With the gas prices getting over $4.00/gal here in California, I did an experiment with lower octane fuel. We have 91, 89, and 87 available in So Cal.

Let me preference that my driving is mainly bumper to bumper rush hour to work with an occasional run to 70mph on the freeway if I leave early in the morning. The evening I take a canyon route because though slow moving (about 30-35 mph) it's constantly moving. A change of pace. I have a 40 mile round trip.

I ran a few tanks with 89 octane and experienced no change in performance or gas mileage. ( I get about 19.5mpg). I then ran a few tanks with 87 octane and I still experienced no change in performance and I get about 19.5mpg. No Knocking either.

Here is an article about engine compression and octane:
http://www.wisegeek.com/what-is-high-octane-fuel.htm

It states that you won't hurt a high compression engine with lower octane fuel. Though you may loose a little performance.

Now of course I would put in the high octane if I were to go on a long trip etc. but for around town I'd rather save the money.

Thanks for listening.
Bruce in L.A.

 

hey bruce, and welcome! i only use 91 octane because the one time i did try and use a mixture of 87 and 91 my car was jerking whenever i stopped at a light and i cant have that! gas is getting ridiculous in socal, i was in burbank today and had to pay 4.12 because i was on E and had to get back to torrance. but if you dont see or feel a difference in your car then go for it. i guess ill just keep getting raped with no vaseline while youll get just alittle lube, not alot just alittle

 

I ran 87 on mine..and since I don't drive that fast..I don't notice the difference...if I track it..I'll put 91

 

i ran87 once on a road trip back from home from so cal or nor cal because the gas station only had 87 (how does that happen???) i felt a slight difference in performance seeing that on I5 most people are doing 85 all the way down... doing 85 i think you might notice

 

yeah you would definitely notice at 80-85mph. hell i do that everyday, maybe thats why i felt it so much!

 

octane is a stabilizer (or a measure thereof, more specifically...right?). gas is a stabilizer in the combustion process. higher the octane = more resistence to combustion.

the vq35hr has a 10.6:1 compression ratio, but appears to use a variation of direct injection. what's that mean in english? you should stick with 91 octane and higher with 10:1 cr motors most of the time, but this one can handle lower octanes if you really insist on it. most ecu's in the last 10 years have been able to retard timing and sense knock to correct for crap gas, so you don't have much to worry about on naturally aspirated motors with <11:1 cr's.

flip side, the ecu is retarding timing so much on lower octanes that it's probably costing you a decent chunk of power. that means nothing to most of you, as the vast majority of g owners buy autos, and most of the folks on here drool over 19's and 20's, so they obviously much care about any real performance from the car. floss away. if 87 octane, and the power drop it brings, fits into your lifestyle...well great. you're not really saving that much money, but a dollar's a dollar.

 

I think I read somewhere in this forum that the ecu doesn't retard timing unless there is "knocking?" (too lazy to search).

 

What does the owner's manual say to use?

 

depends on which manual... but you cant go wrong if you follow what it says

 

the sticker on the gas door says premium. on the prior gen it said mid grade (89+).

like i said, 91 octane is about right for the CR of this motor. it's on the lower end of the spectrum when it comes to needing 91 octane+, but it's in it. the ecu will compensate for lower grades. feh, any more and i'll just be parroting my other post

 

meh, from experience, 87 doesn't work well, and gets significantly worse mileage, (in the tank per week measure, don't bother with mpg), rather than a tank lasting a week or more at 91 octane, it's a matter of or 5 days on 87, can get closer to 8 or 9 days on 94, plus there's more power and much smoother operation, so i shell out the extra .20/l or so.

it's something each driver has to ascertain his or her car's needs based on driving style and conditions, as well as how it reacts to the fuel. if you can get away with 87, go for it.

and i take offense at the statement that since i have an auto i don't care about performance. (try finding a 6mt sedan around here, not easy).

 

There are three fuel requirement statements companies use:

Regular
Premium Recommended
Premium Required

The G is Premium Recommended.

 

Every car with an ECU (PCM if you own a GM since thats what they insist on referring to it as...a Powertrain Control Module) will not retard timing unless it detects knock.

The exception to this is the Mitsubishi EVO which has been known to get so spooked with knocking if a car with a loud engine/exhaust revs nearby, it'll sense it as knock thats so severe, it'll just turn the car off.

 

Out of my 2008 G35X Manual (btw I have the sport):
"Infinity recommends the use of unleaded premium gasoline with an octane rating of at least 91 AKI (Anti Knock Index) number (Research octane number 96).
If unleaded premium gasoline is not available, you may use unleaded regular gasoline with an octane rating of at least 87 AKI number (Research octane number 91) but you may notice a decrease in performance."

sharkman

 

I don't think you have the same car as the rest of us... My manual says Infiniti, not Infinity....