# question about octane rating



## 97sentragxe (Jun 20, 2002)

Since theres been so much talk lately about gasolines, mothballs, etc. I myself have a question:
At a Sunoco station near my house, I noticed that they have gas with an 86 octane rating. It's significantly cheaper than regular 87 octane (10 cents per gallon) and with it being only one point lower than 87, I just wonder if this could be used in my fuel system with no negative side effects. So far, I've used only 87 octane every time I've gotten gas, except one time when the 87 octane pump was broken, I put some 89 octane in. (My car was TONS faster, too with that better gas.  ) Anyway, I assume this 86 octane would be okay for a Sentra, since a car cannot be much more of an econobox that a Sentra, but since I'm near a lake, could this stuff be meant more for things like boats, jetskis, and starting campfires? 
Thanks for help.


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## ccroaddog (Jun 20, 2002)

if your car is a lot faster with 89 octane dont you think it may be a little slower with 86 octane? Besides im pretty sure that your vehicle requires 87 octane and shouldnt go any lower. Just spend the extra 10 cents


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## bahearn (Jul 15, 2002)

If your car was really "tons" faster, then your timing is being retarded when using 87-octane. If 89-octane really was faster, you'd notice an improvement in gas mileage, too. So, if 87-octane requires the ECU to retard timing, 86-octane would require even *more* timing retard. Less power, lower mileage. If the lower grade is 7% less cost, you need to get at least 7% better gas mileage with the higher grade to make the economics work for using 87-octane. Of course, if your SOTP dyno can't stand the power loss, who cares about economics.


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## 97sentragxe (Jun 20, 2002)

I figured the  would be obvious enough, but I guess not. No, my car was NOT faster at all when I used the 89 octane gas, I said that to make fun of those people who think that putting "better" gas in their car will make them a lot faster.


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## vrux (May 13, 2002)

Actually, in SCC October 2002 issue the '03 Nissan 350Z made an additional 5 hp and 2 lb-ft of torque at the wheels on the dyno when going from 91 octane to 100 octane.


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## Scott (Apr 15, 2002)

vrux said:


> *Actually, in SCC October 2002 issue the '03 Nissan 350Z made an additional 5 hp and 2 lb-ft of torque at the wheels on the dyno when going from 91 octane to 100 octane. *


Well, the 350Z was designed for premium fuel. 

*edit* Right, because of knock(see my post) - Pat


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## PatScottAKA99XE (Apr 30, 2002)

Octane rating: The fuels ability to resist knock( ping)
The higer the ratting the more knock resistant it is. Just about every owners manual I have seen give a minimum suggested octane. Dont go below it.

FYI, the higher the octane, the slower it burns.

If your car is designed for 87, putting in a higer octane will not make it faster. It only works if you have mods that tend to increase the chance of knock.


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## Guest (Aug 27, 2002)

higher octane fuel means less knocking!! if higher octane fuel id 10cents more go for it. better in the long run


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## Scott (Apr 15, 2002)

KdudL said:


> *higher octane fuel means less knocking!! if higher octane fuel id 10cents more go for it. better in the long run *


Higher octane fuel is only better if it's required for your car. Unless you're running timing more advanced than the factory specs for 87 octane fuel, turbo, or nitrous you're just wasting the 10 cents per gallon.


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## NismoPC (Jul 28, 2002)

97sentragxe said:


> *I said that to make fun of those people who think that putting "better" gas in their car will make them a lot faster. *


As everyone is stating, higher octane in some cases will increase the performance of your car, but too high of an octane could be a waste of money. This is esepcially true, as everyone has stated, when you advance your timing.

Don't go below recommended fuel specs. Those are the most conservative specs for fule rating.


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## bahearn (Jul 15, 2002)

> FYI, the higher the octane, the slower it burns.


Technically, that's not true, but it will suffice for the discussion at hand.


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## 97sentragxe (Jun 20, 2002)

Hmm.. Maybe 89 octane would be fine, then. Kind of a mix between "bare minimum" and "ridiculous excess"


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## Guest (Aug 27, 2002)

I run nothing but 93 octane in my 96 SE-R. Wasting money - no. With the mods I have, timing I've bumped up, etc. the car runs like a brick when I put even 89 in it.

Plus, I have had fewer EGR problems that some of my other SR20 friends. But, that could just be luck. Or maybe not...


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## 97PocketRocket (Jul 31, 2002)

It also tends to be better for the engine to run higher octane if you live in extreme heat areas, (avg 100+ degrees F) as the external heat obviously makes the car run hotter which in turn tends to make the car more susceptable to knock...likewise, if you drive in high temp areas in a lot of stop and go (you'll most likely tend to have the a/c on in this situation too which makes it even worse), higher octane will tend to benefit as well, you may not see gas mileage increases but you will help lengthen the life of your car's engine. This actually holds true for just about any car despite what the manual says. Octane tends to follow your driving tendancies and needs and is more importantly based on additional heat generating components/mods like everyone else has mentioned.


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## bahearn (Jul 15, 2002)

Any heat input into an engine ups its octane requirement, whether it be intake air, fuel, coolant, etc. I don't know the magnitude increase in octane requirement for a given input; time to retrieve my copy of "Internal Combustion Engines in Theory and Practice, Vol 2.".


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## 97sentragxe (Jun 20, 2002)

I'm all stock though, and drive 99% on the highway at 65 mph. It hardly ever goes above 100 degrees here, either. I dunno, I'll probably just stick with the same 87 that I've been using all the time.


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## Guest (Aug 28, 2002)

And you'll probably be fine. I know my ECU starts wussing my SR20 out if I run anything less than 89.


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## azkicker0027 (May 31, 2002)

i religously put NOS octane booster with every tankful, since also that i advanced my timing to an exact 15 degrees, and run on 93 octane fuel, all the time, and yep, the "off-road" formula......


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## Guest (Aug 28, 2002)

azkicker?

You following me around tonight?


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## Teknokid (Jun 1, 2002)

Higher Octane does give you better fuel mileage. If i run 87 octane, i will barely hit 300 miles on one tank. If I get 91 octane, i get about 360-390


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## azkicker0027 (May 31, 2002)

follow what?? huh?? me no understand..............oh i see, you also run 93, ok, gotcha........


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