Octane

[legendbridges]

Just bought a 2007 LR3. Just wondering does anyone actually run above 90 octane like the book says? Does anyone run 87 and do those people have any problems? Thanks for the help.

[GWDRoverTX]

legendbridges,

To learn more about the different octane levels for gasoline and the detergent additives, check out the two websites below.

The Low-Down on High Octane Gasoline

Top Tier Gasoline

These give you unbiased information so you can decide for yourself.

[unseenone]

Go with the MFR recommendation. Using something else will also mess with the computer, etc. I always use the highest premium available, I want to get every possible mile out of the engine.

[GWDRoverTX]

Using different octane level will not mess up the computer. The purpose of the computer/electronics is to adjust the engine (timing, etc.) for the different octane levels.

[BD_LR4]

Can someone help clarify why folks try so hard to not use Premium fuel? There are plenty of posts on this forum which have a plethora of reasons to use it. If the purpose is primarily fanancial, the take a second look at my previous post, copied here:
"Thought I would throw in my 2 cents on this topic. Regardless of gas mileage decreases by not using premium, just perform a quick calculation on the price difference. Assume 15,000 miles per year, with an overall average of 14 MPG. That would require the purchase of just over 1,071 gallons of gas in a year. The difference between premium and plus is $0.10 per gallon. Total additional outlay by using premium fuel amounts to a whopping $107 in a year. Even if you didn't buy your vehicle new (you're still talking about $30K+ for a used LR3) is the extra $107 you are saving really going to amount to much of anything? Tires and Brakes will quickly make that $107 seem like chump change. Even if you saved $0.20 by using regular, you are talking just over $200 in annual savings. "

The above assumes same gas mileage. Many posts indicate 1 less mpg by using plus instead of premium. This will almost entirely negate any savings. Buy fewer lattes at starbucks if you want to save money.

[Disco Mike]

How about because the manufactures says so, if you don't, it is a proven fact, you will have less power, lower mileage and you stand a good chance of carboning up your valves.

[perkj]

Running 87 will just mean your LR3 won't achieve its HP/Torque numbers as stated by LR. A lower octane will mean your engine timing won't advance enough for top performance as the engine will ping earlier in the RPM band and thus the timing will be retarded by the computer to control the ping so you don't crack a piston.

Until the ECU/computer learns that you are running 87 and adjusts the ignition maps, you are opening yourself up to pinging and potential harm to your pistons as a result. If you do run 87, I suggest taking it easy on the throttle for an entire tank full (200-300 miles) to allow the computer to adjust. To accelerate this, you can disconnect the battery for ~15-30 mins to allow the ECU memory to clear and then it'll start to build the ignition maps straight from the 87 octane data.

87 octane is in no way "dirtier" fuel than 92, so carb build up is not an issue with newer EFI cars....this was only an issue when ignition maps were very limited.


In the end, the money you save on buying 87 will be lost in the engine not performing optimally and thus getting a worse MPG.

The LR3 V8 is a 10.5:1 high compression motor, which is the primary driver of its requirement for 92 octane.....87 octane motors will be in the 9.x:1 ratio (unboosted)

[Disco Mike]

If you can't afford to run 91 plus octane in that engine, sell it and buy a V.W. or something that burns 87 octane.

[Mack73]

Originally Posted by Disco Mike

If you can't afford to run 91 plus octane in that engine, sell it and buy a V.W. or something that burns 87 octane.

I understand your point, but you know that german manufactures spec premium (including VW) right? Head to Japan or Domestics if you want engines designed for 87. Although I'm sure that with the switch to turbo's that all manufactures are doing, there probably isn't a manufacture that doesn't recommend premium for at least one model.

[Chris-bob]

High-octane fuels only become necessary when your engine has a high compression ratio.
"High Octane" is not synonymous with "good" or "better", and does not mean that it is better for your engine!
All gasoline, regardless of its’ octane rating, have pretty much the same amount of energy per gallon.
Octane is NOT a measure of power but of the fuels’ resistance to ignition from heat. A higher-octane fuel, under identical combustion chamber conditions, will burn slower.
The piston, quickly squeezing the fuel/air mixture into a small space, can generate enough heat of compression to ignite the fuel well before the spark plug fires, with unpleasant results. If the fuel prematurely ignites while the piston is on its way up, the burning of the fuel, in conjunction with the rising piston, creates even more pressure, resulting in a violent explosion. This explosion is equivalent to hitting the top of the piston with a very large hammer. If you want to be able to see through the top of your piston, ignore those sounds that are usually called: "pre-ignition", "ping" or "engine knock".

What we really want is a very rapid burn of the fuel, not an explosion. And we want the burning of the fuel to take place while the piston is in a better position to convert this pressure into productive work, like on its way down. Think of this burning as a very fast "push" on the top of the piston. Despite the violent noises you hear from some exhaust systems, it really is a rapid push on the top of the piston making the crankshaft go around, not explosions.

So that we can ignite the fuel at exactly the right time with the spark plug, instead of from the heat of compression, they put stuff into gasoline to keep it from igniting prematurely. The more resistant the fuel is to ignition from the heat of compression, the higher its octane rating.