Octane

[Killtodie]

I think I have been ignorant on the matter long enough.

 

 

What I have always though of octane was, higher rating = better quality gasoline, and higher rating = provides more power for high end cars.

But I dont think that this is quite true.

 

I know that the higher the octane the less prone the gas is to ignition, but how does that translate to some cars needing 87 while others cant run on anything but 92.

 

Some other questions I have

-What happens if 87/89 is poured into our Starquests? Like if you run out of gas and the only thing the tow drive has is 87 and wont go get 93.

-I've been using 93 in my 01 Civic since the day I bought it, waste of money or does it have some benefit?

 

Example I have, I used to drive a 2004 Beetle, it took 87. One day I decided to fill it with 93. I immediately felt the car gain additional power and a lot more mileage. Was that just a fluke?

 

Back to my Civic, do I get any benefit of using Ultimate or 93? Gas companies advertise that Ultimate gas is better quality and has some added ingredients to keep engines cleaner. I'm also under the impression that 93 octane gas gives better mileage and burns cleaner. Now the added mileage might not outweigh the extra price for gas, but a better quality gas might be better in the long run.

 

mmmhmm

[Fanta]

It has something to do about the burn ratio or rating or something

 

Honestly, a Starion CAN run on 87 alright. Just keep it out of boost.

 

http://en.wikipedia.org/wiki/Octane_rating

 

That may help?

Edited April 26, 2010 by Fanta

[Starwolf]

If your car is pretty much stock...put the gas that the manufacturer recomends (your civic PROBABLY only needs 87)

 

As far as the beetle i would think its just a fluke or a butt dyno fail.

 

With a LOT of mods like much larger turbo and higher boost then you will need higher octane to get more power out of it.

 

Newer turbo cars recommend and should use 91-93 octane like the bmw 335i's

[Killtodie]

I read that wikipedia entry before, it wasnt 100% clear to me

[JAinsworth]

If you put a lesser octane in than is recommended by the manufacturer, you will get ignition knock. When a starquest detects this (via the knock sensor mounted near the oil filter), it retards the timing approximately 8 degrees to protect the engine. Therefore you will get worse performance.

Jimmy

[Project83]

I have noticed a difference in most of my cars if i use premium vs. regular not in performance so much as idling better and starting up faster. My Nissan pick-up seems to have a bit more pep pulling hills with premium but more just smoother running in general. I usually always ran 91 octane in my starion and will probally continue to do so after it's running again.

[Killtodie]

I never tired 87 in my Civic, so I dont know how different it would run.

[carguygibby]

Your stock Civic will run fine on 87 octane, put anything higher in you are wasting money.

As long as you use at least the lowest recommended octane for your car it will run fine.

Colinhttp://www.starquestclub.com/forum/public/style_emoticons/default/cool.gif

Edited April 26, 2010 by colingibb

[strang3majik]

higher octane is more difficult to combust, however, because of this, it can be more precisely ignited.

 

lower octane fuel is easier to combust, therefore, it is more prone to preignition, which can lead to detonation.

 

So, run premium in your quest at all times unless necesary. If necessary, just stay out of it and keep the rpms low and stay out of boost. In all actuality, all these engines need is 87 since they're only 7.5:1 compression. Its when you start pouring 10lbs of boost into them that creates the need to run higher octane fuel.

 

Because, higher compression = more heat = more prone to igniting the fuel before the plug actually fires.

 

Also, putting a higher octane fuel in a motor that doesn't need it will not do anything for you. Might make it a little bit more responsive, but, you won't really see any gains.

[Technology]

I think at stock boost levels on a stock car, 87 octane would be absolutely fine. You can even use 5w30 oil in a stock car when it's cold out. They are pretty much just like every other engine out there. In my car I use e85, which is around 110 octane. But you can't wheeze the ju-uice.

[ucw458]

Ok since it hasn't been explained fully so I'll try to put it in laymens terms.

 

 

When you compress a gas you get what's call "heat of compression" The air being compressed in your engine already has thermal energy in it. When compressed in the engine the thermal energy in the air is concentrated into a smaller space which raises the temperature. Energy is also added from physically being compressed. So a higher static compression ratio and/or higher boost will increase that temperature.

