can octane ever be too high??

[silvia S13]

Can the octane level ever be too high for a car?
For example, those NOS octane boosters, I am guessing they are really high octane, because they increase a couple octane points.  And if you fill your whole tank up with those, what would happen?  No, I would never do that, I am just curious.

[the3SecondJerk]

I was always under the impression that the higher the octane the harder it is to ignite. Therefore turbo vehicles are required to use it to prevent detonation. But don't quote me on that. As far as filling your tank with octane boost....only way to find out is to try it. Let us all know what happens...I'd guess you will never get the gas ignited and it'll just turn over.  But then again I am not an ignition fuel specialist.

[gabossie]

You certainly wouldn't have detonation, that's for sure. The only bad thing i could see coming out of it is that you wouldn't have enough money left over to make your next insurance payment &nbsp;<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/hehe.gif" border="0" valign="absmiddle" alt=':hehe:'> . I don't really know, interesting question though. Anyone have a more relevant answer, I am interested too?

[silvia S13]

Actually, I just thought of something, maybe I can ask my Chemistry professor, he should know.

[DSC]

I was on E and put 1/4 tank of 100 octane in my s14 and it ran just fine. &nbsp;I was told it can foul your o2 sensor from running so rich, but the o2 sensor seems fine (no codes thrown) so I guess it was fine. &nbsp;As for running too high, I'd imagine if you got up really high you could actually not have enough heat to ignite the fuel but I can't really see that happening, even at 110 you'd prolly just not have enough heat to ignite ALL the fuel but it'd still go boom and make the car move...just spit out unused fuel to ignite in the cat.

[blatch]

Yes, you are correct. The higher the octane, the harder it is to ignite. So for a turbocharged, inline-four, higher octane is good. But for a N/A V6 (like my accord) it turns out you get more horsepower from 87.

[gh6o6]

its my understanding that the octane boost doesnt make it harder to ignite, but not ignite in several places. &nbsp;Instead the burn starts by the spark plug and burns evenly through the combustion. &nbsp;Running a full tank (or only octane booster) of it will cause the engine to run extreemy hot, causing it to most likley need a rebuild

if you need a reference, search jet fuel - i think it was discused in one of those topics

[transient]

Yeah, the SR71 blackbird uses a jet fuel with an octane rating so high, that it will actually put out a match if you dropped one in a puddle of it. That definately wouldn't burn in your car <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'>

[mbmbmb23]

I heard the SR71 Blackbird uses a flammable gel for fuel.

The higher octane will definately give you more throttle response, but in some cars it will burn out the catalytic convertor faster than lower octane gas. &nbsp;I wouldnt use anything under 91 octane w/ a turbo....or anything over 94 octane period.

-m

[uiuc240]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (transient @ Sep. 09 2002,9:28)</td></tr><tr><td id="QUOTE">Yeah, the SR71 blackbird uses a jet fuel with an octane rating so high, that it will actually put out a match if you dropped one in a puddle of it. That definately wouldn't burn in your car <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'></td></tr></table><span id='postcolor'>
Not correct. &nbsp;The SR71 uses something other than jet fuel...and it is a gel. &nbsp;But this is something the switch over to after they go out of the first level of the atmosphere...then there is essentially no oxygen. &nbsp;

In fact, jet fuel is just kerosene, and it actually has a LOW OCTANE, being that it is more difficult to light a fire at higher altitude. &nbsp;This is the same reason that high altitude cities, like Denver have 85/87/91 instead of 87/91/93 like we do out here in Illinois. &nbsp;You don't need as much resistance to detonation, because the air is less dense and therefore less prone to ignition.

Bada bing.

Eric

[misnomer]

I've noticed no difference at all with high octane gas on my '92. Stopped buying high octane alltogether <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/tounge.gif" border="0" valign="absmiddle" alt=':p'> You really only need it if you are high compression or forced induction.

[240 2NR]

The blackbird also has to be refueled just after takeoff because the expansion undergone at mutiple mach speeds is so great that it is impossible to seal the fuel tanks, so while on the ground and durning takeoff will weep almost half its supply.


