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Thread: Fuel

  1. #11
    Quote Originally Posted by Scrapeit View Post
    I think you'll find that motorcycles manufactured in Japan from sometime in the 70's will all be made to run on unleaded fuel, I use 91 and don't have a problem, my compression is approx 10.5 to 1 (stock is 9.5 to 1).

    I find 98 a waste of money.
    From about 1971/2 from my memory, it would have been due to the Japanese introduction of ULP and I'm sure their own standards of behaviour wouldn't let them market inferior quality internals for engines in holdout leaded fuel countries. It led to some terribly awkward marketing by the mid-80s when so many car models had to be stuffed about for the Aussie market.
    Somehow I also have a hunch that fuel we use now may be far more honest than the brews we used many years ago, much as the power figures makers could claim became honest sometime during the 1980s instead of the wildly exaggerated numbers that many makers used, I find my wheels (4 these days as I'm married and past it until I get another youthful spurt) happily run on 91 ULP with a 10:1 compression ratio, something that couldn't have been done 40 years ago, hell I had an slant 6 Valiant that pinged its head off even running super if I sunk the boot, a process that didn't otherwise achieve much more than create noise and pour raw fuel out the exhaust, Doubtless it could have been tuned vastly better but I was young and clueless.

  2. #12
    Lots of correct info here. Valve seat erosion was the 'issue' of ULP back in the day and Suzuki Valve seats were always hard enough and aren't effected by ULP. The octane rating of fuel doesn't tell you how much power per gram the fuel has; the power available per gram is the amount of heat released when that gram is burnt. It is quite possible for lower octane fuel to release slightly more heat than the 'good stuff', so of itself 98 possibly doesn't offer any power advantage per gram over lower octanes. In fact diesel oil yields more heat per gram than any octane petrol -it just burns too slow to make more horsepower than petrol.

    High octane allows dynamic higher compression ratio before detonation. (Static CR = the mathematical ratio, dynamic CR = actual and variable -affected by rpm, load, cam profiles/timing, exhaust design, inlet tract length, supercharging, ignition timing, temperature... etc). An engine designed (or modified) to make use the extra head-room before detonation of high octane can turn more of the heat in the fuel into pressure within the cylinder and torque at the crank. Modern engines often rely on multi sensor engine management and fuel injection to achieve the most efficient burn for the load/rpm and fuel used. Short story is anything unmodified and using carburetors will not benefit from higher octane than specified by the manufacturer.
    Last edited by Kiwialfa; 25-02-19 at 09:36 AM.
    Darryl in E27-land


  3. #13
    Quote Originally Posted by Kiwialfa View Post
    diesel oil yields more heat per gram than any octane petrol
    I think Diesel is very similar to other hydrocarbons in respect of energy content per gram, however diesel denser than other fuels so has a higher energy content by volume or the good sensible litres we buy it in, in fact it would be an excellent choice for jet aeroplanes except for the density issue, since the kerosene they prefer has static electricity issues that diesel doesn't have. But then again the USA controls things so they still overdose their piston engines with lead and use Fred Flintstone era "feet" as an altitude unit, while the rest of the world is too gutless to stand up to them and bring them up to date.

  4. #14
    Senior Member NSW
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    Am I the only one to get a chubby reading this technical discussion eeeek !!
    Last edited by GSX1100dreamn; 25-02-19 at 08:05 PM.

  5. #15
    I have a std 83 1100 and use 95 octane without any issues.
    Previous Rides - 1981 650 Katana, 1988 GPz750R
    Current Rides - 1981 650 Katana, 1982 650 Katana, 1983 650 Katana, 2 x 1984 750 Katana (Darkside), 1985 750 Katana (Darkside), 1983 1100 Katana
    Donor bike 1981 650 Katana

  6. #16
    You can use 98 with no issues but it costs more.

    91 burns faster but with 'low' compression no problems, 'high' compression motors may not like 91 and needs a slower burning fuel, my kat is not stock but runs 10's at Willowbank on 91... just sayin'

  7. #17
    Quote Originally Posted by Jimby View Post
    But then again the USA controls things so they still overdose their piston engines with lead and use Fred Flintstone era "feet" as an altitude unit, while the rest of the world is too gutless to stand up to them and bring them up to date.
    The lead in Avgas isn't primarily for valve seat protection.

  8. #18
    Yes, good old tetra-ethyl lead, magic for raising octane ratings while poisoning everyone. Invented by American scientist/inventor Thomas Midgley, who also single handedly destroyed the ozone layer with his other major invention Freon aka CFCs.... Died by accidentally strangled himself in the rope and pulley system he built to move his polio paralyzed body out of bed. Talk about shit luck.
    Darryl in E27-land


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