Hi, Sorry if this topic has been used to death before... but I would like to know if X drivers see any significant difference in power/economy when using low octane fuel vs high. I think the book says 87 for a 2004 SE... I have always believed in high octane - I ride a bike which struggles on low octane.

Can any type of tuning/chip be done to maximise the performance vs octane of fuel used? - one for the tech heads~!

Mine is a new (to me) car and I'm on my 4th tank of gas so can't make any empirical measurement yet.

Cheers
Steve

Unless your engine is knocking you're throwing money down the toilet with higher octane gas.

My dad has a Corvette and that doesn't even get premium fuel every tank. He says every fourth or fifth fill-up and he's never noticed a difference.

You will never notice a difference unless your engine was designed/tuned for a higher octane gas due to higher compression of the engine.

Xterra engine is not like that and will not benefit from higher octane fuel what so ever.

yes. higher octane is made exactly the same as low octane, and there is no difference between the two. its made to get the extra twenty cents out of you . the oil companies know how dumb we are and sell it to us. thats why race cars use 87 octane, duh.

(the above paragraph is sarcasm)

you people are baffling me with your stupidness.

Well thanks for following that up with an explanation of what the real difference is then, Einstein.

For those of you who don't know, think of octane simply as a self combustion inhibiter that's added to fuel to make it harder to burn. Why it's used and what it does is to help to prevent highly compressed fuel from self igniting, before the spark plug has had a chance to explode the fuel in the cylender, allowing engines to turn out more power per liter. For vehicles not designed to use high octane fuel there is little to no difference in performance as the engine itself never puts the fuel under enough pressure to self ignite the fuel. The spark plug ignites it under lower compression and if anything, some of that fuel may not even fully burn - a reduction in performance not to mention an increase in expense.

On the other hand engines designed to run on high octane fuel loose performance and chance shortening engine life when using low octane fuel. This is because the engine compresses the fuel in order to fit more fuel in a tighter space before ignition to get more bang out of the firing. Using low octane fuel in an engine like this will cause self combustion in the cylinder during compression before the spark plug has had a chance to fire - causing a knock in the engine. In this case, since the piston hadn't come full down before ignition, the cylinder must still compress full to let the valves release and renew the fuel mixture - this directly affects power as you end up wasting a fraction of the stroke for every misfire. This also damages the engine over time.

Most modern engines can compensate to some degree using knock sensors which detect the misfiring, and retard or advance the timing of the ignition to prevent this from happening. This is only to keep the engine from knocking though and does not enhance performance if using the wrong fuel. The benefit of designing engines to use high octane fuel is that you can get more performance per liter than a lower octane version of the same engine. The trade off here is expense, both the fuel and the engine components themselves are more expensive as they both must work under higher stress.

So in short, use the fuel your vehicle asks for. It was engineered that way.

edit: spelling

Thank you all for your replies, they are much appreciated...

The USA must make different fuel to Australia as I can assure you there is a significant power/economy increase when using 98 octane in my Triumph Trophy touring bike, our (previous)Mitsubishi hatchback and my (previous)Range Rover - but that was there, this is here... I don't even think they sell 98 here - in St Louis at least.

My question was about anecdotal and empirical evidence from other Xterra drivers...

I know all about carburettor tuning, but that doesn't mean much in a EFI vehicle, I also know enough about the science of engines to know fuel/air mix and detonation time is all important.

BTW race cars and bikes I know of run on av-gas (Airplane Fuel) or race mix (93 to 124 octane)... don't know what it is called here. I used to buy mine from Elf.

Probably rambling now... still looking for advice on the Xterra and fuel.

Cheers
Steve

i run aircraft fuel in my street car. 100 LL plus torco additive to bring it up to about 108. also methanol injection.

im at about 28psi though.

round here we use jet fuel in tractors and diesel trucks. when i worked at the airport, farmers would come in and buy it by the barrel.