There is too much of a good thing and while a stock 240 may run on 100+ octane (I think over 108 conatins lead so it's a no no for cat equipped cars), it's probably not making any more power and is probably making less. &nbsp;Remember that even when nissan specifies 91 octane be used, it is still idiot proofed for people who run 87 (though again, power may not be ideal). &nbsp;

As for a tank of octane booster. &nbsp;I wouldn't try it as I don't think it conatins any gasoline, just like a full tank of any other fuel addative would probably not result in favorable engine output.

[Rownan]

What if my KA was running at 11:1 compression and the computer was tuned for higher octane pump gas like 93.. &nbsp;Would octane boost give a horsepower increase?

[AKADriver]

If it's tuned for 93, run it on 93.

Stock, they're tuned for 87 (SOHC) or 91 (DOHC).

Generally speaking, an engine will make the most power on the lowest octane that doesn't cause detonation, or in the case of a knock sensor equipped car, cause the ECU to cut in and retard timing.

Now, if you took that 93 octane, 11:1 engine, and used an aftermarket ignition box and/or messed with the distributor to advance timing, then higher octane fuel could be beneficial.

[Ni5mo180SX]

I think if you used to high an octane, you're car would have trouble igniting most of the fuel.

[the3SecondJerk]

right, also the higher the compression the pistons are the higher the octane must be. Nobody wants to hear their engine knocking do they? Thats why race cars and turbos use higher octane. Detonation! &nbsp; <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/cry.gif" border="0" valign="absmiddle" alt=':cry:'>

[/etc/shadow]

NEVER EVER EVER FILL YOUR TANK WITH NOS OCTANE BOOST. Some tard did that to his civic. The car never ran again.

[adey]

NOS octane booster adds a few points of octane, yes... but it doesn't make 91 octane gas into 95 octane, it actually changes 91 int more like 91.5 (or was it 91.05??). Their use of "points" is HIGHLY HIGHLY HIGHLY misleading.
That said, I'd follow ^his^ suggestion and NOT try it. it's a bleeding waste of money.

As for octane too high... I've run straight 100 (which isn't as high as one could go) in my VW GTi (1.8Turbo) and it felt absolutely GREAT, despite peoples' telling me it wouldn't make a difference (since the car was 'tuned' for 91 here in ca/93 elsewhere). I swear it pulled harder with 100 in there.
I think with higher octane gas you will also see a decrease in gas mileage. (or at least that's what I noticed.)

Were our KA24DEs made for 91??! i was told (was under the impression) that it was made for 87/89 octane... anyone still have their instruction manual? <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/confused.gif" border="0" valign="absmiddle" alt='???'>

[240 2NR]

The KA24DE (at least my 93) does in fact call for 91 for optimal performance.

[adey]

oh damn. &nbsp;<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/confused.gif" border="0" valign="absmiddle" alt='???'> &nbsp;I've been feeding the baby the wrong fuel the whole time. I guess it doesn't help that the last owner has been, too... <sigh> Thanks for going and checking up for me though! <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/thumbs-up.gif" border="0" valign="absmiddle" alt=':thumbsup:'>

[240 2NR]

I'm sure the stock timing is conservative enough that unless you're under full load on a really hot day going up a hill, 87 isn't going to kill the engine. &nbsp;At the same time, it should perform better on 91. &nbsp;Anyone know if the ECU "learns" the fuel you run and should be reset before switching to 91?

[tnord]

OBDII learns, OBDI does not, iirc

actually, i doubt it's that simple. <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/eh.gif" border="0" valign="absmiddle" alt=':eh:'>

[drifting240sx]

what year did they change to OBDII? i forgot, was it 94?

[tnord]

96 i think

[DSC]

I think some of that later year 95's had obdII as well.

[flipboi13]

No, I think its like 94 too.

[Nerfdude]

wait... so you're telling me that if i stop feeding my car 93 and start feeding it 91, it'll perform better? i'd actually save money AND get better performance?! ugh... what about engine knock, would it increase or decrease...
*will fill his tank with 91 on friday*

[silvia240]

Ok so i have been using 91 octane for about the past 3 years and a couple months but the guy before me always used 87 octane. &nbsp;I have noticed that i get better gas mileage with 91 than i do with 87 and i feel a difference, only on the highway, but for all i know that could just be in my head. &nbsp;So what i want to know is that what does everybody use because if i can save money and the car would feel the same, i would definately go to 87. &nbsp;But the manual does say 91 is recomemded for optimal performance. &nbsp;So what should i do?

