Cycle News - Archive Issues - 1980's

• The internals of the GSXR motor. Every part was designed to save weight; the biggest savings are in pistons and rods. nals; set of fo ur co n nec ting rods. 0.8 pou nds ; set of two ca ms hafts (the GSXR 's ar e holl ow ), 1.5 pou nds; pistons, 0.74 o u nces eac h. The weigh t sav ings a re even more impressive when loo ked at in terms of percentages; Cra n ksha ft, 19%lighter; co n nec ting rods, 25%; pi stons, II %; cyli n der h ead , 22%; cylinde r, 17%; valve cove r, 39%. (Co mputer stress a na lysis co n tribut ed to wei ght reduct ions made in parts lik e co n nec ting ro ds . wrist pi ns and pistons ; th e a na lysis made it pos sible to bu ild those parts to th e st reng th n eeded wi thout weigh tadding overbui lding.) The eng inee rs went beyond that. The cra n k a nd ca m sp ro cke ts for the cam cha in were reduced in size, th e cra nk ge tt ing 15 teeth (ins tead o f 17) and th e cam sprocke ts eac h ge tt ing 30 teeth (in stead of 34). That ch ange a lso allowed use o f a shorter (a nd ligh ter) ca m cha in , alt hough th e total loss there was probab ly gained back a nd then so me by th e addition of a sprocket ro ller in th e cylinder head , between th e ca m sprockets. (more on th at la ter). An d th ere's no dou bt th at th e large oil cooler is hea vier th an th e GS750's sma lle r o il cooler. Bu t ove ra ll , even th ou gh th e co m p a ra ti ve e ng i ne weights li sted ea rlier (161 pounds vs. 176 pou nds) don ' t incl ude oil co olers, th ere's no doubt tha t th e weight loss mad e p ossible by th e new coo lin g system far , far exceeds any weigh t ga in from system parts suc h as th e coo ler and th e dual oil pump. The othe r as pec t o f en gine development mad e possibl e by th e cooling system has to do with horsepower outpu t. The bett er coolin g mad e more power poss ib le, but th a t power had to co me fro m somew he re. Since th ey were starti ng with a clea n p iece o f paper for th e GSX R 750 engine , th e engi nee rs took a hard look a t Suzuki' s T win Swirl Combu stio n Ch amber (TSCC) , a fourvalves-per-cylinde r la yout tha t has given th e co m p any good service since its introd uc tio n with th e GS I IOO in 1980. T he system basicall y uses a com bustion cham ber sp li t do wn th e midd le (fro n t-ro-back) by a ridg e between th e sets o f intake and ex ha ust valves; half -hemispheri cal shapes on each side o f th e ridge di rect th e in co ming fu el /air mixture into a forwa rd and-down swirl pattern tha t promot es good cylin de r cha rg ing a nd a more homogenous m ixture through out th e cylinder. But th e co m bus tion chamber edgcs over la p ped th e cyli nde r bore, a nd a lt hough th e system proved bett er than o ther Iour-valves-per-cylinder designs in use a t th e time o f its introducti on, it wasn 't as effic ien t as it co u ld be. Some racebike tu ners seeking more p ower cu t chamfers into th e top o f the cylinder - locat ed a t the four corn ers of the co m bu stion cha m ber - th ink ing th at woul d improve flame propaga tion a nd discourage de to na tion . For the GS XR , th e en ginee rs develope d a more co m pact T SCC, with la rger