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Harley Polly
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Discussion Starter · #1 ·
Hi everyone,

I was wondering what octane level that you are burning in your 3.5 SEs. The book recommends 91 but also states that you can run it on 87 grade if premium is unavailable. In Canada, our Transport Ministry rates fuel economy for all new cars and they tested the Altima 3.5 with regular 87 grade. The price differential between 87 and 91 is 40 cents per gallon.

My last car, a Mazda 929 did 160,000 troublefree miles on regular with "premium recommended". I have tried all grades in my 3.5 and am hard pressed to find any advantage to using hi test.

Your comments are appreciated.

Pierre
 

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The engine will run just fine on 87 octane, but you will be sacrificing torque, and probably a little gas mileage. Since 91 (or better yet 93) octane gas burns slower than 87, it allows the engine to run more advance (less retard) to avoid pre-ignition (ping or knock). Since the engine is one with a high compression ratio, it is worthwhile to use the highest octane gas you can find.

But if you don't mind taking the performance hit, and the gas mileage doesn't suffer too much, than you should be fine. BUT, if that's true, why didn't you just buy the 2.5 instead?

I only wish I could get better than 91 octane that they serve us in CA.

BTW, $0.40 extra a gallon is ever greater extortion than around where I live. Even in CA, with our "special" low emissions gas, it only costs about $0.03 more to produce higher octane gas. Is that all stations? Or just the ones near you (the premium for premium tends to run higher in affluent neighborhoods).

Of course, my favorite is the Full serve stations. Usually there is about a $0.20-0.30 difference between the two grades at self serve, but at full-serve, there often is only a $0.05 difference, if that.
 

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Davard said:
The engine will run just fine on 87 octane, but you will be sacrificing torque, and probably a little gas mileage. Since 91 (or better yet 93) octane gas burns slower than 87, it allows the engine to run more advance (less retard) to avoid pre-ignition (ping or knock). Since the engine is one with a high compression ratio, it is worthwhile to use the highest octane gas you can find.

But if you don't mind taking the performance hit, and the gas mileage doesn't suffer too much, than you should be fine. BUT, if that's true, why didn't you just buy the 2.5 instead?

I only wish I could get better than 91 octane that they serve us in CA.

BTW, $0.40 extra a gallon is ever greater extortion than around where I live. Even in CA, with our "special" low emissions gas, it only costs about $0.03 more to produce higher octane gas. Is that all stations? Or just the ones near you (the premium for premium tends to run higher in affluent neighborhoods).

Of course, my favorite is the Full serve stations. Usually there is about a $0.20-0.30 difference between the two grades at self serve, but at full-serve, there often is only a $0.05 difference, if that.
I took a roadtrip this summer from CA to CO--91 octane was the highest grade fuel at every single station I visited....grubble!!!
 

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Harley Polly
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Discussion Starter · #4 · (Edited)
Hi Dave,

Thanks for the response. Unfortunately this forty cent differential is pretty much the norm from coast to coast in Canada. I guess what I could do would be to run a tank of lo test and one of hi test, check the mileage for each and do a cost per mile. If I have to use premium, then I will. Just what I need, another project! Bye for now.

Pierre
 

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I use 93 octane gas. Every time I fill up is around $25, and I usually fill long before the needle hits empty. The MPG calculator on my car is screwed up I think, it's always stuck on ~18.8 miles per gallon :angry2:
 

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Snow White 3.5 SE
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premium baby
 

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Former Alty Owner
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fatboy said:
I use 93 octane gas. Every time I fill up is around $25, and I usually fill long before the needle hits empty. The MPG calculator on my car is screwed up I think, it's always stuck on ~18.8 miles per gallon :angry2:
Fatboy.. you need to reset your MPG everytime you fill up.. otherwise it will just continue since the last time you reset. Same thing with your MPH and TRIP.
 

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scottlny said:


Fatboy.. you need to reset your MPG everytime you fill up.. otherwise it will just continue since the last time you reset. Same thing with your MPH and TRIP.
LOL. No wonder!! Thanks scott, I always assumed it recalculated every couple minutes or miles. The MPH was always the same too :p
 

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There is no difference in combustion speed among 87-89-92-94 octane graded fuel. Higher octane doesn't equate to better performance either. Lead boost is another matter. Just that the fuel with the higher numbers are more stable at higher temps and the engine can run at a more advanced spark time. Hence when HO fuel is introduced to the chambers, there is less likelihood of fuel igniting before all the valves are closed (this is where the ping comes from). The higher the compression ratio of the engine the hotter the exhaust gasses are and as well the hotter the chamber when the exhaust gasses are evacuated. The engine responds to pre-ignition by delaying the spark time. It works but only to prevent engine knock. The performance may suffer but not necessarily under conditions when the engine is NOT stressed. If you're not fouling your plugs and the emmissions read within normal parameters then you should be okay until your engine ages and you may need to go back to the recomended fuel. That's another story.

