki says a hi gher compression ratio can be used with the plated cylinde rs and also a tighter piston I cylinder clearan ce th at reduces piston slap, oil consumption and blow-by. Those pistons now feature flat tops and the includ ed valv e angle is o n ly 29 degrees, with 29mm intake valves and 24mm exhaus t valv es. The compression ratio o f the .n ew bike, h ow ev e r, is unchanged at 11.8:1. Th e latest GSXR also uses a bolt-on crank web, allowing the primary gear to be machined withou t reducing the size of the crank web. To beef up reli ab ility, Su zuki has bolted the transmission an d crankshaft s u rfaces in line w ith th e piston s a nd cylinders - ensuring that the bolt torque is in the same direction as the load bein g applied to the cran kcase, which in turn gives the case rigidity . Piston cooling has also been improved by putting the oil jets closer to the pistons and directing the spray pattern more accurately. Thanks to the e ngi ne lean of 25 d egrees, the d ownd raft 39mm Mikuni ca rbs (which now feature a tapered slide to aid fuel ato mization at slower engi ne speeds) are now p rovide d wi th a straighter sho t of mixtu re into the ports. Air is fed via the Suzu ki Ram Air Direct (SRAD) sys tem, whi ch ro utes tw o ch annel s of air fro m both side o f th e head li ghts - through the fr ame and into an airbox which sits under th e gas tank. In previous years, air intakes really only d irected a ir somewhere close to th e airbox. But the new GSXR gets much more th an new carburetor plac em ent. How Hard to believ e, ye t true - th e new GSXR750 ha s a shorter wheelbase than Kevin Schwantz' s 1993 RGV 500 . At 1400mm (55 inches), the new light er and s tiffe r chassi s is a wh opping 35m m sho rte r th an last yea r's GSXR750, and it' s that lack of leng th - combined with its skimpy we ight - that trul y mak es this bike feel more like a 600 than a 750. It's rare that a m od ern sportbike ac tually looks short, but this one does. Becau se the engine now sits with its cylinders tilted forward 25 d egrees, the steering head tube was thus m oved some 30mm cl o se r to the swinga rm pivot, and the swingarm itself has been shortene d b y 5mm . Shorter, yes - but a lso stronger. Su zu ki clai ms th a t th e ne w cas t-alu minum swi nga rm is no t only 400 grams lighter than last year's mod el. but also 12 percent more rigid . In ad d itio n, rac e-kit parts w ill allo w go fast purchasers to ra ise or lower the pi vot cen ter of th e sw inga rm by 2mm via inserts. Going along with the rest of Suzuki 's plans to build the lightest 750 on the planet, the chassis was ano ther area where engineers managed to shave off 15

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