Taking advantage of higher octane gas

Messages
491
Location
Arlington, TX
Im trying to see if using higher octane gas for my new 06 titan will result in better performance or mpg. But first, i would like to ask someone here several questions that got me pondering about this issue... i believe i have a knock sensor and a distributeless ignition timing system. I have only run regular 87 unleaded ever since the day i bought it. Manual calls for 87 but i intend to see if i can notice the difference in performance and in mpg. So... that being said.. 1)How would you approach this (should i run a couple of tanks of plus before using premium)? 2)Would there be any problem with switching from premium or plus back to regular on occasional basis? (sorry if this sounds very newbie but im still learning). Thanks for any inputs
 
Messages
3,558
Location
SE Pa
Other than the possible benefits of higher detergency found in some premium grades, it would likely be a waste of money to run higher octane fuels in an engine designed for regular. The better test is to experiment with various brands of regular to see if you notice any mileage difference. Some claim this with Shell fuels.
 
Messages
2,338
Location
Charlotte Metro area
Highroller, several things you should know. "Octane" is, in reality, "anti-knock" index. The higher the anti-knock index, the SLOWER the fuel burns, the harder it is to ignite. Vehicles that have higher compression ratios create more heat in the combustion chamber each compression stroke, and the fuel needs to be more resistant to ignition so it won't ignite prematurely and cause knock. Higher anti-knock fuel often has lower total BTU's because of the anti-knock additives. These additives can put down deposits in the combustion chamber, as the anti-knock compounds sometimes don't burn as cleanly as the gas. These deposits can become hot-spots themselves...actually glowing red-hot, and can be sites of premature combustion ignition, requiring higher anti-knock fuels! Stick with what your manual recommends. If you are looking for the best mpg, lower octane will generally be better, unless your ECU and engine design is set up to take advantage of an advanced ignition timing. Even if it is set up so, you might not get better mpg, even though you MIGHT get better power under load. I certainly wouldn't recommend going from 87 to 93 on a vehicle spec'd for 87. It's a waste. If you are looking for better cleaning, better mpg, you might consider Fuel Power. I use it for cleaning, and run the cheapest gas in town. My mpg increased noticeably in three vehicles....could be the FP? Don't know for sure, but my wife's city mileage in an automatic is 5.5 mpg better than EPA estimates...and she didn't know I had done anything different to her fuel. My manual transmission car gets almost the hwy EPA number, and my motorcycle gets 8-10 more mpg than it used to...on regular gas, even though it is spec'd for premium due to pinging tendencies. No pinging. Excellent combustion chamber cleanliness. I'm happy with the results, to say the least.
 
Messages
1,053
Location
Indiana (IN)
Your car may be able to adjust to the higher octane and produce more power. Dinan has a white paper on running BMWs on a dyno. They showed a 3% improvement in max power just from switching from 91 octane to 93. You might see 5-10% higher max power output from switching from 87 to 93, but at most normal speeds the gain would be little. It would not offset the higher cost of the premium fuel in higher mileage. You have an ODBII vehicle so you could get a connector and PC software to monitor the actual ignition timing and see if it increases with the higher octane fuel. Search on the internet for ODB II.
 
Messages
882
Location
North Carolina
Highroller your knock sensor equipped engines computer "knows" when the engine is on the edge of a sparknock condition. The knock sensor is an electro-accoustical device tuned to "listen" for the noises sparknock creates. Sparknock is uncontroled combustion of the fuel/air mixture. Rather than orderly burning sparknock creates more of an explosive effect with sharp pressure spikes in the combustion chamber. Tendancy for sparknock is aggrivated by increased compression ratio,deposits,spark advance, engine temterature, air temperature,reduced octaine,lean fuel/air ratio,and engine loadinng.In no particular order and I probably left some out. Out of these causes the engines computer has control of timing advance, air/fuel ratio, to a degree engine temp, and if so equipped,EGR. You have control over loading and octaine. These controls combine to create a great deal of flexability in engine operation not generally avaiable until '95 or '96 with the universal mandate of OBDII engine controls. Your engine "should" be able to take advantage of the increased knock resistance of premium by retarding the spark advance less often resulting in more efficent operation. As for octaine enhancers in street gas: most blends in my area utilize aromatic hydrocarbons or other octaine enhancing petrolium constituents to increase octaine. These will burn cleanly and do have some detergent effect. Ethanol will also increase octaine. One minor problem with ethanol is it has considerably less energy content VS: gasoline. So with ethanol blended premium you may pay more for the same or less fuel mileage VS: non ethanol regular. Deposits? MMT which was phased out several years ago was an excellent octaine booster which unfortunately left lots of deposits comes to mind. Modern premium? Unless the owners manual specificaly forbids premium... no problem to give it a try. My personal best gain with premium has been about 2 MPG with some increase in engine response. Maybe the increase in "peppiness" is placebo but I believe it is real. Don't worry about mixing grades or transitioning with midgrade. Most midgrades are a mix of regular and premium any how. Good luck with your new truck,enjoy.... Rickey.
 
Messages
441
Location
Toronto, Canada
This general issue seems to be coming up more. Is this one of engines that does not "require" 91AKI except to obtain best performance. Toyota, Nissan and I think Honda have been increasingly defining engines in this way. eg run 87 AKI by default but if you run 91AKI the computer will adjust timing to take advantage. Worst case scenario with that engine using FP60 and 87 is normal performance plus the advantages of FP60.
 