 

Every combustable material has a flash point. That is the point at which at a certain temperature the material will spontaneously ignite. 87 octane has a lower flash point than 92 octane. Pre-ignition or detonation inside an engine happens because while the fuel and air are being compressed it reaches it's flash point before the spark plug is supposed to fire. Since combustion is happening too early it puts alot of stress on the engine and can destroy it. Having a lean mixture will also lower the flash point and cause detonation.

 

So how do we get around reaching the flash point too early? Simple, use a fuel with a higher flash point. A common example is switching from 87 octane to 92 octane fuel. That raises the flash point and allows you to run more boost and/or a higher static compression ratio without harmfull side affects.

Edited April 26, 2010 by ucw458

[Killtodie]

So is there any benefit to running a higher octane fuel in a vehicle that recommends regular?

Better gas mileage?

Cleaner burn?

added cleaning agents?

not worrying about knocking

[ucw458]

So is there any benefit to running a higher octane fuel in a vehicle that recommends regular?

Better gas mileage?

Cleaner burn?

added cleaning agents?

not worrying about knocking

 

No, if 87 is reccomended for your car then use 87. The higher grade gas will be a waste of $. It wont burn cleaner. It may actually raise emmisions slightly. You will not get better gas mileage. Again waste of $. Only use higher octane fuel if it's reccomended by the manufacturer or you have modified your engine to the point of needing higher octane to prevent detonation.

[vbrad511]

It makes no difference to me what any manufacturer's book says, or what the scientific breakdown is supposed to mean. I am right there with the OP when he said he got better milage and more power. I've noticed it in all my vehicles when I switched. And I can tell when I get stuck having to run a lesser octane too. And to me, running the better stuff translates to a more efficiently running engine, which means an easier and longer lasting engine. It's worth the extra couple of bucks at fueling time to have that little peace of mind, whether the book calls for it or not.

[JAinsworth]

I run 93 in my lawnmower and 2 cycle mix. I bought my son a Husquavarna blower/shredder for Christmas. During the course of researching the best blower, I read a lot of comments about having to run the higher octane and I believe the owner's manual states it also.

 

My Malibu calls for 87, I'll run a couple of tanks of 93 and compare the gas mileage...can't really compare the performance, it has none.

 

Jimmy

[ucw458]

It makes no difference to me what any manufacturer's book says, or what the scientific breakdown is supposed to mean. I am right there with the OP when he said he got better milage and more power. I've noticed it in all my vehicles when I switched. And I can tell when I get stuck having to run a lesser octane too. And to me, running the better stuff translates to a more efficiently running engine, which means an easier and longer lasting engine. It's worth the extra couple of bucks at fueling time to have that little peace of mind, whether the book calls for it or not.

 

Butt dyno doesn't count. Unless you've had dyno tests to prove what you are claiming you may be fooling yourself. There's a difference between mentally thinking it's faster and it actually being faster.

[JustPaus_88TSi]

Higher or lower pump gas octane doesn't contain any more or less energy, it's just a heat/flashpoint issue like ucw458 mentioned.

[theRobot]

So, what about in the event of a N/A engine that has a very high compression? Say, 20-30 lbs higher in every cylinder compared to spec?

Would a higher octane be better for it? Seeing as it could be a change in the Comp-Ratio?

[vbrad511]

Butt dyno doesn't count. Unless you've had dyno tests to prove what you are claiming you may be fooling yourself. There's a difference between mentally thinking it's faster and it actually being faster.

I have no dyno...no scientific data. I just know when my car or truck has the higher octane in it it's got a little more get up and go. And it's not like I aded a big turbo or nitrous, but it's a notable change. I don't need a printout or a spec sheet to tell me there's a difference. I discovered the different MANY years ago, and have been back and forth between the low and high octane fuels, and I ALWAYS come back to the 92-93. Add to it the added gas milage and it tells me things are running better.

[mikec]

ucw458 explains what octane does for a motor - why some cars require only 87 and some require higher octane. Any time you compress air (or air+fuel) the temperature of that air rises: the turbo in your StarQuest (thus the intercooler to lower the temps again), the air compressor in a shop (notice how hot it gets while working?), and the air+fuel in the engine cylinders as the piston compresses it. Higher compression ratio = higher temps as the air+fuel is compressed. Eventually it gets too high as ucw458 explained.