I don't know all the reasons why the engineers recommend higher octane. I would just as well keep to it for warranty puposes. No questions, no argument.
 

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I was just at the gas station and the gas went from 87 $1.48, 89 $1.59, 93 $1.69 but in Jersey it's 20cents less for each one so putting 93 in it in Jersey is the same price as 87 in NY, so I fill up in NJ
 

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virtuoso1 said:
There is no difference in combustion speed among 87-89-92-94 octane graded fuel. Higher octane doesn't equate to better performance either. Lead boost is another matter. Just that the fuel with the higher numbers are more stable at higher temps and the engine can run at a more advanced spark time. Hence when HO fuel is introduced to the chambers, there is less likelihood of fuel igniting before all the valves are closed (this is where the ping comes from). The higher the compression ratio of the engine the hotter the exhaust gasses are and as well the hotter the chamber when the exhaust gasses are evacuated. The engine responds to pre-ignition by delaying the spark time. It works but only to prevent engine knock. The performance may suffer but not necessarily under conditions when the engine is NOT stressed. If you're not fouling your plugs and the emmissions read within normal parameters then you should be okay until your engine ages and you may need to go back to the recomended fuel. That's another story.

I don't know all the reasons why the engineers recommend higher octane. I would just as well keep to it for warranty puposes. No questions, no argument.
Umm, Sorry.

Higher octane fuel burns more slowly, if everything else is equal (if you raise the compression, then the conditions aren't equal... the pressures and temperatures are higher). It also resists spontaneous combustion (igniting from high temperatures or hot spots) better. The reason that you shouldn't run high octane gas in a car designed for lower octane is that the higher octane gas doesn't have a chance to burn as completely in a car tuned for low octane gas (unless timing is advanced), and therefore you need a greater throttle input for a given load, you get less mileage and produce more emissions (or wear out your catalyst faster).

And higher compression results in higher temperatures during the compression stroke (think how a diesel works). Higher octane gas is required to prevent precombustion related to these higher temperatures and pressures. And the exhaust temperature is not necessarily higher. There are an unbelieveable number of variables that determine exhaust temperature, and usually it is the engineer who works it out (for emissions reasons). Ideally, you would have low temps (meaning that more of the energy in the gas made it to the crank), but that would be bad for emissions (unless you had utterly complete combustion and all that was output was CO2 and H20).

Now just for trivia, Honda discovered that at really high RPMs (over 13k or so) and pressures, precombustion wasn't a problem, and the events were happening too fast for preignition to matter.
 

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Pierre Garneau said:
Hi everyone,

I was wondering what octane level that you are burning in your 3.5 SEs. The book recommends 91 but also states that you can run it on 87 grade if premium is unavailable. In Canada, our Transport Ministry rates fuel economy for all new cars and they tested the Altima 3.5 with regular 87 grade. The price differential between 87 and 91 is 40 cents per gallon.

My last car, a Mazda 929 did 160,000 troublefree miles on regular with "premium recommended". I have tried all grades in my 3.5 and am hard pressed to find any advantage to using hi test.

Your comments are appreciated.

Pierre
Only Premium.. Anywhere from 91 to 94 here in Chicagoland.
 

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I believe the parameter to the question is: what would be the effect of using lower octane in the Altima. It's a question between a few Octane numbers. We're not talking about 100 octane. We're looking at where a 2 point differential in octane is hardly enough to remap timing.
 

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PS: I believe that fuel burn speed is related to fuel blend as opposed to the actual octane number (MON or RON etc). From what my engineer tells me, is that the burn speed may be related to octane rating in PUMP fuel only, because that's the way the fuel is formulated for whatever reason. He (the engineer) orders his ELF fuel and he gets it reblended according to his specs (which he won't divulge). But he can freely alter burn speed to a certain degree. Davard's argument made too much sense so I had to research it. Hey, even this old dog can learn new tricks.
 
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