Messages
2,338
Location
Charlotte Metro area
Rickey wrote: Your engine "should" be able to take advantage of the increased knock resistance of premium by retarding the spark advance less often..... Had to read it twice, but, that part is accurate! However, depending upon how the anti-knock index is raised, it wouild be extremely difficult for an OBDII feedback control to be more efficient when using a fuel that is anti-knock index raised with substances that have less energy per unit volume than 87. Ethanol was a fine example. It depends! Really like what peterr wrote: Worst case scenario with that engine using FP60 and 87 is normal performance plus the advantages of FP60.
 

vad

Messages
1,856
Location
So Cal
quote:
Originally posted by Highroller: Manual calls for 87 but i intend to see if i can notice the difference in performance and in mpg.
Chances are that you'll see no difference or slight decrease in mpg under the same driving conditions. Let us know please.
 

Highroller

Thread starter
Messages
491
Location
Arlington, TX
Thanks to all those who have given me great inputs so far, appreciate the advices really much. Im learning something new everyday here, it's awesome. Well, from what i have heard on here and elsewhere, i believe this engine can take advantage of using higher octane gasoline. But, before i get started on this and i do intend to post what my mpg/performance during my trivial runs, i would like to know if there are any effects of running a couple of tanks of premium and then switching back to regular. For example, would i see an increase in fuel consumption or if the car will run sluggishly after switching back to regular, etc? My plan is to run 4 tanks of 89 and then 4 tanks of 93 using shell, and then 4 tanks of 89 and 4 tanks of 93 using chevron gas station for my little mini experiment.
 
Messages
2,387
Location
Chicago area
Getting a chip or reflashing your computer is the best way to get the full benefits of higher octane fuel. With stock programming that recommends 87, you probably will run better with mid grade, and really have no need for 93. You could unplug your knock sensor and test each grade of fuel, listening for knocks under various conditions. If you knock with 87, go up a grade. Then you can plug your sensor back in. I use premium fuel in my Superchipped ZX2, and leave the knock sensor out of the circuit. They are too sensitive, and pull a LOT of timing. They activate from other ambient vibrations, also. The car runs beter with good fuel and my sensor unplugged - smoother power band and more power. The sensor IS a safety device - if you take control you have to have good fuel.
 
Messages
665
Location
GA
In most cases I would say dont bother with the higher octane but I do believe that the Titan can take full advantage of premium. When is was first introduced they actually reccomended premium but quickly changed the requirment to 87 because most of the people that bought them didnt want to pay extra for fuel. The Infiniti QX56 has the same engine and driveline but is rated 10hp more and 11 ft lbs more torque. Ive heard over and over that the ecu is the same unit also. The 5.6 in the Infiniti and Titan share the same compression ratio as well.
 

Highroller

Thread starter
Messages
491
Location
Arlington, TX
- mechtech, thanks for the advice, that's really informative. Although id love to unplug and see like you said, i just intend to leave the knock sensor in place and just test the midgrade or premium with that. -Anthony, im really curious to how u find out that they recommended the premium? I will be experimenting with both grades (midgrade and the premium), but mainly for my own benefit, i would rather lean toward a particular grade if i can, to get the best performance and mpg. I forgot to mention that i do sometimes take my truck out to the track just for fun and to record my times. On occasions, someone would pass by and try to race, so id love a good win over the competitor also. Everything is stock, no modification.
 
Messages
1,151
Location
Clovis, CA
If you really want to give your truck the primo stuff give it Chevron, but just buy the regular grade. Plan on spending upwards to an extra $0.40 for the Chevron though.
 

vad

Messages
1,856
Location
So Cal
quote:
Originally posted by Anthony: Ive heard over and over that the ecu is the same unit also. The 5.6 in the Infiniti and Titan share the same compression ratio as well.
The ECU might be the same. But the software is definately not.
 
Messages
36,405
Location
ME
Give it a shot, even the naysayers should admit you won't harm anything in the short run. Midgrade gas is usually the worst value for dollar. Premium around here is only 7% more expensive at current prices. OBD-II has nothing to do with knock retard programming, knock sensors have been in turbo cars since the 1980's. It's simply coincidence that feedback knock control* has gotten more use in the 90s and beyond. *I liken feedback knock control to the feedback fuel control we got in the 80's. You'll remember the late 70's junk was set up to run real lean and had no power-- so the 80s got feedback fuel control to more consistently stay stoichometric. As knock sensors got better in the 90's they figured compression could go up and started to "count on" knock retard as a basic part of the engine design. They've been pushing that envelope ever since. You should find your computer relatively quick to clamp down to a normal, semi-retarted timing map if you ever put cheap gas in. However, it may take a couple tanks of the good stuff for it to slowly test the limits and give you more timing, power, and economy. All in the name of protecting the engine from detonation.
 

Highroller

Thread starter
Messages
491
Location
Arlington, TX
Im currently running midgrade (89) as of currently. i will run about 3 more full tanks of this and record my mpg/performance and then try my hands on premium. So far, i feel a slight increase in power (feels like im pulling a heavy load or something?). I regularly follow a fairly simple routine of city/hwy driving everyday. Ill try to post my findings.
 
Messages
665
Location
GA
The infiniti and the titan software is the same. If you can find a very early titan brochure, is said premium reccomended. Im talking about brochures from december 03.
 

vad

Messages
1,856
Location
So Cal
quote:
Originally posted by Anthony: The infiniti and the titan software is the same.
Can't be. It is just impossible.
 
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