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  #1  
Old 03-03-2004, 10:00 PM
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Advantages/Disadvantages of premium fuel

I was wondering what the advantages of running premium fuel are, since my parents want to get away with the cheapest gas possible. They don't care about the performance benefits, and I wanted to know if there were other advantages. I was also wondering about running synthetic oil. Thanks.

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Old 03-04-2004, 01:28 AM
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Re: Advantages/Disadvantages of premium fuel

Some may argue, but essentially if it runs fine on lower octane then you're wasting money buying premium. Higher octane <> more power, but more power = higher octane. Get it?

http://auto.howstuffworks.com/question90.htm

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Old 03-04-2004, 02:42 AM
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Re: Advantages/Disadvantages of premium fuel

nate,

I guess I'm one of those who would argue. Technically, lower octane does result in lower power. However, with the high compression ratio the VQ35DE engine has (10.5:1, if I remember correctly), anything lower than 91 octane gas will result in knock. The knock sensor will detect this and force the timing to retard until the knock goes away, but then power is lost as is fuel burn efficiency, leading to carbon buildup and, probably, shorter engine life.

IMO, it is just not worth it unless you have to put it in the tank in an emergency. Fortunately, the premium gas here in Memphis, TN is 93 octane, so the G35 is plenty happy!

Scott

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Old 03-04-2004, 05:00 AM
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Re: Advantages/Disadvantages of premium fuel

I've been running 87 in my sedan for several tanks now as sort of an experiment.

If there's a loss in power, I certainly can't tell. You'd probably have to stick it on a dyno and measure it to notice the difference.

The mileage may be dropping just a bit. It's too early to tell for sure, but it doesn't look like it's dropping enough to matter... looks like I get more miles per dollar on 87 than 91.

I used to believe in the idea that you'd lose power, and you'd lose enough fuel efficiency to make it not worth doing. I think I've been proving myself incorrect lately.

What about synthetic oil was it that you were wondering about?

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Old 03-04-2004, 10:09 AM
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Re: Advantages/Disadvantages of premium fuel

Just like ryoken, I am running 87 octane in my sedan. I notice a slight decrease in performance when I push the car. For the everyday commute, I have not had any problem with 87 octane. Actually, for the sedan, it states in the manual that 87 octane is recommended but you should use 91 or better for optimal performance. Check out your manual....

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Old 03-04-2004, 11:34 AM
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Re: Advantages/Disadvantages of premium fuel

<blockquote><font class="small">In reply to:</font><hr>

The knock sensor will detect this and force the timing to retard until the knock goes away, but then power is lost as is fuel burn efficiency

<hr></blockquote>

Hmm, interesting. I guess I'm old school back in the days before ECUs when I took a bunch of auto classes the instructers talked about octane and how it's not needed. This argument here with the adaptive ECU does make some sense. Then again, I've been largely away from the car scene for 10 years so maybe I'm confused.

However, the coupe is 'required' to have premium, but the sedan does not. Which makes me wonder again about the differences (coupe vs sedan) and why this would be. Is it just a marketing thing again in regards to the premium fuel? If the ECU will adapt then couldn't the coupe also run on regular?

I was running premium in my sedan for the first 6 months or so, but then switched. Can't say I noticed a difference and since the 'wise enigneers' at Infiniti (or maybe it was the marketing dept) said regular is OK, I figured it was OK.

Maybe I need to rethink this, but it's so hard with so much contradicting information out there.

Questions - I had heard that higher octane results in higher heat. I think what is actually meant is higher compression equals higher heat and thus the need for higher octane to prevent pre-ignition. Also, since a higher octane means it ignites slower is there a possible concern there if your compression is less? Or would this be similar to advancing your timing and thus resulting in the performance increase? Then again, maybe the ECU would come into play here and adjust for it again the opposite way making the reaction all dependant on how your ECU is tuned???


Damn ECU!!!

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Old 03-04-2004, 11:53 AM
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Re: Advantages/Disadvantages of premium fuel

nate,

Hmmm, from what I can remember, premium IS "required" in the sedan. Well, I guess it is more correct to say that it is "recommended".

Probably the difference between a "requirement" in the coupe and "recommendation" in the sedan has to do with the extra 20hp the coupe has. Still, so far as I know, the ECU in the G35 behaves as I described.

Of course, like you my days of actually digging into engines are fairly well behind me. While I hope to begin digging into the G35 sedan's engine in a couple years, when the warranty expires (will hit ~60K miles right at 4 years or so at current rate), it is still a ways off.

Personally, I think that, without too much trouble, the sedan's engine should be able to make 300-320hp at the crank, naturally aspirated, and still with all stock engine internals.

Anyway, from what I've been reading lately about engine design, the most compression you can expect to get from 91 octane engines without running into knock conditions is 11:1. And to get that, some careful work is necessary to the heads (intake and exhaust ports, and the head portion of the combustion chamber) to acheive 11:1. This is probably why Infiniti requires 91 octane gas for their engines (all of them from what I can remember). Of course, since we have 93 octane gas here, we have a bit more headroom, so 11:1 and even higher are possibilities.

