Wow. Some people can't read.

Let me translate the sticker for you. It says that you should use at least 91 octane. Period. You can use 87 if you want, but you should use 91 or greater.

"For best performance" doesn't just mean horsepower. It means smoothness and fuel economy too. I think that's pretty self-explanatory.

On the other hand, our engines aren't exactly the most sophisticated things in the world, so I can see how they might be more sensitive to low octane than the more modern sophisticated ones. Still, here's a great case-in-point: The local BMW dealers here ONLY EVER USE ONE GAS in their cars, and that's Sunoco 94. Period. Regardless of price. That's gotta say something.

Also, I wonder how the wording of this bit seems to have eluded people:

In other words, no damage is done -- which is true -- and, to most people, the performance difference isn't noticed. Doesn't say there isn't a difference... just that there isn't one that people notice. I dunno about you all, but given how most people are, it seems perfectly reasonable to me that they don't notice a few hp and 1-2 mpg.

 

I guess the article in Cars.Com just didn't register with some. Yes, you can use 87 octane in a pinch, but for how long can your engine stand to be pinched?

See.. it is just like you can use Ibuprofin if you cannot get hold of Vicodin for your injured back.

Sure...

For me, the bottom line is that my car runs great on high-test and crappy on low-test. I guess that means something must be terribly wrong with my car, even though it screams just the way it is.

I will stop putting 93 octane in my Infiniti when they pry my cold, dead hands off the gas pump.

 

This does not make sense from a physics standpoint. Engines that run lean, run hotter; engines that run rich, run cooler -- with a rich fuel mixture there is more fuel to evaporate and cool the engine.

If you want to know more about Octane and what it means, then read all of my posts on this thread, on this site:
http://forums.maxima.org/showthread....6&page=1&pp=30
There you will find out that Octane requirements are dictated by the following three engine operating factors:
- Cylinder Pressure,
- Spark Advance, and
- Engine Temperature.
All other factors that any "expert" mentions, will ultimately turn out to impact one or more of these factors. That is why a rich mixture cooling the engine is important -- a cooler engine needs less octane.

The 04 Maxima has a 10.3 to 1 compression ratio and "recommends" premium while the 04 Accord has a 10.0 to 1 compression ratio and "recommends" regular. The Maxima says you can run regular, but recommends premium for better performance.

There are so many experts out there, its hard to know who to believe. When discussing "modern engine technology" (the VQ engine and the Accord engine among a few engines available) I can only speak about my experiences with my 04 SE, and I run 85 octane at 6K feet elevation. Read post #6 on my Octane thread (cited above) to find out why this is equivalent to 91 octane at sea level.

When I go east, I buy either 87 or 89 octane. On two occasions in the east I've tried three tanks in a row of 93 octane, and the performance seems to be marginally better, but then I rarely go WOT on my Max. If you do that consistently, you definitely should use 91-93. As for mileage, there were too many other factors occuring (head winds, Smokey Mts, etc) to make any difinitive statements about better mileage with 87 vs 93.

Finally, from what I know, all of Stephen Max's posts on this topic are correct.

 

Exactly my point. Low octane won't hurt the engine, but it will make a difference in performance (i.e. power, fuel economy, smoothness) that most people with "normal" driving habits won't even notice.

That's the key. If you drive like everyone else, go ahead and use the lower octane. The Maxima is an "everyone else" car, and it's built to take it. If you drive hard, or expect your car to run its best all the time, cough up the extra few bucks and use premium.

 

I agree with most of your points except smoothness and fuel economy. The use of regular does not make my Max run any less smooth. In the days before "modern engine technology," the accepted engineering advice to get the best mileage was to burn the lowest octane gasoline that did not cause knocking. With the newer technology, I'm just not certain if this advice is still appropriate -- but it may be. Note what Nissan says in their 04 owners Manual: "However, now and then you may notice light spark knock for a short time while accelerating or driving up hills. This is not a cause for concern; because you get the greatest fuel benefit {read 'efficiency'} when there is light spark knock for a short time under heavy engine load." Higher efficiency generally means better gasoline mileage and when you are very close to getting light spark knock, the engine is apparently at its most efficient. This was engine lab 101 for Mechanical Engineers before modern engine technology. What Maxima says may well mean that it still applies.

You will note in all of my earlier posts on the topic of Octane, I contunually stress that if you are racing, doing a dyno test, or regularly drive at or near WOT (Wide Open Throttle), you should certainly burn Premium. So we are in agreement there.

