octane

[karate_kid]

I have a normal stock 240sx and I am wondering what octane gas i should use. Right now I am using the lowest 87 octane.

[nnkfws333]

you can use 87 octane but it works best with anything above 91

[karate_kid]

Do i get better mileage if i use a higher octane?

[Nismo_Freak]

No... putting higher octane fuel in a car that doesnt knock wont result in more power unless the ECU actively senses the added octane. The KA does not do this.

If you have a S14 the recommended fuel is 91 octane or higher.

[Mayhem_J30]

No... putting higher octane fuel in a car that doesnt knock wont result in more power unless the ECU actively senses the added octane. The KA does not do this.

What do you mean? I thought it probably wouldn't knock anyway, because the ECU will retard the timing enough to compensate for the octane deficiency?? So when at optimized timing and 91+ octane wouldn't the most power and MPG be increased to?

[Cyberkreig]

The ECU only retards timing when the motor knocks. He said "In a car that doesnt knock". I run 91.

[Mayhem_J30]

The ECU only retards timing when the motor knocks. He said "In a car that doesnt knock". I run 91.

but how do you know it's not knocking because of the timing adjustments? Maybe it did knock (slightly) enought for the ECU to take care of it. Only way to know is to log the knock sensor voltage.

[Cyberkreig]

Good question, and over my head. =)

[s0ldats]

but how do you know it's not knocking because of the timing adjustments? Maybe it did knock (slightly) enought for the ECU to take care of it. Only way to know is to log the knock sensor voltage.

word.

i've been using 87 until i read that 91 was recommended per the user manual. i noticed a large difference in performance. my car was less chuggy and revved more freely.

[karate_kid]

will 91 give me more mileage then 87?

[Antjaw]

I have noticed an increase in gas mileage with high octane... Also the knock that was there has gone away

[C-Kwik]

Nissan ECU's tend to overcompensate for knock when it is detected. You'll probably feel some hesitation if it does.

As far as using high octane fuels, you won't notice a difference unless you are detonating and the knock sensor is retarding timing, or unless you advance the timing. Advancing the timing would increase the peak cylinder pressure and using a higher octane will allow you to advance timing further than with regular fuel. Don't expect any miracles with this though.

[Mayhem_J30]

will 91 give me more mileage then 87?

I would say yes as this is what your motor was designed for.

[ricebike]

89-90 SOHC engines did not come w/ a knock sensor... plus my 1989 manual says i can use 87 octane.

however, my car does run better on higher octane... maybe a placebo effect or there's carbon buildup

[DAEDALUS]

Everything else being equal, higher octane gas should show a small improvement in mileage. If you wanted to cruise at 60mph on the freeway, it will take less 91-octane gas to provide that power than the amount of 87-octane gas required. I ran tests on a generator as part of a college course that proved this. However, don't use a tiny increase in mileage as sole justification to pay more per gallon. The cost is maybe 20% more, but the mileage increase would probably be a low single digit percentage.

[Mayhem_J30]

Everything else being equal, higher octane gas should show a small improvement in mileage. If you wanted to cruise at 60mph on the freeway, it will take less 91-octane gas to provide that power than the amount of 87-octane gas required. I ran tests on a generator as part of a college course that proved this. However, don't use a tiny increase in mileage as sole justification to pay more per gallon. The cost is maybe 20% more, but the mileage increase would probably be a low single digit percentage.

what about engine life? Wouldn't this be increased as well while running on 91+?

[Emperor240]

ok here's a lilttle info, the octane rating on gasoline is a burn rate mesurement. believe it or not it takes 91+ longer to burn then it does 89 this reduces the chance of detonation on a higher compression engine (thats why in the old days you had to run 94 in a 10:1 compression car, the didnt have knock sensors) so when you run the proper octane for your compression and other specs you get better performance and gas mileage and it may in some cases prolong life of certan parts but i dont know if it will for the engine as a whole

[Mayhem_J30]

Read up kidshttp://www.nissaninfiniticlub....ctanehttp://www.nissaninfiniticlub....ctanehttp://www.nissaninfiniticlub....ctane

[nlzmo400r]

i live in LOUISIANA and have an o2 2.5s and i pay roughly $1.70 a gallon for 93octane (premium obviously, and i never put less than 91 octane)

[GELLIS2586]

Ok so since my ecu from a ka24de out of a 97 doesn't retard the timing running octane booster would have a negative effect on the engine because of to low compression. Or am i just sompletely wrong here.