Keep in mind that the 98 octane you mentioned is in Australia, it is measured in Research Octane Number(RON) and in the US it's measured as the Anti-Knock Index(AKI). The 98(RON) would be about 91-93(AKI) by US measurement standards (remember we don't like to follow the world measurement standards ), so if you want the same octane as Australia just use the highest octane you find at the pump.

I second that the best octane rating for the X is "Regular".

The octane rating is not an additive, its an equivalent...

All it means in modern fuel is pretty much how quickly it will burn...higher octane rating means a slower burn.

Knock sensors protect you from too low an octane, but do not add performance if you use too high an octane.

In fact, with an X, if you use a higher octane gas, you will blow unburned hydrocarbons out the exhaust.

If the engine is old and out of tune, well sure, spending more on gas every fill up can compensate for a mechanical problem.

The bikes that were mentioned, etc...are typically hand tuned...meaning you CAN change the timing to take advantage of the slower burning gas...and with a higher compression engine, etc...you can improve the performance with higher octane.

For an X, you CAN improve the performance with higher octane IF you re-program it to the new timing curves, etc.

You may blow something else out, but hey...you can do it faster.



So - the right octane, not higher octane, is the answer...

For example, lets say you are planning a trip up into the mountains in Colorado, and you want to have some extra power to get you up those steep inclines in the 14-er's, etc.

If you put in some "Super", you will have less power than if you put in "Regular", AND - If your normal regular was 87 octane, you'd get BETTER performance with LOWER than 87 up in the mountains.

Think about that.

is that why you can buy 85 octane in some of the mountain states? cool...

Yup!



"Regular" is lower octane for stations at altitude...just for that reason.

Here's a little more anecdotal information.

My Triumph Trophy 900 (1996 model) does get better fuel economy when using 93 octane vs. 87. I get approx. 38 mpg w/ 87, and closer to 44 mpg w/ 931, when all things are equal (path driven, speeds, etc.)

My 2000 Triumph Sprint RS 955i, however, gets the same 42-48 mpg regardless of which octane I use, but I typically fill up w/ higher octane because of the additional cleaning agents found in the premium fuel at the gas station I go to. My mileage on the Sprint varies greatly depending on speeds; if I stay in the double digits, I get closer to 48 mpg. If I'm cruising in the triple digits, I get around 42 mpg. Worse mileage to date was 41 mpg for a whole tank (I get 180+ miles per tank), but there were multiple jaunts to the 130mph range, which kills your mileage every time... (To the speed weenies, these speeds are usually only found on track days, and not on a regular highway)

My truck (2002 Nissan Frontier) gets the same mileage no matter what grade of fuel I put into it. I get a consistant 14 to 18 mpg, depending on city vs. highway, regardless of the fuel used. I use 87 octane in the truck, because 1) it's a bigger gas tank, and 2) even if 93 got me 10% better mileage, I wouldn't notice it... 10% of 14 is only 1.4 mpg; I'd never recoup the cost for a whole tank.

I honestly don't know why my Trophy gets better mileage w/ premium. But it doesn't make a difference in my other vehicles.

Perhaps timing problems on the Trophy?

I used to use more premium gas in my previous cars because of cleaning agents, etc... but even then I did not notice any difference in fuel economy - though I could swear I get better power occasionally - perhaps just wishful thinking.

Now with gas being so expensive I am running 87 in the X. I tried premium fuels for a few tanks and I would say it actually made it perform worse.

Edited to add: HowStuffWorks

All internet 'experts' seem to agree that to get any benefit your engine must use higher compression.

Wow.

I don't know what brand of fuel you use, but the major companies use the same cleaning packages in all the grades of fuel, and the octane # is all that changes.

In the old days (Pre/70's) we used to have better detergent packages in Premium, nowadays, its pretty much the same.

The reason is mostly that additives such as detegency are required across the board, and as the oil companies know that they'll be hit with a class action suit if they only have "the good stuff" in the higher octane blends, KNOWING that the higher octane is a waste for most engines (More carbon, less performance, etc...)...they HAVE to use the same cleaning power in ALL grades...its WHY they changed it all way back...to protect themselves from suit, etc.

