Your thinking is based on an old wive's tale.

The rating on gas is its resistance to pre-ignition, which is caused by high temperatures mixed with the compression from the cylinders. A higher octane fuel will not ignite prematurely as easily from the conditions as a lower octane fuel.

When you introduce a high voltage, high temperature spark, whatever fuel is in there will ignite. The small amout of resistance to pre-ignition will have no bearing what-so-ever on whether it will ignite or not when the spark fires.

Therefore, you will get the same mileage either way. You would probably get better mileage from the 91-93 because it is usually kept cleaner than the 87 and contains less water and other contaminants.

 

[QUOTE]If you put 93 into a hyundai elantra youre going to get worse mileage because the fuel will be unable to ignite... Just because whoever told you that worked for a gas station, doesn't mean they know how cars work

They may not have been right, but my first car was a 88 Pathfinder, V6 sport 4X4. LOL, you know the ones with the 2 doors and triangle rear quarter windows. Any way, it had 182K on it when it was handed down to me, and i swear on any thing that it ran better, and saved fuel when I used 93 or higher. The people i worked for may not be experts, YOU may not be an expert, I may not be an expert, BUT I WILL SAY that I with out a doubt got better economy out of that 88 with a higher octane fuel.

Also on a side note, using a higher octane fuel combined with a synthetic oil will give you'r engines more detergents, also helping your engine run cleaner. That means that you shouldn't have to use cleaners such as fuel injector cleaner or do an engine flush.

Ever open an engine that was only ran on high octane or race fuel? I have and if you ever did you would notice that it is almost clean as a whistle, hardly a spot of carbon on the cylinder heads. If you open an engine that was ran on low octane, the heads will be covered in carbon...Thats a fact.

Im also ultimatly still sticking to the fact, Mc2, if your REALLY driving a G, does a couple dollars a week really mean any thing to you? whether its a fact that the higher octane would give you any benifit or not, its still nice to have the peice of mind that if it did, you got it.

 

[QUOTE=G35MR2]Oh, i never said a couple of dollars a week matters to me at all. I put premium 91 (california) into my G just as the manual states.

Higher octane fuel has more detergents? I use Chevron. Chevron puts the same detergents into their 91 as they do their 87. And their 89 is created by mixing 91 and 87. It's all the same **** so to say.

No i have never opened a engine that has ran only on race fuel or high octane fuel. Have you? When was the last time you have done so? And if you have, i imagine the only engines ever ran ONLY on high octane fuel/race fuel are probably those that are rebuilt ever X number of races.

But either way, if your 88 pathfinder had 182 miles on it i could imagine the carbon build up and the amount of predetonation could easily create worse gas mileage. In that case it would make sense the higher octane improves gas mileage since less of the fuel is being wasted by pre detonation.

 

If the "small amout of resistance to pre-ignition will have no bearing what-so-ever on whether it will ignite or not when the spark fires" then please explain why it would have bearing on knock by using a lower octane?

 

Yes actually I have opend my MR-2's engine Twice. This first time on my stock 3SGTE USDM engine which i had since 22K and when i ugraded the head gasket, and there was practicly no carbon. Another time is when i got my 3rd gen JDM swap and i opened the head to port and polish it, titanium vavle springs and so forth...there was a little carbon but not much at all, obviusly it came from another driver so I am not sure what kind of fuel he put in it. Were are you trying to go with this any way?? Your really getting my confused being devils Advocate here.

 

knock is not caused by the spark, it's caused by the pressure in the chamber and the heat in the cylinder to combust the fuel/air mixture. since it detonates at the wrong time it puts a lot of stress on the internals. the spark from the plug only fires when the piston is at at the right phase in the 4 stroke cycle. If the spark ignites the mixture, then it is the correct timing for that cylinder, thus the spark does not cause pinging. the higher the octane rating, the more resistance it has to detonation while the piston is compressing the fuel/air mixture, and prevents the mixture from prematurely detonating which causes pinging.

 

oh and one more thing. I went to the turbonetics open house today like 100 other 350z / G35 owners out there, but fortunately I had a chance to talk to the 2 Nissan engineers: Mike and....I forgot the other guy's name. Anyway I specifically asked about running 87 / 91 in our engines and they said that for everyday driving around town, 87 would probably work. However, there are some problems. By running on a lower octane fuel, you are relying on the knock sensor to retard timing (which it does up to 8 degrees) to prevent knocking. However, for it to detect this, the engine must first knock....which is bad. Also, the Nissan guys said that the knock sensor doesn't work as well in the high rpm ranges since it's hard for it to determine between the knocking and the engine noise. Thus if you use 87 and drive the car hard, you're putting unnecessary risk with low octane. He said that even if you ran it on 87 and didn't get knocking, you're running the engine close to the detonation limit and could potentially cause damage still. Basically, their point was, why spend all the money on a good car and be cheap on the gas.

