Fuel Mixture What octane rating do you use?

Discussion in '2-Stroke Engines' started by 2strokepoke, Aug 22, 2011.

  1. 2strokepoke

    2strokepoke Member

    My friend uses 89 because he fears using 93 would put too much stress on the lil HT. I know with real mopeds ( Puch,Peugot etc..) you can push the limit a lil more by using 93 and octane booster but I'm still not sure if you could get away with that on a HT.

    What do you run?

  2. steelfan41

    steelfan41 Member

    93 octane @ 32:1.
  3. HeadSmess

    HeadSmess Well-Known Member

    i love how everyone who doesnt know what the %^$^ theyre talking about has this misconception that hi octane numbers equal more power :rolleyes7:

    is the engine built to require hi octane? like, a 13:1 compression ratio? running at 12000rpm? octane is a rating for anti-detonation characteristics. not power rating. detonation is a fast explosion. low octane fuel detonates with high compression ratios. because low octane fuel burns rapidly.breaks apart easily. hi octane fuel burns slowly. therefore it doesnt tend to "explode" as much.

    at normal 8-9:1 comp ratios, low octane fuel delivers more power as it tends to "combust" more completely than the "hi octane" thats still only half burnt...

    this all changes when you run a tuned pipe/expansion chamber, or do silly head mods :D

    right! thats my rant!

    mind you, 89 is lower than what we get at the pump :whistling:
  4. 2strokepoke

    2strokepoke Member

    i don't understand why a fuel that doesnt burn as rapidly would cost more. Is it to be more efficient/ less impurities?? and explain why when I put 93 in my '57 Ford pickup it runs alot better than with 87?

    you are saying that with 87 you would actually get more performance than with higher octane? why do moped racers use high octane? :thinking:
  5. motorpsycho

    motorpsycho Active Member

    It's all about the compression ratio.
    anything higher than 87-89 octane in these little engines is a waste of money.
    you only need to run higher octane when you have an engine with high compression.
  6. HeadSmess

    HeadSmess Well-Known Member

    thankyou psycho :)

    all about compression ratio.

    also the size of the cylinders regards the pickup truck (can you post a pic pleeeeease? :) hope its a rat!)

    "rate of flame advance" increases with pressure(comp ratios???).

    raise the pressure, a fuel that burnt fast enough before is now too fast, and goes bang! thats not good.

    replace the fuel with something that normally burns a bit "slower" and it burns fast enough with the increased pressure... comprende signor?

    hi octane fuel costs more because;

    producing iso-octane (there are at least three varieties of the molecule known as "octane"...study the stuff and you shall realise why we want a specific one) requires "cracking" base petroleum products(ie, crude oil and volatiles) into their component parts...(propane, butane, methane, pentane, hexane octane cetane...get the picture?) then recombining these molecules via a catalyst (usually hot platinum wire...depends what youre doing...making ammonia requires red hot iron at over 100 atmospheres!) to produce the desired octane molecule :D we then mix this product with "benzene" a ring molecule we also extracted from our crude oil earlier. or something like that...

    make sense regards price? more work equals more money.

    you will find low octane fuels contain the larger percentage of "impurities"..acetone etc. and conversely less of the good stuff ;)

    good old tetra ethyl lead was cheap and raised octane numbers...til some fool decided that it was dangerous... :rolleyes7: makes ya dumb... i speak from personal experience, of course :p
    Last edited: Aug 23, 2011
  7. 2strokepoke

    2strokepoke Member

    thanks for the clerification Headsmess. I uploaded a few pics of my truck on my profile hopefully soon i'll have a few of my bike as well. :)
  8. HeadSmess

    HeadSmess Well-Known Member

    that is one sweet truck...even if its only 1/4 ratty :p if id had a decent shed/shop years ago i coulda gotten a 38 dodge flatbed :( i sorta regret that but i got a tuk tuk now...my childhood love, and i found and rescued it from the scrapheap by chance!


    i cant claim that one as mine...it belonged to the mechanic that worked on them originally. when i tracked him down he had just moved, thrown everything out, kept this one and some spares, wanted to sell... by the time i had the cash, hed vanished...and sold it to the company next door. they had then doubled the price, and left it out in a yard, uncovered, unregistered, couldnt start it, etc etc etc. heart breaking :(

    thats why i know theres only 5 that can be registered in Au :) and i got one of them! where is a pic of mine? iunno. i aint searching. lucky to find that one!

    oh! btw! i run 98 usually... thats 98. not 89.
  9. 2strokepoke

    2strokepoke Member

    Thanks! it turns alot of heads. Do they sell 98 at the pump there in Australia?
  10. HeadSmess

    HeadSmess Well-Known Member

    91, 95 and 98 at the pump :)
    i get 98 cus it smells nice and easier than messing around with different cans... also doesnt seem to go "off" as quick.
  11. 2strokepoke

    2strokepoke Member

    odd we only have 87 89 and 93 around where im at.
  12. dodge dude94

    dodge dude94 Member

    ^That's because gas (petrol, lol) in Aussieland is different there 'round here.
    We only have 87, 89, and 91 here.
    I use 89 for everything, found that I get better economy and it runs better.
    Everything, I use it for my truck, lawnmower, weedeater, chainsaw, gasbike....