Join Date: Feb 2012
Location: coogee beach australia
Thanked 1,303 Times in 809 Posts
'research octane number' = RON..
91RON = [approx] 86/7PON [usa]..
compression ratio is one element of combustion
chamber design and engine 'tuning', based on
various parameters including flame throw
or shape thus burning rate..
higher combustion requires slower burning fuel,,
ie, higher octane rated fuel..
[cbr600rr for eg cr = 12:2:1, moto3 250 = 15:1]
in our combustion chambers at cr 10.7:1
we dont need slower burning fuel
which wont/cant work better in
at higher cr pressure etc increases risk of
pre-ignition [bad], thus slower burning fuel
[higher octane] is used to suit that cr etc,
so as to avoid pre-ignition..
[high performance engines typically have higher cr
thus require/use higher octane fuels,, which has
created the false idea that high octane rated fuel
gives more hp,, ie, in low cr engines]
if your honda tech has recommended using higher octane
fuel, you should ask him why this is so, in particular
if he has detected signs of pre-ignition, etc..
also, 'premium' used for petrols is not a tech term
meaning 'better' etc, rather premium relates to
cost or the consumer, the premium you pay..
there are additive packages in premium petrol
typically intended for car/truck etc engines,
which are not designed for this 250 single..
you pay more for, the additive package..
basically, your engine will work better, on faster
burning [lower octane] petrol..
some authorities claim that using high octane
petrol in low cr engines can cause damage
over the long haul,, yet members here have
used higher octane with no obvious
harm and barely discernable difference
in general performance..
ive used it a few times to avoid ethanol
when low on fuel at night etc..
no obvious difference [altho it is also mixed
with whatever petrol is still in the tank]
over known routes etc..
no increase, in performance..
those are the basics of the question
as its been thrashed out here and
on other forums etc..
use search box or search
honda recommends 91ron [86pon] 'or higher'
'or' means an alternative to that recommended,
which could be possible given symptoms of
pre-ignition etc.. quality of petrol could be
a factor, which is one reason i and others
recommend using known medium/high
turnover outlets [fresher/cleaner fuels]
and no ethanol..