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View Full Version : High Octane vs. Regular


LakePirate
10-07-2005, 12:08 PM
So I am riding down the road the other day looking at gas prices and it dawns on me....Do the benefits of running high octane outweigh the drawbacks of the high price?

Not being a math major please bear with me.

In the good ol' days when gas was around a dollar the percentage mark up for 93 over 89 was about 16.68% (0.999 to 1.199)

When it went to two dollars the mark up was 9.1% (1.999 to 2.199)

Now with it at three dollars the mark up is 6.25% (2.999 to 3.199)

Well what does that mean?

Let's say that you get 15 miles per gallon when you run regular, to get the mpg benefit of running 93 you would have to see an improvement to 18 mpg to make it worth at a dollar. Probably not going to happen.

Now at the 3 dollar rate, if you get 15 mpg and it increases 1 mpg to run 93 it is a push, you pay the same. The increased gas mileage is the same as the increase in price.

But, if you get better than 1 mpg difference because of running 93 as opposed to running 87 then you are actually saving money.

While these gains are not huge, it is something to look at. 15 mpg is the break even point, if you are getting less, then the cost savings would be greater. If you are getting more mpg then you will have to see greater gains in mileage to get the benefit.

On top of that, in theory you get less build up on you fuel injectors and the engine performs better. Thus leading to fewer repairs and greater savings for the long haul.

Any thoughts?

3event
10-07-2005, 12:19 PM
Hadn't thought of that, it's a good question. Left an email msg for a friend who's an engineer at BP Amoco to get the company line on that. Their website claims fuel economy is most affected by running premium in a new car and preventing deposits / fouling from decreasing mileage over time.

But as with all such claims there is no data presented to back this up. I've never heard of any real data on this subject....

In our cars, I've been running 87 for the savings and dump in fuel injector cleaner every couple months..... food for thought though....

LakePirate
10-07-2005, 12:39 PM
Well as I am out researching this topic on the web the FTC says that an increase in octane will not increase your gas mileage and that there is no benefit other than stopping knocking. Others say that it will not increase the performance equal to the cost. Well, that is no longer the case.

When I have made road trips in the past I have burned high octane and gotten better mileage than I did when I burned regular on road trips. Don't really know around town.

I am going to run it for a week or two and see what happens.

east tx skier
10-07-2005, 01:04 PM
In both my cars, (Ford Expedition and Honda Accord), I was told not to run anything but 87. I don't know that I'd get an increase in mileage. The Honda is rated for 86 Octane. 87 is a treat for it.

ryanbush
10-07-2005, 02:03 PM
GM reccommends not running anything above 87 in their cars, except a few of the performance models. the higher octane gas causes carbon build up on the pistons.

Hoff1
10-07-2005, 03:18 PM
Being an engineer, Iíve actually questioned this before and did a little comparison in EXCEL. I was looking for when the $/mile gets cheaper. My Jeep says to use 87 unless I plan on towing for an extended distance. Then it says to use 93. Premium in my area is always $0.20 more per gallon since I started driving 12 years ago.

It all depends on how much premium improves your gas mileage. Can be based off of a percentage. Here's a chart I put together to show when it becomes cost effective depending on your gas mileage increase based on percentage.
Sorry about this, I'm letting my nerd come out.

PendO
10-07-2005, 03:24 PM
Being an engineer, Iíve actually questioned this before and did a little comparison in EXCEL. I was looking for when the $/mile gets cheaper. My Jeep says to use 87 unless I plan on towing for an extended distance. Then it says to use 93. Premium in my area is always $0.20 more per gallon since I started driving 12 years ago.

It all depends on how much premium improves your gas mileage. Can be based off of a percentage. Here's a chart I put together to show when it becomes cost effective depending on your gas mileage increase based on percentage.
Sorry about this, I'm letting my nerd come out.

I'm a bit confused on the Y axis ... where is the break even point?

Also, when % increase is 0, what is the Y axis telling me?

Thanks man, its been a few years since I had to plot points.

bcampbe7
10-07-2005, 03:27 PM
Being an engineer, Iíve actually questioned this before and did a little comparison in EXCEL. I was looking for when the $/mile gets cheaper. My Jeep says to use 87 unless I plan on towing for an extended distance. Then it says to use 93. Premium in my area is always $0.20 more per gallon since I started driving 12 years ago.

