Cycle News - Archive Issues - 1990's

WORKBENCH By Nate Rau ba Gasoline - don't knock it I was hoping you could talk about gaso line - high-octan e race fuels, motorcycles required to use leaded fuel, keeping water (from condensation ) ou t of storage ca ns, or is condensa tion a rare problem? What is octa ne and can it easily be checked to prove an ad vertiser's honesty? Mike GrieH Coa l City, IL he average rid er, or race r, often co n te m p la tes u sin g hi ghoc ta ne racing ga soline rather than th e fuel readil y available at the local gas station. And o ften th e decision over wh ether or not to run race gas is furth er complicat ed by a co m m o n misconception th at high-octane fuel will deliver more . power and performance. High-octane gas will not give an engi ne more power. However, according to Trick Racing Gasoline, it will allow an engine to opera te at peak performance to gen erate th e extra power for which it was designed. T Inbellev KTM offers a Winning Deal to celebrate Mike Healey's125cc,250cc, and 500cc Pro Class SeriesSweep at the CMC Golden State ationals! While the 1990 KTMs are outstanding in their own right, Healey's winning bikes did have some slight modifications. Now, for a limited time only, you can buy 1990 KTM 250Cc and 50OCc.MX bikes with performance tuning kits that bring them up to Healey's record-breaking standards. These kits include: ~ ~ ~ _ 1iiI _ . _ , . - .A. Pro-Circuit exhaust pipe .A. Fork tuning kit ~IIKE HEAlEY ~IIKE HEAlEY ~IKE HEAlEY .A. Carburetor tuning kit .A. Up-to-the-minute technical and performance set-up Information .. Mike Healey T-shirt and decal kit This optional kit is available with every 1990 250Cc and 500Cc MX foran unbelievable price of $199.00 (more than 50% off their suggested retail price!) So race down to your dealer now. You bener believe that anoffer this good can't last forever. Built Ii)/' ClJampk)/78 KTMAMERICA, INC. east: 1906 Broadway, lorain. Ohio 44052 (216) 246-1060 West: 930 Fesler Stree t, EICajon. CA92020 (619) 256-0300 "You lose power because of detonation. Power is gained due to the engine not detonating.I! An engine ca n' t opera te at peak performance if it is detonating. Power is lost due to detonati on, th e hi gh-pitch ed ping or knock produced by abnorm al co m bus tio n or sponta neous co m b us tio n before ; th e spark plug fires. Detonation not o nly rob s a n engine of power , but severe cases may lea d to uncontrolled prei gnition whi ch ca n ca use burnt piston cro wns a nd othe r engine damage. " Yo u lo se power because o f detonati on ," sa ys Paul Thed e, fou nder o f Race Tech, a hi ghpe rforma nce a fterma r ke t ra ce shop. " Power is ga ined due to th e engine not detonating." Detonat ion ca n be caused by o ne or a co mbina tio n o f severa l th in gs, a cco rd i ng to Da eco G asoline' s ex perts. The fu el , co m p ress io n ratio a nd 'the ig n ition tim in g are th e maj or factors. We've said th at rac ing gas is a high oc tane fuel , but j us t wh at is oc tane? Octane is actua lly an oily para ffi n h ydrocarbon which is fou nd in pe tro leu m. A measu rement o f th e percen ta ge o f isoocta ne in heptane, another fuel , is th e oc tane number .used to ra te th e a nti-de to na tio n quality o f ga s. . The Am erican Standard o f T estin g Material establishes th e guidelin es by which tests a re co nd uc ted to determine the oc tane number o f a gra de of ga soline. A si ng le.cylinder laboratory engine with a variable co m p ression ratio is used in th e testing. The fuel being tested is fed in to th e engine a nd .th e co mpressio n ra tio is in creased as the spa rk lead is decreased until th e engine begins to detonat e. Then a m ixtu re o f the heptan e, w hich detonat es very. eas ily, and isooctane, wh ich resists detonation a nd is giv en an octane number of 100, is fed into th e engine a t the sa me com p ression ratio that th e test fuel detonated. The octane number is th en determined by th e pe rcentage o f isooctane in the heptane/isooctane mixture required to produce detonation under the sa me conditions as th e test fuel. There ar e two ways this test is carried o ut to reac h two different oc tane numbers. One test is don e with th e engi ne under a co nsta nt lo ad a n d th at d etermin es th e Research O ctan e N u m be r (R ), while th e other is carr ied ou t under a varying loa d , suc h as under racing co ndi tions , to determine th e Motor Octane Number (M). The yellow stickers yo u see on the pumps at gas stations giv e th e average octane number o f th ese measurements, thus the (R + M)/ 2 equation seen on those stickers. Since the o ctane number is limited to 100 with a 100% mixture of isooctane, tetraethyl lead can be added to further in crea se a fuel 's resistance to detonate and rais e the oc ta ne rating a bo ve 100. So how do you determine if you need to purch ase racing gas? "Use on ly as m uch oc ta ne as you need , it o nly co ntrols detonat ion," says Thede of Race Tech . " If it does n 't detona te o n pump gas , use th at . Wh en you start increasing co mpression and engine temperatu re, th en you may need rac ing gas." And accordi ng to Don Emler o f FMF, so me mach in es (particu larly large-bore two-strokes) just wo n' t quit detonatin g unl ess racing fue l is used. But racing gas is expe nsive since it costs more to p roduce. T ri ck recommends th a t ·if you r engine isn 't highly modified and doesn 't ' require a ll of th e oc ta ne that racing gaso line o ffers, try a mixture of race gas and unl ead ed premium street gasoline. With a little expe rime ntati on yo u ca n find th e right proportions to meet you r engine's oc ta ne requirem ent. " Use onlyas much octane as you need, it only controls detonation." If you mix gas a nd oi l for your two-stroke, you should kn ow th at a richer o il mixture has less oc ta ne: Oil doesn 't co ntai n octane a nd degrad es th e octane present in th e fuel. Yes, co nde nsa tio n in gas stora ge cans can occ ur. Water mixed with gas ca n be especially deadl y to twostroke engines since th e water ca n ca use th e oil to separa te fro m th e gas and fall to th e bottom of th e ca n. Four-strokes ca n to lerate a li tt le m ore water i n th e g as , a lt ho ug h wat er a lso d eg rad es oc ta ne. Wh en storing gasoli ne, Thede recommends th at th e co ntainer be sealed tightl y. Not o n ly does th at keep h ydrocarb on va pors from polluting th e a ir, but it also helps to prevent wa ter vapor fro m forming in th e can.

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