Fuel Mixture Do I have to change my fuel ratio if I use 93 octane fuel??

Discussion in '2-Stroke Engines' started by StrontiumEthics, Aug 20, 2008.

  1. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    Do I have to change my fuel ratio if I use 93 octane fuel??

  2. Skyliner70cc

    Skyliner70cc Active Member

    No, but you should change your mind and use a lower octane fuel unless indicated otherwise.

    What is your reason for 93 octane?
  3. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    I thought since its better for cars then it might be better for my engine? Pretty ignorant of me I guess. So which should I use? Is the lower the octane the better? Fill me in please before my next tank, lol.
  4. Skyliner70cc

    Skyliner70cc Active Member

    You my friend, are a advertising executive's dream. No, higher octane is not better for an engine.

    Here is a little article that basically sums up my beliefs. http://www.wanderings.net/notebook/Main/IsHighOctaneGasWorthTheMoney

    Your best bet us to always use the lowest possible octane fuel that an engine can tolerate. High octane fuel is typically used in engines with high compression ratios, turbos/superchargers, or reccomended by engine manufacturer.
  5. Warner

    Warner Member

    True. Octane rating has to do with flame speed. High octane = slower flame speed. Running too high an octane in an engine that doesn't require it will yield LESS power and more heat (and likely higher emissions since the fuel doesn't burn completely).

  6. JemmaUK

    JemmaUK Guest

    The only reason 93 octane should need to be used is if you are running a car engine with anything over an 11:1 compression ratio. I.e. a competition or highly tuned motor.

    91 is more than enough for the happy times and to be honest they'd probably run on the old "pool petrol" that was often 10% gravel... or so my grandfather used to tell me.

    The general rule is - the higher the compression the better quality the fuel has to be. A modern 10.5:1 compression engine would probably run on bad quality fuel given that it has computer control - the MPG and performance would be bad and cue the hitherto unknown noises from the motor.

    The happy time engines are about at the stage car engines were in the 1930s-40s. they share, or slightly exceed the compression ratio of the Rolls-Royce merlin. Its no coincidence that a power output of 1000hp then needed 27 litres - nowadays we can manage it in 8 litres (although to be fair you seldom saw a Merlin with 4 turbochargers, 10 radiators and a VW badge).

    In conclusion, any petrol that you are able to get hold of, the HT engines will run on - they are so low compression that it really makes little difference and you are just spending money you dont need to spend.