 

Newer cars with electronic ignition timing (compared to centrifugal weights & vacuum advance mechanical systems) can take advantage of higher octane fuel; that's why folks notice an apparent MPG and performance benefit when going to higher octane fuel. Such cars use the knock sensor to detect the onset of detonation or pre-ignition; the ECUs in those cars increase ignition timing until the knock sensor says "okay, that's enough." Mechanical ignition timing stuff, like a StarQuest, isn't that precise and repeatable so Mitsu had to dial in "safe" timing levels... they aren't optimized based on the knock sensor like more modern ignition systems. Generally the more timing advance you can run the better/more efficient the burn. It may or may not be a big enough change to justify the extra cost of 92 octane over 87 though depending on the engine.

 

The actual ignition timing an engine can use depends on a lot of factors:

* basic compression ratio

 

* any carbon buildup inside the engine (raises effective compression ratio)

 

* turbo boost pressure (really raises effective compression ratio; 88-later StarQuests are 7.5:1 static compression but somewhere around 15:1 at max boost)

 

* ambient air temperature and density (i.e. what's the starting temp before we raise the temp during the piston's compression stroke); low density air doesn't pressurize as rapidly as high density air. So at high altitudes you can run more timing - even the old style StarQuest can do that. At high alts, the ECU sends a signal to the ignitor module to add 5 degrees more timing advance. More modern ECUs will add even more... until the knock sensor says "enough."

 

* type of engine coolant flow - normal or "reversed" flow. Engines used to circulate the water from the radiator, through the engine block, and then to the cyl head and intake manifold. This way the water was warmed by the block and kept the head & manifold warm enough so that ice wouldn't form in winter and gas wouldn't condense out of the air+fuel mix in the long intake manifold tubes. Well... with port fuel injection, or today's direct injection, there isn't any gas in the intake manifold anyway - so just keep it warm enough to avoid ice formation. Most cars today use a "reverse flow" cooling system that takes the radiator water through the cyl head and intake manifold first (thus keeping those parts even colder than an old style block-then-head system) and then the water goes to the block and back to the radiator. With the intake manifold a bit cooler (compared to the old style setup) there is less heat transferred to the air going into the cylinders - so it's cooler and more dense. A cooler cyl head is less likely to detonate too - that's why most reverse coolant flow engines have higher compression ratios.

 

An old non-performance engine, especially a carb setup, might actually perform slightly worse with high octane fuel compared to the octane it was designed for. It's a total waste of money for me to put 92 into my 1978 Corolla.... it's "high compression" for a 70s engine but rather low by today's standards. No knock sensor or anything... so it can't/won't auto-adjust for higher octane fuel. Using high octane fuel would cost me more money at the gas pump and probably would reduce horsepower slightly because it'll take a tad longer for the spark to actually ignite the air+fuel mix. My lawnmower specifically states to use 87 only - it won't run very well on high octane fuel because it doesn't have the spark energy to ignite that stuff.

 

mike c.

[strang3majik]

So, what about in the event of a N/A engine that has a very high compression? Say, 20-30 lbs higher in every cylinder compared to spec?

Would a higher octane be better for it? Seeing as it could be a change in the Comp-Ratio?

 

yes, run high test if you have higher compression.

 

I think its safe to say, anywhere around 10:1 or higher you should probably run premium in.

 

The thing I don't understand is, my 98 Ram SS/T has a 360 with the hi-po computer stock and all, it says run regular.

We had a 98 Jeep Grand Cherokee 5.9 (360), and it said premium fuel only, with, what I'm assuming is the same computer. I know it has the same compression ration of 9.6:1, so, I have no idea what the difference is.

But, I've put premium in that before and haven't noticed a difference at all. Just that ethanol makes my gas mileage suck is all I've learned.

[spoolinturbo]

on my trip I used 87, 89, 91, 93 and 94. I will tell you mpg there was no difference. But if I used 87 I had wayyyyy less power going up hills that is fact because I tried it twice