[JJC]

The discussions in this forum about gas mileage reminded me of something my Jetta mechanic--who was a great mechanis--told me about 10 years ago when I owned VWs.

He said that he always put 93 octane (94 if he could find it) in his car, not because of the increased gas mileage, but because he felt it resulted in less wear and tear on the engine. Here was his reasoning: Higher octane is achieved by using a higher percentage of "branched chain" hydrocarbons in the gas compared to "straight chain" hydrocarbons (I know this part to be true as I am a chemist). When the gas ignites, the branched chain HCs don't burn or explode as quickly as straight chain, thus the ignition of branched chain HCs is more efficient (higher mileage) and easier on the engine (less explosive = less wear and tear on the pistons).

Does this make sense to anyone else or is pure hypothetical BS?

 

[Ry]

Use what's recommended for your car. Since this is in the 2002 forums, I'm assuming you have a 3rd Gen with the QR25. From b15sentra.net there's been some debate on which octane. I've heard the SE-R's say one thing while the manual says another.

 

[altypaul]

To put higher octane in you car than the manual suggests is a waste of money. Use 87, as recommended by Nissan for the 2.5 Altima. The only reason to go higher is if your engine knocks.

See this page for more info:

http://chemistry.about.com/library/weekly/aabyb100401.htm

 

[pvick]

Higher vs Lower octane fuel

I'm not being picky, but the fuel/air mix in your combustion chamber does not explode; it burns. If it exploded, you would have the remains of a once fine engine, which is close to what happens when detonation sets in.

Bottom line is what one respondent advised. Use what the manual tells you to use. If you use 93 octane when the engine is designed to run on 87, you will increase your mechanical compression ratio since more of the unburned gases will deposit themselves on the piston tops, heads, and valve faces. This will, in turn, require you to use a higher octane fuel.

PVick
2002 Alty, Silver, 214 CID V6, Manual tranny

 

[mUSiCiaN]

The Manual says Nissan recommends to use 93 octane on a 3.5 and 87 on 2.5, now I know the Max has the 3.5, does the Max recommend 93 octane also? anyone know?....$.10/gallon difference is alot in the long run even if it is only $1.10 for 93 octane name brand

 

[Ry]

The Manual says Nissan recommends to use 93 octane on a 3.5 and 87 on 2.5, now I know the Max has the 3.5, does the Max recommend 93 octane also? anyone know?....$.10/gallon difference is alot in the long run even if it is only $1.10 for 93 octane name brand

The Maxima requires premium fuel.

 

[Altimat]

An explosion is a very fast burn. For 12,000 miles per year at 24 m.p.g. the extra .10/gallon you pay for premium costs you $50 per year. Indulge yourself. Modern cars are able to adjust spark advance electronically enabling the engine to make additional power with higher octane fuels. Considering they burn cleaner, contain higher-guality additives and detergents, and also result in better mileage the cost is actually less than $50 per year.

 

[ThurzNite]

The Maxima requires premium fuel.

did u have a 1st gen or 2nd gen? did that require premium too?
Jay

 

[Afty]

1st through 3rg gen Maximas ran on regular fuel. 4th gen (with the VQ) was the first to require premium.

 

[Sassan]

I suggest you guys sent a private message to kenshi and to kierandill, and you will learn everything there is to know about gasoline octane.

 

[02alty driver]

the 3.5 needs the higher grade fuel due to it's high compression status but the 2.5, it's not really necessary and will not get you any better milage on the car, they tell you to put mid grade, go put midgrade it will probably be better off

 

[Ry]

did u have a 1st gen or 2nd gen? did that require premium too?
Jay

We've still got the 2nd gen Max. It's parked out front collecting dust. It didn't require premium.

 

[mUSiCiaN]

the 3.5 needs the higher grade fuel due to it's high compression status but the 2.5, it's not really necessary and will not get you any better milage on the car, they tell you to put mid grade, go put midgrade it will probably be better off

Careful of some of the mid grade fuels in the plains and midwest as they mix gasohol (corn) into there mid grades.....I lived in Nebraska and didnt realize that till I decided to read what I was pumping in at the Amoco

 

[altypaul]

Actually, doesn't it require 91 octane, rather than 93?

Around here premium is 20 cents higher than regular. We don't have 91 octane, but only 87, 89, and 93.

My brother has run nothing but regular in his 95 Maxima with no problems. He has over 200,000 miles on it and climbing. I don't recommend this, but thought I would share that anecdote.

The Manual says Nissan recommends to use 93 octane on a 3.5 and 87 on 2.5, now I know the Max has the 3.5, does the Max recommend 93 octane also? anyone know?....$.10/gallon difference is alot in the long run even if it is only $1.10 for 93 octane name brand

 

[BuchoGTP]

This was a post on the GP board: Hope it clears some stuff up

This is in the new C+D November issue.


They first do a really good job of explaining what knock is but Ill skip typing that.
They took a Dodge Ram with a 5.9L V8, a Honda 3.0LV6 Accord, and a Ford 4.6LV6 Mustang that all run on regular. Then they took a turbocharged Saab 2.3L V4 9-5 Aero and a BMW 3.2L V6 M3.