[adey]

Duh! Maybe that's why my gas mileage is so unbelievably poor... on second thought, it probably isn't just the octane of the fuel I'm using. I'll try a tank of straight 91 next time.
<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/whatsthat.gif" border="0" valign="absmiddle" alt=':whatthe:'>
I tend to get crappy freeway gas mileage (trip to/from Irvine from/to Down Town LA used up over 1/3 tank) but it seems that spirited, high-rpm driving (a lot of gear shifting) doesn't drink nearly as much... <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/crazy.gif" border="0" valign="absmiddle" alt=':crazy:'>

[nrcooled]

I use 93 oct in the SR and have used 91 oct before. &nbsp;I don't really notice a difference. &nbsp;The only difference that I feel is that of the "hot outside->cold outside" &nbsp;When its cold the car is almost scarry fast but when its hot I might as well be rocking a n/a KA ::no offence KA dudes:: <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'> &nbsp;<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/tounge.gif" border="0" valign="absmiddle" alt=':p'> &nbsp;<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/hehe.gif" border="0" valign="absmiddle" alt=':hehe:'>

[guidot]

As far as I could tell, running with higher octane fuel isn't beneficial. &nbsp;I dumped a lot more fuel running a straight 1/4 tank of 100, than with 93. &nbsp;I was on track to hit 300mi per tank, whereas I can squeeze 400 out on 93. &nbsp;

The S14 is meant to run on 91 or better (according to my manual). &nbsp;The s13's could run on 87+. &nbsp;

And don't get me started on octane booster. &nbsp;Even if that whole bottle was 100 octane, there is no way it could raise 16 gallons of 87 fuel a "few points." &nbsp;When they say points I think they mean 0.XX points!!

[adey]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (guidot @ Sep. 19 2002,11:54)</td></tr><tr><td id="QUOTE">The S14 is meant to run on 91 or better (according to my manual). The s13's could run on 87+. </td></tr></table><span id='postcolor'>
I seem to be hearing contradicting things... so should I run my '93 RMS13 on 87octane, 89, or 91 octane gas??

[teamcapsule]

Here in Belgium we have leaded and unleaded gas. Unleaded comes in the form of 95 octane, 98 octane and even 99 octane. But most cars run on 95 octane.

[silvia240]

So anybody have an answer to my deeply intelectual question (i hope i spelled that right)?<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/confused.gif" border="0" valign="absmiddle" alt='???'> &nbsp;Cauz if i can save some money, and there is really no difference between 91 and 87, i would like to use 87 and save some money cauz right now its either my car eats or i eat... Poor student life is not fun. &nbsp; <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/sad.gif" border="0" valign="absmiddle" alt=':('> &nbsp;<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'>

[240SxTYLE]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Posted on Sep. 18 2002,10:12
--------------------------------------------------------------------------------
wait... so you're telling me that if i stop feeding my car 93 and start feeding it 91, it'll perform better? i'd actually save money AND get better performance?! ugh... what about engine knock, would it increase or decrease...
*will fill his tank with 91 on friday*</td></tr></table><span id='postcolor'>

yeah im in the same boat as nerfdude... i wanna save me some money too... besides if its better for my baby than im all for it. so please can anyone answer this question? thanks

[AceInHole]

it's funny what happens when school and cars mix...

anyways, the long answer is here (http://www.howstuffworks.com/question90.htm).

the slightly shorter answer (based on both the above answer and recent Mech Eng knowledge) is that an octane rating is based on the percentage of octane and heptane. &nbsp;91 octane = 91% octane, 9% heptane. &nbsp;ratings above 100% have some chemical with a higher heating value than octane (such as methane or hydrogen i'd guess). &nbsp;the reason why more octane is better than more heptane is that octane handles compression MUCH better. (also note that hydrogen has more than twice the lower heating value of octane, and produces about 0% the pollution of octane [running on memory that this is H2 compared to H2C8, and the Carbon atoms form the CO that pollutes]). &nbsp;

in short: octane = handles compression better than heptane, heptane contains less carbon atoms than octane, so as long as your engine isn't knocking, i'm guessing: more octane doesn't = more power, but pure octane will still let your engine run.