Is Premium gas really needed?

[old geezer]

Hi all,

I just purchased a 1997 Nissan Maxima SE and have read lots of talk about using premium gas. So, is premium gas really needed or is it just a preference. What kinds of symptons should I look out for if I use the regular 87 Unleaded gas? I'v'e had the car for 1 week and am getting ready to gas her up, so I'm trying to get a feel as to what gas I should use.

Thanks in advance

Old Geezer

[THT]

Yes, it is necessary. Engines like the VQ30DE that powers the Maxima are high compression engines; the Air/Fuel mixture is compressed to 11 atmospheres in the firing chamber before it's detonated by the spark plug, IIRC.

If you'll recall back to high school chemistry, when you compress a gas, it becomes more volatile and combusts at lower temperatures. This is important because the more your compress the A/F mixture in the firing chamber, the easier it is for the radiant heat from the engine block to detonate the mixture. This is problematic because it drives the piston down before it (and the crankshaft) are ready. This is knock.

Premium gas is of a higher octane than regular gas. Contrary to popular belief, higher octane does not always result in better performance (from a horsepower standpoint). Octane retards ignition so higher octane fuels require more heat to detonate, thereby lowering the chances of predetonation. That's why people who are running nitrous oxide or forced induction run 93+ octane fuel.

The onboard computer can do nothing to overcome the lack of octane besides retard the timing advance. On the Maxima, if the knock sensor trips, the ECU automatically retards the timing and you lose 20% of total power throughout the entire RPM range. I'd rather pay the extra dime per gallon and get the full potential of the car, even if I'm always cruising at 2,000rpms.

If the knock sensor trips, your car will be sluggish, especially when you floor it. Run the premium, it's worth it in the long run.

~THT

[TeHsU]

thanx dude, i was putting in 87, and my transmission was making noises, when i put it in drive, you could hear it change, i put 93 in, and no more noises

[Swonder67]

Originally Posted by THT

If you'll recall back to high school chemistry,
~THT

I don't recall back to highschool anything. lol

[i3o2Matt]

does that apply for the older maximas?? cuz i've been runnin 87 octane n im juss curious

[THT]

The principles apply however, older engines such as the VG have different compression levels. If the ratio is lower, you can run lower octane fuel.

~THT

[old geezer]

Thanks THT!

I went ahead and put in the new Shell V-Power gasoline. I figured it will be approx $3 more to fill up my tank.

[THT]

And believe me, it'll be worth it. Good choice!

~THT

[ogparjay]

i only put plus cause i can't afford getting supreme all the time.

[gregory1041]

What would happen if I put 100 octane fuel in my 97 Max? I haven't done it, but was curious as to what it would do. The engine is stock.

[95maxsewv]

I have been putting that V power in from shell.. Car seems to like it... I think I have used both 94 octane and 93 from shell.. is that possible?

[THT]

100 octane would result in less chance of predetonation, nothing else.

~THT

[vinceleto]

THT

It sounds like you know what your talking about, that was a great eplination of regular to premium. Is there a actual knock or ping noise that you would hear? I've used regular some times just to see if it would shut of my SEL. For some reason it has, "the code that autozone pulled was something about the CAT Po420 I think" Anyway when I use regular I notice that if I am light on the gas and approach a hill etc. the engine hesitates with a ping type of noise. But if I'm on the gas I never have a problem the car runs fine Regular or Premium. My only concern is whether this can cause future problems like a bad oxygen sensor or something like that. I would appreciate your input.

[THT]

Yep, when there's knock, you'll here a metallic "ping" sound. Our knock sensors have a crystal piezo element (I think that's what it's called...) that is tuned to respond to that specific sound frequency so the ECU knows when knock has occurred. It's not very loud so if you have your radio playing, you may not hear it.

As for causing other problems, switching gas grades can gum up your cat IF you're switching with an ethanol blend. And usually, a bad O2 sensor will cause the knock sensor code when in reality, your car's not knocking.

~THT

Originally Posted by Swonder67

I don't recall back to highschool anything. lol

lol and i never took chemistry...lol