Scott

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Old 03-04-2004, 12:05 PM
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Re: Advantages/Disadvantages of premium fuel

I've been hard pressed to actually feel a significant performance diff between 87 and 93, but I do find a VERY noticable diff in sound (engine, exhaust, etc.) when using lower octane. That quiet, silky smooth, highly refined sound is replaced by louder, rougher and raspier sounds. Really effects the Stillen exhaust tone. By half full, I usually can't stand it any longer and fill back up with the good stuff. The resulting "mix" of 90 or so works much better.

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Old 03-04-2004, 01:58 PM
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Re: Advantages/Disadvantages of premium fuel

Hi:
I'm new here to the forums. Great info here on the forums. Anyway, I actually email Infiniti about the Regular vs. Premiun gas for the sedan and here is their reply:

Thank you for taking the time to personally contact us about your interest in Infiniti products.
For the G35 Sedan, you may use a regular unleaded with an octane rating of at
least 87. However, for improved vehicle performance, use a premium unleaded
with an octane rating of at least 91.
We hope that this information answers your question, but if you need any
additional information or have further questions, please let us know by reply
e-mail or by calling 1-800-293-0800 and pressing "0" for a live operator.

Also, make sure to take a look at our website, www.Infiniti.com, for the most
up-to-date product information.

At Infiniti, we strive to provide the highest level of customer service.

Sincerely,
Infiniti


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Old 03-04-2004, 05:25 PM
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Re: Advantages/Disadvantages of premium fuel

UCSB94,

Well, I'll be darned! Guess that is their "recommendation". I have to admit to being surprised that they would acknowledge that using regular fuel is OK because of the reasons above and 91 octane and above is all that is listed in the statistics from the various mags, etc.

If gas prices get much higher I may have to try regular and see how much of a performance and milage hit I take. However, I still can't see how the engine wouldn't be more likely to carbon up with the lower grade fuel.

See, just goes to show that when you think you know what you are talking about someone teaches you something new...

Scott

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Old 03-04-2004, 06:20 PM
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Re: Advantages/Disadvantages of premium fuel

<blockquote><font class="small">In reply to:</font><hr>

I guess I'm one of those who would argue. Technically, lower octane does result in lower power. However, with the high compression ratio the VQ35DE engine has (10.5:1, if I remember correctly), anything lower than 91 octane gas will result in knock. The knock sensor will detect this and force the timing to retard until the knock goes away, but then power is lost as is fuel burn efficiency, leading to carbon buildup and, probably, shorter engine life.

<hr></blockquote>

What he said. Using low octane is sort of like the opposite of a cold air intake. You have to put less air into the cylinders to avoid putting too much pressure on the low octane fuel, otherwise it will detonate before the piston reaches the top, forcing the piston downward while the crank is still trying to push it up. That's where the knocking and bucking comes from. Not good for engine longevity, obviously, although the ECU should adjust the timing before it comes to that.

Since you can't get full power out of low octane fuel, particularly as the timing advances in the high rpms, low octane is only useful if you're grannying your G. In which case, why not just drive a Corolla? You can still use gas-saving driving techniques when you fuel up on premium, and at least then you'll have the juice on tap when you want to run the car the way it's meant to be run.

It kind of amuses me how some truck-buying sorts think regular unleaded is "tough" fuel for tough engines, when it's really very wussy fuel that needs to be babied and pampered.

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Old 03-04-2004, 08:46 PM
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Re: Advantages/Disadvantages of premium fuel

VQ35DE engine's compression ratio is actually 10.3:1. (Close enough. [img]/w3timages/icons/smile.gif[/img]

87 isn't tough, and it isn't wussy. It actually has more energy per volume than 93, but can't stand higher compression ratios.

The coupe is listed as "required" because of the extra power. The ECU timings are different, more aggressive, and can't cope with 87 for extended periods of time.

Here's a little math fact for ya'll, too: The difference in 87 and 91 (or 93) is usually about 20 cents/gallon. Let's say you drive 12,000 miles per year and average 17mpg. You're only saving $141 per year, and that's assuming the mileage between 87 and 91/93 is identical, which it won't be (but it won't be a huge difference). 10,000 miles and 20mpg = $100 and 15,000 miles and 14mpg = $214.

That's $8-$17 per month. If your budget is that tight, you really should consider trading the G in for a slightly used economy car. Or at least bring your lunch from home instead of eating out a couple extra times to compensate. [img]/w3timages/icons/smile.gif[/img]

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Old 03-04-2004, 10:52 PM
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Re: Advantages/Disadvantages of premium fuel

Without premium fuel the Time Travel Mode in the Navigation System sub-menu is inoperable, but...... I fear I've already said too much!!

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Old 03-04-2004, 11:01 PM
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Re: Advantages/Disadvantages of premium fuel

You mean "without plutonium fuel" right? [img]/w3timages/icons/smile.gif[/img]

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Old 03-05-2004, 05:03 PM
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Re: Advantages/Disadvantages of premium fuel

Well put Ryoken. I think it is safe to say that we G owners (on this list anyhoo) had performance as a high requirement for our purchase. Otherwise we would be on the "I" list. Let's not let those Dinosaurs down. We gotta use that fossil fuel, and make it Super. We need to let those prehistoric beasts rest knowing they didn't become extinct for nothing. T REX STILL RULES THE EARTH IN MY G's FEUL TANK!

Sorry for the outburst. It's Friday and my brain is mushier than normal.

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Old 03-05-2004, 05:03 PM
 
 
 
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