Lamborghini Talk banner

1 - 12 of 12 Posts

·
Administrator
Joined
·
5,166 Posts
Discussion Starter #1
How bout a little insight into what octane actually does. Does it make a more powerfull explosion during the combustion cycle? I can find 91 octane all day long, rarely 93, just how much difference does it make. Is it worth using a so called octane booster I've seen on the store shelfs?
 

·
Premium Member
Joined
·
1,156 Posts
raymondo said:
How bout a little insight into what octane actually does.
Fuel can be ignited by spark or compression. In simple terms, the octane rating says how well the gas can be compressed without igniting. If the gas ignites by compression you get "knocks" - bad. Thus if you have no knocks, you probably have the "right" level of octane.

Higher compression engines need higher octane fuel thus the different octane offerings. Putting in a higher octane fuel than is needed by your car to avoid knocking (compression ignition) is a waste since you are either knocking or not. Octane itself does not dictate the explosive force - the compression of the engine does.

Technically, cracked crude oil produces: methane, propane, butane, pentane, hexane, heptane and octane. Octane is the best at handling compression. An octane rating of 91 means that 91% of the fuel is "equivalent" to octane (close enough for this discussion). "Equivalent" since things like lead can be used as cheap octane fillers.

-mick
 

·
Registered
Joined
·
104 Posts
I use 100 in Nv and the cars run a little quiter and quicker, when I'm in Ca I use 91. The difference isnt that much. I have done this on many cars over the years with about the same results.
 

·
Registered
Joined
·
66 Posts
with the exception of high performance cars, i've heard that if you fill your "high octane only recommended" car with a lower octane fuel, it's not a big deal with modern fuel injection. the engines are supposed to adjust to a lower compression fuel and not knock. anyone know if this is accurate? if an engine knocks, what sort of damage might occur over time?
 

·
Registered
Joined
·
93 Posts
Dunno about newer Lambos but the manual for my Countach states very clearly that you must not use anything less than 97 Octane fuel. However mine is a normally aspirated engine - the US ones are fuel injected so can probably get by with the inferior American fuels.

97 and even 98 Octane fuel is in plentiful supply here in the UK as BP Ultimate and Shell Optimax respectively.
 

·
Premium Member
Joined
·
1,156 Posts
henrus said:
with the exception of high performance cars, i've heard that if you fill your "high octane only recommended" car with a lower octane fuel, it's not a big deal with modern fuel injection. the engines are supposed to adjust to a lower compression fuel and not knock. anyone know if this is accurate? if an engine knocks, what sort of damage might occur over time?
This is true... many modern cars (and that includes most high performance cars) have knock sensors that provide feedback so the car can adjust air/fuel timing etc. This also "fixes" other issues like altitude and temperature etc. And this is whats also behind the myth about higher octane=always better since knowing if the knock sensor is retarding things is not easy to know.

At some point as you increase the octane level, the knock sensor will not detect anything wrong and the cars computer will run things optimally including designed/correct performance. Increasing the octane level at this point does nothing except hurt your wallet.

Now exactly what the correct octane levels are for our various cars seems to be the bigger mystery :)
 

·
Banned
Joined
·
0 Posts
Highest I heard, was around 110. Never used and/or seen it, but I think it exists. Friend says its rocket fuel. BS, I think. :confused:
 

·
Registered
Joined
·
48 Posts
Taoist said:
97 and even 98 Octane fuel is in plentiful supply here in the UK as BP Ultimate and Shell Optimax respectively.
I wouldn't say plentifull, but yes its not hard to find.

We have 95 as the base (never seen lower). Then BP/shell have 97/98.

Problem is its only on certain pumps, so when the station is busy (quite often in London) its a pain to wait for a specific pump (and manouver urself to the correct pump without annoying people in the queue).

I was told 98 is optimum for the G, but using 95 wont hurt it (just performance). So I put in 98/97 when its conveniant, not as a rule.
 

·
Registered
Joined
·
464 Posts
I only use 100 Octane but it seems to burn much faster then 91
(the highest in ca)

I would rather be safe than sorry
 

·
Premium Member
Joined
·
1,156 Posts
5to1 said:
We have 95 as the base (never seen lower). Then BP/shell have 97/98.
In comparing octane ratings its important to know that there are three ways to measure things. RON (Research Octane Number), MON (Motor Octane Number) and AKI (Anti Knock Index). The AKI is the average of RON and MON normally seen as "R + M / 2" on the pump. RON is 8 to 10 numbers higher than MON. MON is the measure under harsher (eg performance) conditions than RON. Australia and Europe typically use RON. The USA uses AKI. The Octane level a car needs is the Octane Number Requirement (ONR).

So for example, an AKI of 87 would be 92 RON and 82 MON. So California's 91 AKI is equivalent to about European 96 RON so the difference between US and Europe isn't as bad as it appears.

-mick
 

·
Premium Member
Joined
·
1,156 Posts
sk90077 said:
I only use 100 Octane but it seems to burn much faster then 91
(the highest in ca)

I would rather be safe than sorry
Interestingly, the higher the octane rating the slower the fuel burns and there is no more energy produced (just because the octane number is higher).

Since our Diablos probably need something like a AKI 93 rating and you can't get than in California (at least easiliy) then 100 is probably the best bet so as to cover the cars octane requirement (ONR). On the other hand and assuming I'm correct on the AKI 93 requirement, putting in 91 is fine since the computer and knock sensors will deal with it - noting that its not optimal and thus not 100% of the performance the car can deliver.

-mick
 
1 - 12 of 12 Posts
Top