The first day they drained all the cars fuel tanks and filled them up with Mobile 87octane. The cars were driven for two days then taken to the track and for dyno testing.
The next day the tanks were drained again but this time filled with Mobile 91octane. Two days later they were taken to the track and dynod.

The Ram with premium tweaked out a few extra horses but track performance was the same. The Ram has a mechanical distributor and no knock sensor so the engine didn’t know what kind of gas it was getting.
The Mustangs, w/ premium, knock sensors picked up a change in fuel and picked up 2 more horses and shaved off .3 seconds in the 1/4mile.
The Accord w/ premium lost almost 3 horses. No one they talked to could explain why the Accord lost power. The Accord lost 1.5% in performance at the track.

Now the Aero running on regular lost 9.8% of its power, and performance at the track dropped 10.1%
Now here’s what’s interesting. C/D found out that the M3 cannot be dynod. When the front wheels of the M3 aren’t spinning at the same speed of the rear wheels, the engine wont rev over 6300RPM, peak power is at 7900. C/D called BMW and they said they did this because if the car isn’t moving fast enough not enough air will get into the radiator and the car will overheat and retard spark timing. At the track the M3’s performance decreased by 6.6%.

They finish off with saying that there is no compelling reason to switch to a higher octane fuel for cars that require regular. If cars that need high octane fuel are given low octane it will hurt performance. If the car is sophisticated enough the engine will adapt but may suffer problems in the near future. They say that if a car is knocking you should invest in a tune up and not bandage the problem by giving higher octane fuel.

Here's a link to the scanned article (off the contour board)

http://www.contour.org/cgi-ubb/ultimatebb.cgi?ubb=get_topic&f=1&t=009793

 

[kenshi]

It's really so simple. Gasoline with a high octane rating ignites at a higher temperature. There's really no other difference. You use gasoline with a high octane rating when you don't want the gasoline to ignite in the cylinder before the spark plug fires.

 

[BuchoGTP]

Exactly, so unless you're experiencing detonation (knock or ping), there's no point putting higher octane in your car than recommended. You're most likely going to experience knock when:
the outside temp is high, you have an S/C or T/C, your engine has V. High mileage, or you have a high compression ratio and a heavy foot.

 

[pvick]

To BuchoGTP;

Excellent letter. I concur with the results of the tests you shared. In '95, I took a 430 mile trip in a '94 Accord EX (4-cylinder, 8.8:1 compression ratio). I started the trip with a full tank of 93 octane Amoco. I noted there was a drop in fuel economy and a distinct lack of power when passing other cars on two-lane roads. I have taken the same trip over 55 times so I am familiar with the road and vehicle performance. I contended that with an 8.8:1 mechanical compression ratio, the hiher octane (which is formulated to have a slower, more controlled burn rate), the engine was not able to take as full advantage of each cylinder of fuel/air mix it was receiving.

Some years before, I had an '88 Mustang LX with the 302CID V8 and noted something interesting. In the winter in the area in which I was living then, gasoline was oxygenated with benzene to supposedly reduce contaminates when engines were cold. Apparently, the ozygen sensors in the Mustang read the exhaust as having a lean mixture (system was speed density and not mass air) and increased the fuel delivery to the injectors. The result was a noticeable increase in power with a 14% decrease in gas mileage.


Paul V
2002 Alty
Silver/Charcoal
214CID V6
Manual Trans

 

[wild willy]

Just a foot note

To BuchoGTP;

Excellent letter. I concur with the results of the tests you shared. In '95, I took a 430 mile trip in a '94 Accord EX (4-cylinder, 8.8:1 compression ratio). I started the trip with a full tank of 93 octane Amoco. I noted there was a drop in fuel economy and a distinct lack of power when passing other cars on two-lane roads. I have taken the same trip over 55 times so I am familiar with the road and vehicle performance. I contended that with an 8.8:1 mechanical compression ratio, the hiher octane (which is formulated to have a slower, more controlled burn rate), the engine was not able to take as full advantage of each cylinder of fuel/air mix it was receiving.

Some years before, I had an '88 Mustang LX with the 302CID V8 and noted something interesting. In the winter in the area in which I was living then, gasoline was oxygenated with benzene to supposedly reduce contaminates when engines were cold. Apparently, the ozygen sensors in the Mustang read the exhaust as having a lean mixture (system was speed density and not mass air) and increased the fuel delivery to the injectors. The result was a noticeable increase in power with a 14% decrease in gas mileage.


Paul V
2002 Alty
Silver/Charcoal
214CID V6
Manual Trans

Fords, on the whole, suck. I know, i have owned 5 or so, the latest beiing a 99 Explorer, which i traded on my 3.5. I had 10,000 miles on it only because i hated driving it.

 

[pvick]

Wild Willy;

Actually, I have to tell you the '88 Mustang I owned was the most reliable car I have ever had. That includes Toyotas and Hondas, too.

Paul V
2002 Alty SE
Silver/Charcoal
214CID V6
Manual Trans