It all depends on how much premium improves your gas mileage. Can be based off of a percentage. Here's a chart I put together to show when it becomes cost effective depending on your gas mileage increase based on percentage.
Sorry about this, I'm letting my nerd come out.


Can you explain that a bit more for us "slow" folks?
It's Friday afternoon and you are expecting entirely too much from us. :D

Footin
10-07-2005, 03:29 PM
Call me a pesimist, but I do not think running a higher octane will get you better gas mileage.

PendO
10-07-2005, 03:31 PM
Call me a pesimist, but I do not think running a higher octane will get you better gas mileage.

I'd agree, at least from the experience with my Ford Exploder, if I run higher than it calls for the only one doing better is the owner of the pump/gas ...

AirJunky
10-07-2005, 03:31 PM
Call me a pesimist, but I do not think running a higher octane will get you better gas mileage.
Ever tried it? I haven't, but it's tempting. A 10% increase isn't much. If your getting 15 mpg with regular, then get 17 mpg with premium, it pays off.

east tx skier
10-07-2005, 03:37 PM
The way I always understood it (bear in mind I'm an English major) is that you are best off running what's recommended for your engine. If your application requires 93, then running 87 will lead to inferior performance, ergo, fewer miles per gallon. But with a car that is set up for 87, why would 93 get you better mileage.

PendO
10-07-2005, 03:37 PM
Ever tried it? I haven't, but it's tempting. A 10% increase isn't much. If your getting 15 mpg with regular, then get 17 mpg with premium, it pays off.

I tried it with the ford, although I was not driving the exact same 300+ miles ... it "seemed" that I actually did better with the cheaper/called for gas ... also, proper air pressure in the tires is a big deal, especially with the cooler temps, people may want to make sure they have enought PSI in there ... gawd I really should slide over to my work computer!

Hoff1
10-07-2005, 04:01 PM
Sorry for the incomplete explanation on the chart. The percentage on the x-axis is how much gas increase you expect with premium. I plotted this as a variable to let everyone try there own experiements (my experiments indicate 2%-7% on the highway but definitely varies). The y-axis is the cost of regular gas. The line on the chart separates the good idea / bad idea. If you know what increase you expect, the point must be above the line for it to pay off. I.e., if you get 8% increase, it wonít be cost effective until gas is over $2.50/gallon. If you expect 10% increase, then $2.00/gal is where it becomes cost effective (10% increase in gas cost).

Or to make it real simple, your increase in gas efficiency has to be larger than the increase in cost from regular to premium.

I know itís Friday when Iím working very hard at anything but work.

gimmemoedmb
10-07-2005, 04:37 PM
I took an internal combustion engines course in college a couple years ago and the prof said the only thing the octane means is the resistance to combustion. You use higher octane in higher compression engines to prevent knocking. The higher octane is just harder to ignite so you would actually have more carbon buildup with the higher octane. As far as I know, you get no increase in mpg or really any other benefit from higher octane unless you get knocking with 87. Someone please correct me if I'm wrong.

tommcat
10-07-2005, 05:42 PM
not only will you not get better fuel mileage with super, you will actually get worse MPG and harder starting if your vehicle does not call for it. if your owners manual says to use 87, then that is what you should be using.
i dont know how many of my customers i've had to tell this to.
use what your car, truck, boat, sled calls for!

wakesport
10-07-2005, 05:42 PM
This was the same thing I learned in IC engines class when I was an engineering student in the 70's. I don't think the purpose of higher octane fuel has changed.

Foiler
10-07-2005, 06:47 PM
Oh Yea, well when I worked for NASA......J/K

PendO
10-07-2005, 06:52 PM
not only will you not get better fuel mileage with super, you will actually get worse MPG and harder starting if your vehicle does not call for it. if your owners manual says to use 87, then that is what you should be using.
i dont know how many of my customers i've had to tell this to.
use what your car, truck, boat, sled calls for!

Its tantamout to giving your friends the wrong brand of beer IMO. More expensive does not necessarily means it tastes better ... plus, for people like myself high end beer is just a waste of time ... there is a reason microbrew's are just that, "micro" ... if the appealled to they masses they would be "macro" and they too would have hot chicks on billboards:)

Bud, Bud Light, Coors ... and Kokanee!!!! Ever spot the sasquatch on the Kokanee label? Usually it is on the far right side of the moutain - not one on this label.

