Hello all,

I have been using premium gas on my car since I bought it. Mostly just because what you guys advise on the forum. However I saw the user manual today and it states as follows;

Sedan models
Use unleaded regular gasoline with an octane
rating of at least 87 AKI (Anti-Knock Index)
number (Research octane number 91).

Coupe models
Use unleaded premium gasoline with an octane
rating of at least 91 AKI (Anti-Knock
Index) number (Research octane number 96).

Do we have a different engine than the same year Coupe's ?
So is it completely safe to use 87 ?

 

I have an '06 Sedan, when I put Regular , California blend, it really makes the run car like crap. Slowed acceleration, and sometimes its difficult to start. Mid grade OK, Premium 91 makes it run well. I think the rest of the country premium is rated at 93 ? Not sure.

 

Modern cars have knock sensors and retard the timing when lower octane gas causes knocking. You can use 87 and probably never damage your engine, but I would run back to back tanks with premium, then 87 and compare mpg. Most likely the savings of regular will be offset by lower mpg.

FYI the higher octane number means it is more resistant to detonation.

 

^ that man speaks the truth!

Also engines SHOULD be the same but the tuning on the coupes were a little more aggressive tuning hence why on paper they normally show a couple of HP higher.

 

Well stated. And in being more resistant to detonation, it allows the ECU to advance the timing and take advantage of higher compression, hence the potential for slightly better performance. However, if you check some of the heated discussions on the forum, you will see that many say the difference is not noticeable.

I believe they changed in 05 or 06 and recommended premium for the newer models moving forward.

 

So depending on the tune, the car should more or less perform the same? Hmmmm. I have the Rev-Up 6 speed manual, and to me 87 makes it run awkward, but functional.

 

Not true. If the motor senses detonaton it will switch timing maps, probably why you say "awkward, but functional". When we dyno'd my car it was switiching to the high detonation map, getting it to stay in the standard timing map was worth 20 horsepower.

 

There were a few threads not too long ago where other members proved my beliefs wrong and taught me a lot.
That led me to do a pile of additional research, etc, and I actually did up a chart after citing a bunch of different sources, including HP ratings, etc.

Here it is, follow this and you will be fine:

2003-2004 6MT and 5AT SEDANS: 87, with 91 recommended for better performance
2005-2006 6MT SEDANS: 91
2005-2006 5AT SEDANS: 87 with 91 recommended for better performance
2003-2006 Coupe (all): 91

 

Also, on top of different tuning 'maps' for each model, the 6MT sedan got different camshafts vs. the Automatic.

Nissan did a bunch of things differently across the models and years, but follow the above chart and all is good!

 

In my '05 6MT REV it states that if there is no 91 available, fuel a minimum of 87 to drive to the nearest 91 available, and do not make hard accelerations. I was almost scared reading that !!

 

Really? I have never heard that. I knew the rev-up had different cams but I thought 03-04 6MT was the same as 5AT. Not that there would be any reason to find a set of these cams when S1's and S2's can be run with stock springs, but nice to know.

 

It looks like only the rev up got different cams, correct.

 

That is true, but I would still put octane 91 to be better off.

 

thanks guys.

I use 93 almost all the time. However sometimes it is really too expensive. From time to time, the difference is as high as 50 cents per gallon which makes around $10 of difference per tank.

Is there any absolute numbers in the increase of mpg when you use 93 instead of 87?

This is just out of curiosity, I will probably use 93 all the time.

 

Higher Octane allows for more advanced timing which allows the combustion cycle to occur closer to top dead center (better power).

Low octane fuel will cause detonation with the more advanced timing, so the ECU will back the timing off (retard the timing) until it no longer senses detonation. Like others mentioned, it will run, but not run as optimal as it would with the higher octane fuel. But for some, that is good enough.

Back in the 70s-80s when we didn't have ECUs, you had to figure this balance out on your own.

i believe all the 2nd and 3rd generation Gs utilize a higher compression ratio which requires premium fuel (at some point, the ECU will not back the timing off any further).