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Hi
Another stupid question of mine. I've been reading about Octanes in
gasoline, and according to around 90% of websites there is no real benefits
from a higher octane. Is there any real benefits? Or difference?
triggerman
There is absolutely no benefit to using a higher octane gasoline than the
engine requires. Using a higher octane than needed can actually reduce the
efficiency of your engine, cause you to get worse gas mileage and put out
less power.
vwhobo
There is absolutely no benefit to using a higher octane gasoline than the
engine requires. Using a higher octane than needed can actually reduce the
efficiency of your engine, cause you to get worse gas mileage and put out
less power.[/QUOTE]
Alright thanks, well how do you get worse gas mileage? I've been told
using a higher octane gas helps the engine if it's a "high performance
engine" What exactly would or could be considered a high performance
engine?
triggerman
Alright thanks, well how do you get worse gas mileage? I've been told
using a higher octane gas helps the engine if it's a "high performance
engine" What exactly would or could be considered a high performance
engine?
triggerman
1. As I said in the previous post, decreased efficiency.
2. More correctly you need higher octane in a higher compression engine.
I can't give you a specific number because it depends on factors such as
engine design, materials used (aluminum or cast iron) and the powertrain
management system. Generally speaking the newer (technolgy wise) the
engine, the higher compression it can run before an increase in octane is
required.
vwhobo
Ok im a little confused, cause my car only requires 91 octane, but when i
put 100 octane in there it re-adjusts the timing and runs faster smoother
and i get better gas mileage, so when you say no gains do mean once you
reach the optimal octane for your engine ( which in my case is way above
pump gas ) or when you go above what your car manual says ( which in my
case is 91 ).
VrrmPshh
In your case what I'll say is you have a great imagination. If your car
requires 91 octane, that means it is optimized for 91 octane. Running 100
octane is a waste of money.
vwhobo
don't most vehicles have programming built into the 'puter that allows
lower octane through various tricks?
ie: retarding timing
leaning out the AF mixture
(if Forced Induction) lowering boost
it's just that they get the optimum power curve at X octane, but they can
survive on Y octane
right?
asa67_stang
You're right, although it depends on how smart the PCM is. Most cars get
by with a knock sensor which retards the timing when detonation is present,
some are a little more advanced then that. However that's a short term
solution, if you regularly run gas with too low an octane rating there will
most certainly negative long term results.
vwhobo
good thing i told my mom she's been runnin too low of an octane on her
Passat then, eh?
i was suitably impressed by that 1.8T and how well the rest of the car
worked together, very nice
asa67_stang
I wish i had more then just my "butt dyno" to prove that running a higher
octane in my car was increasing its efficiency and performance, but i dont
so i wont even argue the point as it is all goin off my word. I did however
look in my manual to see if there was anything on running a higher octane
and only found that it said use "at least 91 octane" which leads me to
believe that perhaps 91 is not my car's optimum octane rating its just what
subaru feels is the lowest you can go without any negative side effects.
Now im not sayin 100 octane is my car optimum rate either but im going to
do a little more research ( gradually increasing octane until i can no
longer feel a difference ) to figure it out...i guess i could also just
call subaru and ask them..but wheres the fun in that
VrrmPshh
where do you get 100 octane gas?
:umh:
SuperJew
.
.
You can read some "official" data here:
http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm
...but who really trusts the government anyway...
:smoke:
BavarianWheels
some gas stations sell GT-100, but i use 91 octane then add toulene
acorrdingly heres an article on it that pretty much explains it all
http://forums.audiworld.com/s4/msgs/95187.phtml
it also explains that newer cars (like mine) do benefit from higher octane
gas
VrrmPshh
toulene is very harsh on rubber, dunno what effects it has when dilluted
through gasoline
asa67_stang
gasoline is pretty harsh on rubber too though so im not worried about
it....
VrrmPshh
Running toulene for an octane boost is nothing new, my father was doing it
in the '50's in his '49 Merc lead sled.
If we're going to do something stupid and dangerous, why don't we go all
the way. Let's run xylene (117) as an octane booster, after all it has an
even higher octane number than toulene (114). Of course some of the short
and long term effects of having either in your fuel system are rotted fuel
lines, damaged injectors they can even decompose your plastic gas tank.
And if you run them in high enough concentrations you'll damage your
catalytic converter(s) and your oxygen sensor(s). Cheap parts to replace
I'm sure you'll agree.
Better yet, I can get you a really good deal on some MTBE (118). Any
takers?
vwhobo
actually, there's a guy at FSP (my inline six forum that i hang at) that
flirted briefly with all of those...
notice i said briefly, he knew what it could do to the various parts, he
just wanted to see what he could get away with without pinging
asa67_stang
I run 116 octane in my car, and it works just fine, I don't get whats so
stupid about it, as a matter of fact, if I don't run it diluted with a
premium, my car gets minor detanation, and runs lean, my RPM will increase
by about 400, and my intake sounds like it's a vacuum. Of course if you
don't have a car that will handle the fuel properly, and you think you're
some kind of racer when you aren't, don't run it, because it will harm your
engine, I designed my engine specifically to run at a higher compression.
