T800

I have been using Citgo. Always. I used Shell in Naperville/oakbrook (Chicago) area recently and the mileage dropped by about 3-4 miles per gallon. Then switched to BP(Amoco). Still it was low compared to the Citgo.

Not much difference in performance. Still got enough power in the wheels.

My other car (Civic) hates Shell too.

SilverMax_04

What a bunch of C-R-A-P.

Your Max was designed to provide maximum performance burning premium and to perform adequately burning regular. The Max is not a person, but a machine. It will perform based on how you ask it to perform. If you don't call for maximum performance (WOT), then you don't need the gasoline grade that costs more but will provide maximum performance when the Max is floored. Regular will work well in most circumstances.

If you abuse you Max by sloppily driving it hard, you can damage it. You can not damage the Max by burning regular (provided you do not get knocking when the engine is under load).

There is so much bad information out there about gasoline octane -- and no one wants to learn the facts -- they know what they know -- don't confuse them with facts. If you do want the facts -- go here:
http://forums.maxima.org/showthread.php?t=396716

Law520

So for those of us who just drive our Maxes casually everyday, regular unleaded or 87 octane is fine?

I like to treat my max about every 6 weeks to premium, and 'open it up' just to burn off crap in the engine. Have not had any problems or knocking with the engine.

SilverMax_04

Correct. It should perform adequately. Just don't get in a drag race and expect maximum performance from the VQ when it is burning regular. The spark timing will be somewhat retarded versus burning premium.

According to an engine expert on this site (SteVtec), it takes between 300 and 500 miles for the VQ's computer to completely recognize a gasoline octane change in your tank and adjust the spark timing accordingly. So an occasional tank of premium will only keep this system in a state of change. Suggest you pick one grade of gasoline and stick to that grade. If you do pick regular and later decide to go back to premium wait for this mileage before asking for Max performance.

MDS

According to Honda, their 3.5 liter Odyssey motor produces 244 hp on premium fuel and 211 hp on regular fuel. I’m sure Nissan’s technology is similar. The car’s computer will adjust its settings to run on lower octane fuel. You can do it, but you lose power and mileage.

SilverMax_04

You will lose power but not necessarily gasoline mileage. Remember the quote in my post above. The highest efficiency of a gasoline engine occurs when operating just short of pre-ignition. More likely to happen with regular than with premium gasoline. I now consistently run regular and earlier did tests running premium. I found that on the highway I got slightly better gasoline mileage with regular (acknowledging that there were many uncontrollable factors in these tests).

MDS

Hmmm, this is interesting. I welcome a difference of opinion. I was under the impression that higher octane fuel released more heat than lower octane fuel. Since our motors are heat transfer engines, more heat generates more power.

To maintain a certain speed, for example 60 mph, let’s assume the engine must produce 15 horsepower. To produce the required heat to generate 15 horsepower, it might take 9 drops of 87 octane fuel (per cylinder, per rpm) and only 8 drops 93 octane fuel. It takes more regular fuel because each drop releases less heat. The only way to generate the required amount of heat (power) with 87 octane fuel is to burn more fuel in the same timeframe. This relationship explains why fuel mileage decreases with lower octane fuel. This is especially true if the car’s computer can adjust its settings to take advantage of the higher octane fuel’s extra power.

SilverMax_04

Your premise is not necessarily correct. While some brands of premium gasoline contain more energy than some brands of regular gasoline, this is not a universal truth. The heavier the gasoline, the more energy it contains. When I worked for Amoco in the 70s and 80s, their premium gasoline (Amoco Super Premium) was blended with a high-octane component called "heavy ultriformate" which was heavier and higher in octane than other gasoline blending components. But not all refineries produce the same blending components and oil companies certainly don't all blend their gasoline the same way. While it is possible that premium gasoline does contain more energy than regular, this is not certain -- and the energy numbers are not posted on the pump.

Now that most gasolines are comingled (stored together in the same storage tank), there are certain minimum specifications that must be met by all suppliers of that grade of gasoline (usually set by a pipeline company). Volitility and octane are among the specs that must be met. Energy content is not.

You are confusing gasoline energy content with gasoline octane level. What premium gasoline does do is burn less easily than regular -- the higher octane is a measure of this resistance to burning. This reduces the possibility of premium pre-igniting before the spark fires in an engine. But the measure of octane is not a measure of energy content. And there are also some high-octane blending components that are lighter and thus contain less energy. A good example of this is ethanol, which has good octane characteristics but has less energy than even the poorest octane grade of pure gasoline.

Bottom line, you can't easily generalize about gasoline energy content.

DeusExMaxima

iTrader: (1)

Oh no, not another octane thread!!! I have put nothing but watered-down 91 Cali gas in my car, except the occasional 100 octane 76 gas. My car has ECU reflash and I noticed that there was some pinging at low end. My car seems to respond well to the splash of 100 although its ungodly expensive. When I turn off my traction control, the spark is not retarded and the car really goes. I have come to the realization that there are 3 topics that should never be discussed among family and friends: politics, religion, and fuel octane.

SilverMax_04

As I said earlier, there are many misconceptions about gasoline octane. People "know" what they know and don't want the facts. I continue to try and educate those on this site -- possibly a waste of my time, but I try.

I've said many times that if you have modded the control system in your Max, you should probably stick to premium because you have over-ridden the settings that the Nissan engineers set to allow consumption of regular at less than maximum (but generally acceptable) preformance levels for this car.

The 100 research octane racing fuel you are paying throught the nose for is only about 95 (R+M)/2 octane when compared to the 91 octane you are buying in CA gas stations. I'm told that CA set 91 as the maximum limit for commercial grade premium gasoline -- not certain exacty why they did this, but reportedly for environmental reasons.

I know you are using a phrase, but there is no (or very very little) water in the 91 octane you are buying in CA. Water and gasoline don't easily mix (unless there is something like ethanol present).

DeusExMaxima

iTrader: (1)

Ur right, there is no or very little "Water" in gasoline, but its a phrase we use here in Cali because its understood we get different formulas depending on the season and some formulas are reportedly lesser quality.

SilverMax_04

Yes, the state of CA does do things to the gasoline there -- things that I don't even know about. It's all reportedly for environmental reasons. Have never heard an explanation of why what they do really helps. Hope it is not like the ethanol farce that the US Govt. is pulling on the rest of the country -- what a crock that is.