In other words, they'd have to provide Regular and Mid Grade with extra cleanig power versions as well...a lot of pumps on that island.

It is of course legal to ADVERTISE the detergents in their Premium, as long as they do not imply that the Premium cleans better than their Regular.

Just to clarify for anyone out there -

Supercharged versions of the Xterra or Frontier require High test - minimum of 91 - because of the forced induction.

Regardless, do your homework, but you will find that the recommendation is there for a reason.

Interesting...
Here Chevron stations at least advertise regular with Techron, mid with more techron and high with 'even more' techron.

Now I don't know what techron actually is - but supposedly some cleaning agent.

They even show a picture of a little flask (of techron) next to reg, two flasks by mid and 3 flasks next to high octane - suggesting there is a lot more of it in the more premium fuels.

Other gas stations do very similar things here.

I wonder if the rules on this are different in Canada - which may suggest that in Canada it may be worth going to Mid-Grade fuel?

Hey TJ...

I fill up at a regional chain called, "Thornton's".

Here's the skinny on their premium grade of gasoline:

Granted, it may be false advertising, but I doubt it. Our State Attorney General pursues that pretty effectively, and I doubt a large chain such as this would risk it.

Like I said. I run regular in my Nissan. I run premium in my motorcycles. Motorcycle engines are a whole different beast vs. a car/truck engine. Try squeezing 100+ hp out of 1 liter in a car/truck engine, and you're pushing the limits. However on a motorcycle, that's pretty much the base line before I even start fooling with things.

Do you know why they even sell 3 octane levels? Marketing.

Studies show that when given 2 choices, people will generally choose the least expensive. When given 3 choices, many will choose the middle option.

That's why you'll never find an owner's manual that recommends the middle octane, which is usually 89. 87 works fine unless your engine requires premium. So, in the same way you're wasting money buying premium for a non-SC Xterra, you're throwing it away too if you're buying the middle octane level.

I guess one reason that high grade fuels come with more additives is that engines not made for it don't burn it as well, and they require the additive to clean out the extra carbon produced

whereas if you run the proper octane you don't need the extra additives because the fuel burns as clean as it can.

didn't know that, but it makes sense. I'll have to look that up sometime and maybe use for a economics or statistics class in the future.

Another thing I was just thinking about, on the topic of advertising anyway. The naming scheme for the different grades of gas. Why is Premium called Premium, and not just 93 octane? Well, obviously because the gas companies like to create an elevated sense of quality or potency out of the increase in octane, like it's better than the other two grades. You're paying more for it after all, if you don't understand the differences between the grades, then of course you're going to assume that more expensive = better. So the naming goes; "Super Unleaded" which means it's got a superior amount of less lead? I guess then Premium is more 'concentrated' or 'potent' than plain ol regular (note: lower case on regular)? If anything, premium should be called "Least Combustible" - that would be more accurate.

Ultimately, regardless of what the manual says, what engineers design for, or what the advertisers get paid for, if the guy at the pump is comfortable spending the extra money (or in your SC guys's case, feel confident NOT spending the extra money) for Premium fuel, more power to him or her.

But always check your owner's manual. I had a 2000 Intrepid and the manual specifically said NOT to use premium.

Well, if one has three times the amount required, is it better?



How many times the required amount does regular have?



Etc.

If you want it just for cleaning, why create unburned hydrocarbons to deposit in the system by using gas you can't burn, when you can just dump a bottle of fuel system cleaner in once in a while?

Arounf here, the price premium for Premium over regular is around $0.25-0.35/gal, so a 15 gal fill-up costs about $3.75-5.25 more for the premium.

A bottle of fuel cleaner, such as Techron, (which btw comes in several dilutions, so three times the amount of something that's more diluted can be deceptive anyway...) is in the same price range.

And yes - Canada is a different place when it comes to litigation.

Hmmm...just to through a wrench at you...the '05 X we were with this past weekend was running on over 114 octane race fuel...

Why?