High octane petrol/gas question

[Swipe]

I always fill up with regular unleaded 91 RON but I've seen various threads on other motorcycle forums where people swear by higher octane fuels such as Shell Optimax and suchlike @ 95 RON. Would higher octane fuel suit the Hawk/Bros and offer any extra performance or should I stick with regular unleaded?

[ghandi1616]

If your bike is running good on the gas that your are using there is no sense in switching. The higher octane is best suited for higher compressions.

[Doc]

ditto the above.

Although the lowest I can get at the track is 93. I run 89 in the Ducati without problems, I htink it runs worse with higher octane actually...

[MrDude_1]

this is an oversimplifacation but...


lower = better.



octane is resistance to detonation.... in otherwords, the resistance of the fuel to spontaniously ignite.


the higher the number, the harder it is for it to ignite.




why would you want this?

lets pretend you take your hawk, and you up the compression to 12.5:1.....
now that lowtest fuel you were using gets compressed, and POW!!! lights off early... this creates a pressure spike... that "ping" you hear from it detonating.... this is like hitting your piston/head with a hammer.. its bad. lol.


ok, so what would your options be? well, you could lower the compression.... or run higher octane.
the fuel will burn slower, but it wont light off early.. so this loss isnt too bad, you just change the timing to compensate, and because of the higher compression, you endup with a overall more powerful motor.









now, take your bike as it is now, and run it.. it runs great on low octane....
but at higher octane.... well, it still has the low octane timing... it doesnt have anything to gain from the higher octane.. it doesnt have any modificatiosn to take advantage of it (like higher compression for example).. but it will lose a SMALL amount of power.





you put higher octane then needed in a motor, and all it does is cost money.






theres alot more to that, but thats it in a nutshell

[Ribbit2]

There's far more important stuff to a fuel than the octane rating.

As I see things, it took decades to get the additives for leaded petrol right.

Then we got unleaded dumped on us, with its atrocious additives. It really was a fuel totally unready to go to market, IMHO, and remained so for far too long (for example my fathers car was almost wrecked with the rubbish unleaded fuel from a major Supermarket petrol point - wrecked the cat, and the engine management simply couldn't cope with it).

To me, Shell Optimax was the first unleaded petrol available to get the additives even remotely approaching right.

You would not believe the difference running on Optimax made to my BMW K75S (hardly a highly stressed motor - but rubbish fuel was certainly stressing it out).

I try and run 50/50 Optimax/A.N.Other Fuel as a minimum - just for the additives in the Optimax (or whatever its replacement now is).

There's a difference, and I notice the difference.

There's a couple more high grade fuel options available here now, and not before time (they should be paying *US* to burn the other stuff for them! ).

[MrDude_1]

There's far more important stuff to a fuel than the octane rating.

As I see things, it took decades to get the additives for leaded petrol right.

Then we got unleaded dumped on us, with its atrocious additives. It really was a fuel totally unready to go to market, IMHO, and remained so for far too long (for example my fathers car was almost wrecked with the rubbish unleaded fuel from a major Supermarket petrol point - wrecked the cat, and the engine management simply couldn't cope with it).

To me, Shell Optimax was the first unleaded petrol available to get the additives even remotely approaching right.

You would not believe the difference running on Optimax made to my BMW K75S (hardly a highly stressed motor - but rubbish fuel was certainly stressing it out).

I try and run 50/50 Optimax/A.N.Other Fuel as a minimum - just for the additives in the Optimax (or whatever its replacement now is).

There's a difference, and I notice the difference.

There's a couple more high grade fuel options available here now, and not before time (they should be paying *US* to burn the other stuff for them! ).

ummm... what?

are you talking about ethanol blends or something?

[Ribbit2]

No this is straight unleaded (I don't think we have ethanol blends over here yet - though with the appalling rubbish some Supermarkets sell as petrol, I do wonder what on earth they include in some of theirs).

These are the flame shaping/altering/lubing type additives that are so critical (for example there's some good 95 octane fuel over here that has good additives, and some really crap 97/98 octane that has awful additives, and runs no better than putting paraffin in your tank ).

The only 'independent' combustion additives I've ever used, are large quantities of toluene (friend used to get 25ltr drums of it in bulk - though you can trickle in carb cleaner into the tank as it's the same stuff and quite cheap - careful though, it's highly carcinogenic, so DOWNWIND) for a turbo powered car that seemed to really need high octane aviation fuel before it would stop pinking, and some Nitrous Oxide years back when I nearly went drag racing with a Kawasaki 900.