I sure hope you did this test over a period of time didn't waste our time by posting these results after just one tank of 87 octane.

I used 93 octane in my 2003 Pathfinder for the first 5000 miles. I then switch to 87 octane fuel from there on. I saw no difference in fuel economy and certainly didn't "feel" any loss in power as some you actually try to convince yourself of.

My owner's manual says at least 91 AKI is recommended "maximum performance". As someone already stated, it doesn't say 91 AKI is required. And what do they mean my "maximum performance"? It's purposely written to be vague. The auto industry and oil companies are closely tied. Don't ever forget that. If Nissan and Infinity print "91 AKI is recommended "maximum performance", they know that the majority of people out there will use the higher octane and MORE EXPENSIVE fuel. Nissan knows that most people don't understand octane fuel ratings, compression ratios, and the science behind why a higher octane is required on some vehicles. Most people equate the higher cost of "premium fuels" with better performance. The fuel companies purposely market it this way. They also only market their premium fuels. When was the last time you saw an ad for their 87 octane fuel product? I've never seen one advertised. Only the premium fuel products get advertised BECAUSE THERE IS MORE PROFIT IN THOSE!!!!

I realize Nissan/Infiniti is not the only company that does this.

 

I've just seen, time and time again, the havoc that low octane detonation has caused on MANY heads and piston surfaces ...AND, what it cost to replace them. I've been building performance car and motorcycle engines since 68' and have more than just a little bit of a clue. It's about what higher performance/compression engines need to run properly.......not what ya can get away with. ****, with your logic I guess I should let my kids eat Mc Donalds......after all, they'll probably run just fine on it....for a while.

 

Don't confuse STATIC compression with running compression since only at the torque peak rpm does the volumeric efficiency allow close to 100% filling of the swept volume.

Most consumer knocking occurs under 3,000 rpm [light load sudden transition to higher load] due to extraordinary ignition advance to tweek the last 0.0001 mpg out of highway cruise.............tip in retard is not fast enough.

More critical is how base fungible gasoline is octane enhanced [oxygenates [MTBE or ethanol or not]] to 87 or 89 or 91 or 93, as oxygenated versions have 5% [some 9%] less BTU so it takes 5-9% more fuel to accomplish same work.

A factor often over looked that oxygenated fuels are much less efficient since they fool the O2 sensors/ecu into running richer [burn more gas per rpm].
They are usually more polluting [volume wise per mile] since you burn more per mile.

Most locations have no choice but focusing on the octane number on the pump is very error prone..........since a 91 octane version can be called 93 at a higher altitude [Atlanta at 1000 feet AMSL vs Savannah at sea level] same fuel just 3.3% difference in real running compression.

 

 

This is just plain wrong.

From Facts about MTBE (http://environment.about.com/cs/waterissues/a/MTBE.htm)
"MTBE (methyl tertiary-butyl ether) is used almost exclusively as a gasoline additive used to reduce smog (ground-level ozone) in the US. It is one of a group of chemicals commonly known as "oxygenates" because they raise the oxygen content of gasoline...Oxygen helps gasoline burn more completely, reducing harmful tailpipe emissions from motor vehicles."

You simply can't conclude that the oxygenated fuel is more polluting if that fuel is burned more completely and is therefore "reducing harmful tailpipe emissions from motor vehicles."

 

I'll bet that if you run an objective test, really drive the car the same way on the same terrain, that there will be no discernable mileage difference. This is based on normal use, ie wide open throttle is only occasionally used.

I have over 25000 miles of 87 octane use with me 2003 G35s, and the car is totally happy with the fuel. I routinely get 20 to 21 mpg in Houston use, and I am definitely not easy on the throttle. On the highway, I can see 25 mpg at 70, but I have a hard time keeping the car below 80 - 85 on the interstates. At this speed, the mileage is only about 22 mpg. Yes, I have a good radar detector that has been paid for by the savings I have accrued at the pump.

There is never any audible pinging because the engine control system is designed to use this octane. Just see section 10-3 in the manual.

Interestingly enough, this section ends with the statement that "you get the greatest fuel benefit when there is light spark knock for a short time under heavy engine load." This seems to fly in the face of the argument that increased octane is linked to improved gas mileage.

 

This'll go on forever until two identically driven G's (one on 87, the other on 91/93) have their heads pulled and compared at say 50,000 and again at 100,000 mi. Since that'll never happen, this argument will go on forever I guess. Oh well, I guess we'll all just go on do'in whatever makes us happy or what fits our budgets.

 

Do whatever makes you happy, but pick a side. Don't go with mid-grade. You either A) aren't getting full performance, or B) aren't getting the full (supposed) value of cheaper gas.

I tend to side with the "why skimp on gas with a car like this?" bunch. That being said, I've also run 87 octane for about a 6 month stretch.

My observations: Mileage difference is negligible. Power loss with 87 is unnoticeable when commuting to work, and a little annoying (but minor) when driving aggressive. When driving aggressively, mileage drops from about 20mpg to about 15mpg, and the difference between 87 and 91 becomes even less.

I don't remember who did the math in this thread the first time, but who manages to drive a G35 for two whole weeks without filling up? I certainly don't. Figure a tank a week, so >$200 per year difference for me.

Sure, gas prices are going up and that's not good.. but 87 is also more expensive than it was last month. There's still just a $0.20/gal difference between 87 and 91. If $200/year for gas is that big a deal for you, perhaps you should rethink the class of car you're driving.

Sure, the G35 is a great value in the world of luxury sport sedans, but if your car payment and insurance and other life's bills make you cringe when debating 87 v. 91, perhaps you should consider a car with a lower price tag, no "high-performance vehicle" insurance ding, and better gas mileage.

I'll be getting about 12mpg for a 1/4 tank on 91 at the autocross this weekend.