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/126808
New TSCC TSCC Swirl Exhaust Valve +l'Pr-- Diameter/ 18mm %11"'-';' ;~~;;;I)~t=:::New TSCC Profile :j..;"=~~~"", Sq uish Area Spa rkp lug Hole Diameter/ 10mm Cylinder Bore Profile Intake Valve Diameter/ 21mm (A bove) Diagram compares old TSCC (left) with new, more compact version with large valves . (Below) The oil-coo ling system; 21 quarts of oil per minute are pumped into the camshaft/valve-t rain cavity . t (Above) New TSCC design lies totally w ithin the cylinder bore , (Below left) Idler gear between cam chain sprockets eliminates cam timing changes. (Below right) Exploded view of the dual-piston brake caliper . 12 (Suzuki engine ers have detailed and persuasive arguments that four va lves per cy linde r provide optimum efficienc y. Th e co m p an y went so far as to provide the press with char ts co m paring effective intake por t area with valve lift volum e and demonstratin g th eir co n victio n th at five-valve a nd six-valve lay outs do n ot in crease efficienc y a nd add ne edless co m p lexi ty. Regular read ers will recall th at Yam aha eng ineers recentl y adva nce d th eir reasoning th at the FZ750's five-valv esper- cylinder layout was th e key to high h orsepow er a nd effi cien cy. Th e o n ly wa y to resolve the issu e will no doubt be to co m pa re th e performan ce of th e two machines side-by-side wh en th ey're both a va ila ble in th e U.S.) The ca m sha fts are driven by a roll er cha in o ff th e center o f th e cra nksha ft; guide sh oes are positi oned in front of th e cha in's forward run and behind the cha i n 's rearward run , with an automatic tension er system. That much is co n ventio na l Suzuki practi ce. Bu t th ere's an idler sprocket, mentioned earlier, positioned in th e cyli nd er h ead between th e ca m sprockets. That extra sprocket is a standard Suzuki ra ccbike trick, and prevents a standing wav e from developing between the sprockets - al lowing ca m timing to chan ge wh en th e throttl e is ba ck ed o ff a t high rpm , Va lve a ngle staye d th e same a t 2 10 (i n cl u de d) , but compared to th e GS7 50, GSXR 750 valve stem sizes were reduced fro m 5.5m m to 5.0m m to reduce restricti on in th e pons. Th e ports th emselves are as stra ig h t as possible; a nd th e intak es run down ward to th e valves. a nd reduce in di a meter, then spl it in to two cha n ne ls just before th e va lve g u ides, o m, cha nnel leadin g to eac h va lve. T he intak e pons aim in ward to a llow close-set ca rbure to rs a nd ma ximum rider kn ee roo m; th at 's sta nda rd in li ne- fo u r practi ce. Th e ca rburetors o n th e GS X R i50 are 29 m m flat- sli de Mi kun is wi th power-jets; th e power-jet ci rc u i ts feed gas d irectl y from th e float bow ls in to the ca rbureto r th roa ts a t hi gh rpm , su bsta n tia l l y bo o st in g h igh -rpm power. In th eo rv, flat-slide car bure tors have li ghter slid es, better response wh en th e th rottle is o pe ned a fter deceleration (as wh en accele ra ti ng o u t of a co rner) , a nd are shorter, a llowi ng a m o re co m pac t layout. ' T he p arti cul ar ca r bs o n th e G SXR750 ar c fed by a large volume airbox assem bly (8.5 qt. vs. the GS7 50's 5.8 qt. j with th e air clean er positioned a bo ve th e ca rbureto r intak es, under neath the hollowed -out rear of th e gas tank . The exha ust syst em is a four-in toon e with a bl ack heat-resistant coat ing; th e exha us t flows more air th an most stock mot or cycl e exha u st system s, has a raci er so u n d , a n d weigh s 39% less than th e co n vent io na l fourinto-tw o svstern o n th e GS 750. Prim ary d rive is stra ig ht-cu t gear; ma chined direcrl v into o ne of the cra n kshaft flyw heels: the circu m ference of the flywh eel is h eat- treated after the gea r teet h are machin ed into it. The straig h t-cu t gea rs offer less th eo retical m echani cal loss than helica l gears used for th e G S750 's prim a rv drive. T he cl u tch, d riv en direct lv hv th e cra n k gear a nd locat ed o n th e rigtu side o f the engi ne, is co nve nt iona l multi -p la te, runn in g in engine oi l. ft is h ydraulicall y ac tiva ted , th e sla ve cy linde r po siti oned o n th e left side o f th e engine ; a rod throu gh th e tran smission main sha ft p us hes th e cl u tch pressu re p la te, Cl u tch springs are coil type, n ot th e li ghter-tou ch di ap hragrn type seen o n man y h ydra ul iccl utc h-e q u ipped mach ines. T he a lte rna tor is gea r-d riven o ff th e clutch a nd is positioned behind the cyli nde rs on th e right side of th e engi ne, a bo ve th e clutch. With th e a l terna to r o ff th e cra n k, eng in e width can be reduced and, because th e cra n k. sha ft assem bly is lighter , th rott le response improves; peak sa fe rp m is a Iso in creased . Th e electro n ic ignition is triggered o ff th e left en d o f th ecrank . underneath a tapered co ver. All th is engine techno logy is packed into a lightweight a l u m in u m fram e, a nd it 's th e fram e that th e Suzuki engi ne ers a re m ost proud of. Manu facturi ng a luminum fram es is more difficult th an manufa clUrin g stee l fra mes, a nd th e engineers say th ey co st 2.5 tim es more to buil d. Suzu ki' s fra me for th e G SXR 750 is a co mbi na tio n of lo w- p ressu re ca stings and extruded t ubi ng; th e ext rusion s a re roughl y square . in cross - sectio n, hut are th icken ed in the corn ers - in cross-section, it loo ks like th er e's a bead o f extra a lu m in u m protruding from eac h co rner. From the sid e, i t looks like th e center of th e tube is in dented from th e edges. T ha t tube co ns truct io n effectively ma kes th e walls thicker a t th e edges, which tak e th e most stress, a nd th inner in between the edges, in areas th at don' t tak e as much stress . The result is a rigid tube with li ghter weight th an the eq uivalent-stre n g th tubing with un iform wall thickness a nd flat sides . Beyond th at , th e en tire frame structure is si m p le in design a nd exec u tion. It ' s mad e of 26 indi vid ua l p ans , co m pa red to 96 individual p ans us ed in the co ns tr uc tio n of th e steel GS750 fram e, a nd it weighs 17.9 pounds co m pa red to th e GS7 50 frame's 37.5 pounds (a ll figures not incl udi n g the swin ga rm) . Th e rectangular- section sw ingarm o n th e GSX R750 weighs 5.7 pounds vs. th e GS750 sw in gar m' s 7.1 pounds. According to th e Suzuki en gineers, th eir cho ice o f exact a l um in u m a ll o y material s (incl udin g more zin c, silicon and iron ), propri etary welding process a nd casting ex pe rt ise gives th e GSXR750 a frame th at will withsta nd 10%defl ection wi thout crac king or breakin g, co m pa red to 5% maximum defl ect ion fonnd in a seri es of tests th e co m pa ny perf ormed o n a H onda NS250 frame. Th ey're also quick to poi nt o u t th a t an NS2 50 fra me weigh s about 3.0 pounds mo re than a GSXRi50 frame.