JimN
10-07-2005, 07:37 PM
As was mentioned before, higher octane doesn't burn the same as low octane. Low octane will burn faster and with lower compression. High compression motors need high octane so the detonation isn't an issue. The fuel needs to burn at the right time and at the correct rate. Using high octane in a low compression motor will not help get better mileage and I haven't heard that it helps run cleaner since all gas is supposed to have detergents in the mix. If the vehicle is used hard in a hot, dry climate, detonation is more likely to occur. If this happens, higher octane helps.

Using high octane on a trip isn't really an objective way to find out if the mileage will be different since day-to-day driving includes stop and go, while going on a trip usually involves a completely different driving style.

Basically, it's best to use what the manufacturer recommends unless the motor has major carbon deposits or the timing has gone out of adjustment, in which case that needs to be addressed separately.

6ballsisall
10-07-2005, 09:11 PM
Read owners manuals in most cars. Most newer cars clearly alude to the fact that you are wasting your money running high octane fuel in your car. (except for Mercedes, and Hi-Po cars, etc...) There are actually theories out there that burning high octane fuel in a standard engine for long periods of time can actually damage an engine as it doesn't burn hot enough and can cause internal issues.

JimN
10-07-2005, 09:52 PM
The issue of not burning hot enough is a good one. The only way the in-cylinder temperatures will be high enough is with enough compression, correct spark/valve timing and the proper octane. A low compression motor will not burn the fuel completely if the fuel burns too slowly (high octane). Think about the way a diesel engine works- the glow plug only stays on till the in-cylinder temperature reaches a certain point, then it's turned off. The fuel/air mixture burns just because the compression, octane and temperature in the cylinder are correct, even though there is no ongoing source of spark.

6ballsisall
10-07-2005, 09:56 PM
The issue of not burning hot enough is a good one. The only way the in-cylinder temperatures will be high enough is with enough compression, correct spark/valve timing and the proper octane. A low compression motor will not burn the fuel completely if the fuel burns too slowly (high octane). Think about the way a diesel engine works- the glow plug only stays on till the in-cylinder temperature reaches a certain point, then it's turned off. The fuel/air mixture burns just because the compression, octane and temperature in the cylinder are correct, even though there is no ongoing source of spark.

So basically cylinder washdown?

PointTaken
10-07-2005, 09:58 PM
So basically cylinder washdown?
All said and done, is it this? Just run what the manual says to run? :confused:

6ballsisall
10-07-2005, 10:00 PM
All said and done, is it this? Just run what the manual says to run? :confused:

Tru dat tru dat, if the manufacturer says you don't need it its all good brutha http://deephousepage.com/smilies/afro.gif

JimN
10-07-2005, 11:00 PM
The car manufacturers do a ridiculous amount of testing on their motors and cars. This doesn't eliminate real world problems, but all they can do is approximate what will happen once the vehicle leaves the dealership. The correct fuel/air mixture for a balance of power/economy/service life has been known for a long time. This is assuming no changes in fuel or damage to the motor occur. They have tested their motors with good and bad gas of all grades. There's no reason to use premium if the manual calls for regular. There are vehicles out there that have gone to the moon and back in terms of mileage without using premium. Why pay the extra $ when it won't do any good?

Workin' 4 Toys
10-08-2005, 12:07 AM
Diesel premium. Oh wait, mid grade, or regular? Ah, nevermind, its all just the left over garbage at the bottom of the old petrol tanks anyway.

87 oct all the way around here.(except the sleds when ever possible)

Ever notice the racing fuel has not gone up much? 110 here used to be about $4.50 a gallon when I ran it in the GTO and others. I looked at the 110 pump last week and it was about $4.85. A difference of $0.35 a gallon in ten years. Maybe I did not see the 1 in front of the 4...?!?!:confused:

ryanbush
10-08-2005, 01:44 AM
Diesel premium. Oh wait, mid grade, or regular? Ah, nevermind, its all just the left over garbage at the bottom of the old petrol tanks anyway.

87 oct all the way around here.(except the sleds when ever possible)

Ever notice the racing fuel has not gone up much? 110 here used to be about $4.50 a gallon when I ran it in the GTO and others. I looked at the 110 pump last week and it was about $4.85. A difference of $0.35 a gallon in ten years. Maybe I did not see the 1 in front of the 4...?!?!:confused:

I run 101 in the vettes, and my bike. it was 2.85 and the end of last summer and when I filled up last week it was 4.29 at the pump. a buddy of mine who has a go fast boat with twin blown engines runs 107 in his boat and says that it is only 3.25 at the oil company. so I may have to go down there next time and see what they have to offer