As to the point made by others that burning regular will cause your spark advance control to fail, there is no scientific evidence that this happens. However, if you have consistently burned premium in an older Max with high mileage and then burn regular, the abrupt change may cause a marginally performing control to fail.

 

SilverMax_04, I bet the reason we don't agree about fuel economy and smoothness is that I drive a 4th gen and you drive a 6th gen. The more primitive design as well as the higher mileage and age of my engine are probably big factors.

Whether high octane or low octane would be more efficient would, I would think, depend on the ignition system and oxygen delivery. Given a relatively weaker spark and/or less oxygen (high altitude, more restrictive exhaust, regional air composition), you'd want lower octane because it'd be easier to ignite and quicker to burn. Also, with less oxygen, high octane gas would make far less of a difference because the engine won't burn the fuel anyway. On the other hand, if you can make a big spark and deliver tons of oxygen, and have an ECU that can advance timings to the verge of knock, I don't see how you wouldn't get better mileage because combustion would still be quick and complete, but it would yield more energy. Either the engine will run leaner to save gas, or the driver will just spend less time on the accelerator.

Right?

 

Cough, gasp, I'm running out of air and oxygen!

The air is thinner here at 6K feet, but we can still breath and cars still run OK.

Remember my point about the three factors that influence octane requirement. At higher elevations the air pressure is less, so you need less octane. The advanced computer system (including Oxygen sensor) in the VQ (even in 4 Gen) compensates for the reduced oxygen in the thinner air. The 4 Gen VQ is not as sophistocated as the 6 th, but not by much. Back when your Max was new, the VQ was almost alone in having "advanced engine technology" in a production passenger vehicle. You may be correct about your higher mileage (and perhaps engine deposits developed over those miles) causing your engine to need higher octane gasoline. But don't blame the difference in technology -- there isn't much.

I'm not aware of my engine not burning the gasoline that the fuel injectors deliver to the engine because there is not enough oxygen to completely burn all of the fuel. If that were true, I would be diluting my engine oil with un-burned gasoline. Your arguments here are wrong for any car with computer controled ignition and an oxygen sensor.

Unless you have a turbo-charged engine, you will experience less power at higher altitudes because the oxygen in the air limits the ability to burn the gasoline. The fuel delivery system compensates for this and the result is less fuel to the engine and thus less power at altitude.

Once the spark occurs in a cylinder, the gas burns (regular or premium). The higher octane of premium does a better job of resisting pre-igintion (knock) before the spark occurs -- there is not much difference in buring after the spark.

The energy in a measured quantity of gasoline depends on its chemical composition, particularly the number of carbon atoms. Some premium gasolines are heavier that most regular gasolines and thus contain more energy per gallon -- but this is tough to measure and not a very big factor. The reduced number of carbon atoms in gasoline with 10% ethanol (the oxygen atoms in the ethanol replace some of the carbon atoms that would be in pure gasoline) is why many have been able to measure reduced mileage with this ethanol blend. Ethanol only has about 65% of the energy content of gasoline, so 10% ethanol will have about 6.5% less energy than straight gasoline. And don't let anyone fool you -- both with and without the extra oxygen in ethanol, the modern fuel delivery system compensates and produces complete combustion of either fuel. Oxygenated gasoline only helps reduce polution in cars made in the 70s or before oxygen sensors.

If you are suggesting that your older Max has "a relatively weaker spark" I suggest you have your ignition system repaired to improve the spark. It should be as good as a 6th Gen.

Hope this helps.

 

Do we have any definitive proof that "running on regular" for the entire life of a 91-octane recommened Max or I, does no harm?

Or, are we basically relying on hearsay and anecdotal reports?

I used to own a 1987 Toyota Tercel...a car with a whopping 105HP four cylinder that would not make it up a steep hill with the AC on. I had to use high-test for the entire 150,000 miles I drove it 'cause the freakin' four-banger would knock...no ping like a MF...on regular and midgrade!

...but the manual said "87 octane is recommended."

Ever since then, I no longer pay attention to car manual recommendations for gasoline.

If anyone wants to save money on their gasoline, do what I do -- drive less by riding in someone else's car as much as possible. On weekends, my girlfriend wants to take her whip instead of mine, which is just fine with me and my wallet.

 

No we don't. That is why I will, from time to time (but not too frequently), buy three tanks in a row of premium gasoline. I don't want the spark advance control on my VQ engine to only get used to running regular. I make it work, as it was designed to do.

But I will continue to burn mostly regular gasoline in my Max because it performs to my expectations -- and I never race the car and rarely call for WOT performance.

My girl-friend is my wife, and I end up buying the gasoline for her.