valv es co m pared to th e GS750's valves (26m m vs. 25mm in takes, 24mm vs. 21mm exha us ts) and a h ig her co mpression ratio ( 11:1 vs. 9.6:1). T he new TSCC layo ut does n ot ove rla p th e cylin der bores. The GSX R750 's bo re a nd stro ke o f 70x 48.7m m (com pa red to th e GS750' s 67 x 53 m m) ha s a lot to do wit h the' redesign of th e TSCC as outlin ed a bove- - th e - rel a tivel y Ia rg e bo re. ' especia lly in relationship to th e stro ke. mad e it possibl e to increase valve size, ra ise compression a n d pu ll th e edges of the co m bus tio n cha m ber in wit h in th e cylin der bo re. Valve tim ing for th e G SXR750 ha s th e in ta kes o pen ing 38° BTDC a nd clos ing 66° ABDC; th e exh a us ts o pe n 63° BBDC a nd close 37° ATDC, m easu red to a nd fro m 0.3mm lift. Int a ke va lve lift is 8.2m m, ex ha us t va lve lift 7.5m m. (G S750 intak e valv e tim in g is 38-62° w it h 8.2mm lift ; ex ha ust valve ti mi ng is 66-26° wi th 7.0m m lift). GSXR750 Suzuki Engine type A ir-cooled DOHC in line -four Bore x stroke 70x48.7mm D isplacement . • .. . . ..•• 749cc Compression ratio •• . . . . . 1 1 : 1 Carburetion . . (4 ) 29mm Mikuni fl at-sli de Ho rsepower . . . . . . . . 104.5 bhp @ 10.500 rpm Torque : ... . •. .. . . . .. 52 lb .-ft. @ 9 0 0 0rpm 4 Valves pe r cy lind er Intake valve size . • . . ... . 26m m Exh au st valve size .• ••• . . 24m m _ 8 .2mm Intake lift Exha ust lift • • . .. . . .. . . 7.5mm 21° Inclu ded valve ang le Intake va lve t im ing ~ . 38-66° Exhaust valve t iming 63-37° (m easuring pt .) • • •• •• • • 0 .3mm Ignition Electronic Lubrication . .. . . ..• . . Wet sump Redline . • • • • . .. .. . 11 .000 rpm 4500 rpm rpm @ 60 mph Gear ratios Primary • • • • • .. 75 /43; 1.744: 1 Final . .. . •.. . . 42 /14; 3 .000:1 6th 23/21 ; 1.0 9 5 : 1 5th 27/22; 1 .227:1 4th . • • • •• •.. 28/20; 1.400:1 3rd .. ...• . • • 28/17; 1.647:1 2nd • • . • • • • • 33/16; 2.062:1 1st • • • • •• •.. 36/13; 2.769:1 Calculated speed in gears at redline 6th 147 mph I I I" .. l • c, .. 5th •.. . . . • • • • • . . .. . 131 mph 4th • . . . ..• • •. . . • • • •115 mph 3rd 98 mph 2nd • . . . .. . . ... .. . .• 78 mph 1st .. . •• .. ..• • • . ... • 58 mph Frame . .. . .• • ... Double -cradle. retangula r alumin um-alloy tubing Rake . . . .•... •• •• •• ...... 26° Trai l. . . . . . . . . . . . . . . • . • . 4 .2 in . Fro nt su spen sion .. . Telescopic forks Fork tube diameter . . . • • • 4 1 mm Front wheel travel • • . .. .. 5 .1 in . Rear suspension • • Sing le-s hock swingarm Rear wheel t ravel 4 .7 in . Front brakes . . . (2 ) 11 .8 -in . disc Rear brake • . . . . . . . . 8 .7 -in. di sc Fro nt w hee l • . .. Cast aluminu m 2 .50x18 in. Rear wheels •... Cast alumin um 3 .50x18 in . Front tire . .. .... .. 110/80-18 Bridgestone Excedra G527 Rear tires . • • . .• • • • 140/70-18 Bridgestone Excedra G528 Dry weight. • • . .. . . . . • 388 Ibs. Wheelbase . • • • ..•.• ••• 56.5 in . Fuel capacity .. • • . .... . 5.0 ga l . Ground clearance . .. . . _. 4 .7 in . Seat height ...•• ••••. . . 30 in . GVWR .. • •• • •..• ••• •. • • N/A Colors . .. Blue/white. red /black Retail price N /A 11

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