Logicalbomb
Octane basically says how much compression it can handle without knocking.
In "high performance" engines, the compression ratio is higher, so low
octane fuels won't be very good as you might get spontaneous combustion (ie
explosion without the spark).
windsonian
As silly as it sounds, octane ratings are about how slow the fuel burns. I
think, but don't quote me on this, that 91 octane under x pressure at y
volume takes 91 milliseconds to combust. 100 octane would take 100
milliseconds under the same conditions and so on and so forth. For most
street cars produced in the U.S. they are set to run on like 87 or 89
octane and too much more than that is indeed a waste of money. As for
adding chemicals to increase octane ratings, be very careful and remember
that all of the previous batch has not been run out. :2cents:
srober32
Octane rating is a measure of the "anti-knock" properties of gasoline, and
doesn't have much to do with combustion speed. It is not measured in
milliseconds, either. Consider what would happen if you used 98 octane
gasoline in an engine with huge pistons (many liters per piston). Would
this gasoline combust in the same amount of time as 98 octane gasoline in a
normal cylinder (0.5 liters)? Obviously not. The flame front would move
at a similar speed, but because of the greater size, the combustion would
take longer to complete in the larger engine.
Here is the real story, and the first eight hydrocarbon names:
1 Methane
2 Ethane
3 Propane
4 Butane
5 Pentane
6 Hexane
7 Heptane
8 Octane
.....CH3..H..CH3
......|...|...|
CH3---C---C---C---CH3 <-- Iso-octane
......|...|...|
.....CH3..H...H
Iso-octane, otherwise known as (2,2,4-trimethylpentane) is very
smooth-burning, and is assigned an anti-knock rating of 100. Heptane, on
the other hand, is very susceptible to knock, and is assigned a rating of
0. The gasoline you buy at the pump is rated on a scale from heptane to
iso-octane. An octane rating of 93 means the gasoline has the same
anti-knock rating as a mixture of 93% octane and 7% heptane. An octane
rating greater than 100 indicates that the fuel is even less susceptible to
knock than pure iso-octane.
You can see a sticker at the pump that says "calculated using the (R+M)/2
method". The R is the Research Octane Number, from an engine running at
600 RPM. The M is the Motor Octane Number, from an engine running at 900
RPM. The two are averaged to provide the total octane number you see at
the pump.
I hope this dispels some of the myths floating around.
lithiumdeuterid
Well it sure shut the thread down. I guess now Satty will come along and
lock it. :banghead:
vwhobo
I heard that higher octane burns either faster or with more temperature and
can help clean the valves.
newyorker
Once again you heard wrong. What a surprise. All you had to do was read
the thread and at least one of those is covered.
vwhobo
Better do some reading on that subject. There are plenty of research
articles the confirm that running gasoline with an octane rating higher
than required actually decreases power output.
vwhobo
In a completely stock car you are better off switching from the cheap stuff
to the premium fuel if you are selling it. If someone is test driving it
and puts the pedal on the floor it is less likely to rattle if something
doesn't go just right and you might only have the one chance on a test
drive.
If you run high blower, or turbo boost, or have a performance chip and find
that your car preignites at high load use higher octane gas or ethanol
(if you can get it). If you raise the compression above the stock
compression ratio then you will need higher octane gas or ethanol if it
preignites under load. Check your base ignition timing as well as your
advance curve before stepping up at the pump. Additives cause crappy
deposits. If you are worried about rubber seals then step up to Viton as it
is easy to get and holds up to gas additives and ethanol both (sometimes
better than aluminum).
Octane is strange, as is the Cetane rating of diesel. Research the BTU
ratings if you switch fuel types. Ethanol doesn't preignite in the real
world and you can always add more but the lower BTU means you need to
fatten it up (nearly 40%) to get the same amount of power. To get even more
power with ethanol you can run much more compression and boost, then watch
your oil turn green. It shouldn't cost as much to run ethanol as 116 octane
gasoline.
If the 100 octane mentioned is blue then suspect it is a low-lead aviation
fuel and don't run cats or you will cook them.
I have a diesel car I run with biodiesel and regular diesel. The cetane is
about the same in each but the BTU in the biodiesel means much worse
mileage and it costs more. Used to pitcrew for alcohol dragsters and can
not wait until that stuff is available on the street. Nice complex topic...
electrodes
Too many guys no too little about cars
Wally
You're 110% correct on that. I usually run on 87 octane in my T-bird with
16* base timing and about 38* total...from what everyone else says they've
experienced, I shouldn't be able to do that without some
detonation...probably because I'm not running the E7TE heads, but rather
the larger chambered E6SE heads. It runs slightly better on Sunoco 94 at
the track.
Just a few months ago, I went to Atco Raceway and ended up making twice as
many runs as I had planned...leaving me in a slight fuel crisis, didn't
think I could make it home on what I had. I went to the pumps and the
lowest octane I could find was like 104...I bought $30 worth...about 5.25
gallons, just to get me home. After that, the car ran like absolute sh!t,
started surging real bad at idle and didn't want to make power. After
about 5-6 fill-ups of 87, it was back to normal. Car still surges
slightly...but that's due to needing a new TPS sensor.
Sick88Tbird
