Fuel Recommendation?

[GTS Jeff]

This is carried over from the Sentra thread, but it's way OT, so here's another thread.

Apparently, the Sentra Spec V needs premium. You know, if that's true, I'm wondering what Nissan is doing..

There's an Altima in my driveway right now, with the same QR25 engine as in the Spec V, tuned to produce the same output as the QR25DE in the Spec V, and the manual clearly says that regular grade fuel with 87 AKI is recommended.

Maybe Nissan is just using octane requirements as a form of marketing???? The Spec V could be made to seen as a more "high performance" car since it "needs" premium, while the Altima uses regular grade to show that Nissan has "economy" in mind.

What gives???

[G]

The engine maybe the same but the compression maybe tuned differently. High complression engines need high octane fuel. I am just guessing so don't take my word for it.

[Ferio_vti]

Originally posted by GSpot
The engine maybe the same but the compression maybe tuned differently. High complression engines need high octane fuel. I am just guessing so don't take my word for it.

That's probably the answer. Go to Nissan's website and check the numbers.

[HRD2PLZ]

Same type of thing with our MDX. It has the same engine as the 02 Honda Odyssey and the 03 Pilot. Neither of the Honda's require premium fuel, but for some reason the MDX does

Same with my old Probe. The manual said to only use premium fuel (I always ran regular ) A Mazda 626 with the same engine only needed to run regular.

[GTS Jeff]

The compression ratios are the same. 9.5:1 in both cases.

As for the MDX/Odyssey engine, it "does" run better with premium, but it just uses anti-knock sensors to retard ignition timing when lower grade fuel is uses. Maybe the same is true about the Altima/Spec V engine. I'm gonna try some premium in the Altima next time..

[szw]

Well I've read countless threads about the same thing, except from people who actually own the car.

Some use 91 just because the manual says so, but you are right, it doesn't make sense. Many have used 87 and 89 octane as well, with no ill-effects as to date.

Going off-topic (slightly only...hehe)...is it true that at higher elevantion, it is safer (NOTE: not always safe!) to run a little lower octane? For example lets take a different engine that we KNOW requires 91 octane. Say you only have 89 available, is it safer to use it a sea-level, at our altitude, or does it matter?

[speedracer]

If the manual states that XX Octane is recommended then it is unlikley more octane will help. It will only lighten your wallet.
I would check into the ECU on how the fuel management is setup.

Don't forget the higher the octane the less "clean" it will burn.

As for using something lower than what the factory wants it can be done since for the most part the ECU will take that into account - BUT - all ECU are slow learners which is bad.
Also, don't epect the same power output . So the lesson is to not be cheap and use what the factory wants.

[2000impreza]

the SE-R probably has different timing and fuel maps. higher advance timing = higher octane needed.

[GTS Jeff]

To my knowledge, hte engines in hte Spec V and the Altima are the exact same - same ECU, same compression ratio, same ignition timing, same everything.

Anyway, I'm going to find out if there's a difference in power the next time I gas up my Altima.

Sean, I've also heard that lower octane can be used at higher elevations...but I'm not sure why.

[James]

I was trying to find out something similiar to this in another thread before. Because my car has only ever had Premium gas('86 MR2), and I Didnt think it was really neccisary, which Rage2 agreed with. It only Factory reccomends 87 octane, Plus it was originally from B.C., so up until last year, it would have had even higher octane(94 i think, they have ), But Could it somehow harm the Engine to start using 87 after 16 years of atleast 91? anybody have any thoughts?

[speedracer]

Originally posted by James
But Could it somehow harm the Engine to start using 87 after 16 years of atleast 91? anybody have any thoughts?

Nope. it shouldn't harm the engine in anyway. Plus think of the savings for new toys for the car.

Going down from what fatory recommends is where things get mucky. Some ECU will account for the change and some don't.

[5.9 R/T]

I'm pretty sure all engines in production cars today can compensate for low octane fuel. With knock sensors the ecu will automatically cut timing (retard) on your motor. This ensures that knocking, a.k.a detonation, (the premature and uneven ignition of fuel) does not occur. Early spark means no detonation, see? So its like a failsafe to prevent damage to your engine, therefore running lower octanes than recommend doesn't do anything but cut a few hp. Also every ECU is different and will perform this task in a different way. I am almost 100% postive that every car has this for a few reasons. You can't always get premium, 'premium' is not always the same octane rating from place to place, there is always the possibility of a 'bad' tank of gas, and extreme ambient conditions can all preclude to knock, therefore making it mandatory that a car carries a knock sensor and be able to adjust accordingly.