Oh and as a last note, I also asked them about break-in and using synthetic oil. They said 1000 miles is sufficient time to run on regular motor oil before switching to synthetic. You don't need to wait to 5000 or anything. And they also said when you go to the track to do your oil change BEFORE going to the track, not AFTER. Change oil, then go to the track, then drive on the street for a while, then change oil before the next track day. Don't wait until after the track to change the oil. Street driving is so much easier on the car and it can handle not quite 100% oil, but at the track, you want your oil at it's tip top shape to protect the engine.

Whew, I think that's about it. I'm really glad some Nissan Engineers came out to support this event.

 

why buy an expensive car then be cheap about gas? if you spend 30k plus on a nice car, then pay the extra 10 - 20 cents on the gas...

ADDED: whats "knock"?

 

i live in california and we ONLY get 87, 89, and 91 octane (due to higher emission standards). so, for those who live in states that offer 93 octane or higher, you can always go down to your "middle" octane of 91 and it would still be considered "premium" gasoline. actually, i keep hearing from ppl on this forum that they get lower mpg on 93 octane gasoline or higher. i don't know if it's true or not, but it's keeps showing up on this forum.

for me, like most g-drivers, i wouldn't dare put in anything lower than 91. i also would feel too guilty. it'll be like i'm abusing my baby!!!!

 

just to see the effect of octane grade on gas mileage and knocking etc, I did two fill-ups of 89. There was no visible change on gas mileage and no noticeable knocking. However, my last fill-up i reverted back to 93, and this time my gas mileage has seemed to drop a lil bit !!!!!!;

 

Your 3SGTE i am assuming ran on 93 octane at best. This is hardly considered high-octane fuel, highER octane fuel maybe, but certainly not high octane fuel. And the 3SGTE is obviously built for premium fuel since it's turbocharged. I don't know what else you would put in there.

I'm not really trying to go anywhere with this. I just don't want everybody running around thinking that higher-octane always means better because it's not the case.

 

If you were explaing this to me, thanks, i know what knock is. I was just making a point to the other poster that if octane rating has NO effect on the ability of spark to ignite it at the piston then why would it matter when it's in the combustion chamber.

 

So when you consider the additional costs for fuel additatives to keep your engine clean and the lower gas milege from running 87, how much money do you really save?


I experienced the exact opposite after Katrina.

Usually the difference between 87 and 93 is approximately 20 cents. If I fill up on days when some stations have a 5 cents off for premium the difference is 15 cents.

Right after Katrina the difference between 87 and 93 soared at some places to as much as 45 cents.

The pricing right after Katrina was an anomaly, and pricing fluctuated wildly from station to station in the same community. As a matter of fact there are significant pricing differances in the same area even during normal times. I live in Monkton, MD and work in Hunt Valley, MD. On 9/23 93 octaine gas sold for $3.14 in Hunt Valley and $3.01 at a Shell station a few miles north of Monkton which is in northern MD near the PA line. These two stations are about 14 miles apart and the cheaper gas is located in the country, go figure.

Since almost everyone seems to be using 87, it seems to me that the demand will drive up its price. While I was getting gas last Friday I saw a guy pull up next to me in an '05 Jaguar XJR. I know this car well since I test drove it twice before deciding on the G. The XJR has 390 HP and decently equipped stickers in the $80s. So I dalleyed for a few seconds just to see what octaine this guy was using, and as I'm sure you've guessed by now it was good ole 87. Since the G35 is a moderately priced car I can see where some owners might like to save a buck or two on a fillup, but when a guy who owns a $80K car does the same thing, I just have to scratch my head and think WTF is the guy thinking.

 

+1 (20 gal tank actually)

Higher octane the faster the fuel burns up so... lower octane would be pretty normal?

 

The Nissan engineers also said that the engine will run better on 93 if you can get your hands on it (ie. outside of California).

By the way I remember Mike's last name, it was Kojima. He's a chief engineer with Nissan and a writer for Sport Compact Car. If you don't want to believe what he reccomends (who is more of an authority than anyone here), then good luck with your engine.