91 vs 95 octane?

[Fast Eddie]

Why the duece do we get all these road bikers givin there 2 cents on this page?

haha.. cause an internal combustion engine is an internal combustion engine.. doesn't matter if its a 450cc single banger in a dirt frame or a 4 pot in a road frame

[Mort]

You should use the fuel rating your engine is designed for...using a higher octane wont make a bit of difference. If the engine is designed for 91, it will make no difference using 95 because the engine will not produce the compression that may cause detonation that 95 octane will prevent. (did I say that right ?) 95 is meant for higher compression engines.

There is one exception I agree with... if you are running at a trackday say, you really dont want detonation happening at high engine revs and if you got a dodgy batch of fuel (it happens) then you best mitigate that situation by using 95.... but you wont get anymore power from it.

[morg_nz]

98 - from gull only. there is way too much variability in nz octane ratings - i'e heard of some "91"s being as low as 85 - 87 in tests. at least if you run 98 you have a chance of getting a semi decent octane. and as bp and gull are the only ones with 98, and bp charges like 5c more per litre, go to gull. Also, its not like its race fuel - 98 aint going to blow anything up, it just burns way cleaner and better combustion = more power. simple.

[caspernz]

91 is fine for the lawnmower....

Car and bike can run on 91, but I find that I get more kms per tank if I run on 95 or 98 (where available). Over the years, tested it various different ways and for me the highest grade of fuel gives the lowest running cost, ie cents/km. The bike feels more lively on 98, good enough for me to use it where I can.

[CRF119]

All i can say is use the same fuel each time that way you know what your bike should perform like when you get to a ride. I always use BP 98 in every thing, ill go out of my way to get it. A friend of mine stopped by Mobil and brought 98 because he had no time to stop by BP, his bike wouldn't even run on it! We drained the carb and the tank put my BP 98 in and it started right up. I am sure my Van gets more Kms on 98, it can't retard the timing enough to run properly on 91.

[NordieBoy]

My VT250 and Nordwest preferred 95 but the XR250, DR650 and TT350 prefer 91 for a noticeable bottom end improvement.

The VT and Nordie were much higher compression than the others.

[JMemonic]

Just a little note, the octane rating is not, does not, and never will relate to the power a particular fuel will generate, it is a measure of how it burns in a controlled environment. 98 RON will deliver no more power in a vehicle designed and tuned for 91 than 91 will, if you want to spend the money dyno your vehicle same day same conditions just change the fuel and see if you get a increase in output.

RON in a measurement determined to a scientific scale, 91 RON in NZ is 91 RON in the US blah blah.

Further reading

Oh as a side note F1 cars are limited to pump gas at 91 octane, this is tested by the governing body.

[scott411]

in any late model 4 stroke mx bike i would run minimum 95 octane,

[p.dath]

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Does anyone have a preference and why ? Are there any pro's or con's to either ?

Thanks

I'm price sensitive, so I use 91.

[Jay GTI]

RON in a measurement determined to a scientific scale, 91 RON in NZ is 91 RON in the US blah blah.

Except that if you go to the US, you will see an octane number on the pump, as you do here and it will not be the same as you see here, because they list the PON, not the RON as we do. But if you'd read any of the previous posts...

[JMemonic]

Except that if you go to the US, you will see an octane number on the pump, as you do here and it will not be the same as you see here, because they list the PON, not the RON as we do. But if you'd read any of the previous posts...

I did, if you re-read my post I was not talking about what they display on the pumps, I stated that RON or research octane number is gained by a scientific test and thus will be the same no matter the country

[willytheekid]

Got PhatGirl tuned up to run on the cheap petrol ...mind you....Being a two valve guzzi, she would probably run on potatoe juice

Cost was my driving factor...not performance (As long as no damage to the engine occurs)

[Jay GTI]

I did, if you re-read my post I was not talking about what they display on the pumps, I stated that RON or research octane number is gained by a scientific test and thus will be the same no matter the country

Which, by and large, had already been covered.

[ICE180]

much better quailty 98 has had a much better refinery process
91 will go off quicker if left in a tank compared to 98 has happen to me

[onearmedbandit]

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I'm price sensitive, so I use 91.

Ever worked out how far a tank of 91 gets you compared to 95? You may find you get more km's per tank from 95 (note may) therefore giving you better bang for your buck.