I have an interesting finding. I live in missouri and i've been using QT gas. I haven't been paying any attention to the octane that i was using. So Yesterday i just happen to look at the octane and saw that it was only 91 octane. So I stopped and drove around until i found a gas station with 93 Octane. WOW!! what a difference. my car seems to be snappier in the shifts and quicker on the kick-down. This my be in my head but I swear it made a difference.

Does anyone have any input on this???

 

Don, it is possible that you are seeing a bit of a difference. The 2.5L/3.0L motors are meant to be run on 93 octane gas and therefore the programming of the computer are set accordingly. When you run lower octane gas, the computer has to retard the timing to compensate. This will result in slightly less power. As for how much, too many variables to get an accurate number. So, you feeling more power from the motor is partly true, but is probably overstated due to the butt dyno.

 

Thx for the quick response.. that makes since then.

 

blah! QT and RaceTrac gas is for rentals only (and maybe the company truck).

 

GAS IS GAS!!! I use the lowest octane lol

 

i like to make my own mix, i use half 93 and half 87 and a splash of lime juice garnished with a lemon rind... great for a hot summer day

 

Not really

 

My personal opinion is that you will get the performance you expect from the octane you select. So if you buy 87, you'll get 87 grade performance, 93 gives you 93, etc.

Jaguar wants 91 minimum, and I listen.

 

Kind of like women.........................

 

I've been advised by Jag service manager to 93 during summer and switch to 89 when temperature falls below 50 degF. He said this eliminates any driveability issues. I've done this and can report no issues.

When I had rental x-types(during servicing of my car) I can tell they've filled it with 87 gas as the engine ran coarser and not as 'snappy' as it usually runs on mine.

 

A little input on Octane...

The X-type has a compression ratio of 10.3:1 to 10.5:1 depending on the year..That alone justifies the need for 91 octane fuel or higher, but not only for that reason.

Octane affects ability of fuel to burn, fast or slow...Low octane burns fast..Higher octane causes the fuel to burn slower...giving a longer sustain combustion process and not allowing the fuel to burn or pre-ignite before it's time, known as knocking or pinging, due to higher compression...Also High ambient outside air temps affects this, the fuel will tend to burn faster under higher heat and thereby robbing performance and may cause pinging as well...So it is good advice to find and use the highest octane you can in the summer for these cars.

The X and most other cars have what is know as pre-detonation sensors or knock sensors to determine if it is igniting fuel too soon by affect of either high compression, high heat or advanced timing..All this data is fed into the ECM to manage timing of the spark...There is a set of what is called OCTANE TABLES programmed into the ECM. The ECM will sort through the tables and set the timing according to Compression, intake air temp, and fuel type and try’s to keep the timing in a range of optimum performance for the engine. If fuel is used that is too low in octane for the given set Tables, the ECM will try and to retard the spark to compensate, hence, compromising performance. Low octane in High octane engines is just as bad as high octane in low octane engines. The margin or power band for ECM to adjust in is narrow..

So bottom line, use what is recommended and expect the best performance and mileage.

 

- good one!

This topic has been brutalized several times. For a great read with plenty of drama, check this out: http://forums.roadfly.com/forums/jag...8230497-1.html

 

Thanks for the right answer.

PS to Colt...GO JAYHAWKS

 

Lol there is a significant difference between octanes if your car takes 91/93. I can even tell the difference between some major brand gas companies. All of them being 93 octane.

 

Here in Australia they say min 95 ron - but I usually put in 98. I have no idea if I'm being duped here, but I am under the impression that it is better for the engine. Is this correct?

 

yes i do too aladamson. i have found that a tank of 95 ron gives me a range of 470 km whereas a tank of 98 ron gives me a range of 570 km or thereabouts. it did take a few tankfuls to clean out the 95 ron though as i dont like to see the tank get less than half full.

it seems to me that there is a slight edge in performance using the 98 ron over the 95 although this is very difficult to quantify.

of course the 98 ron is supposed to be cleaner fuel so in theory it should be better for the engine.

 

You weren't imagining anything. If your car's computer detects high Octane fuel, it changes engine mapping to take advantage of the better octane.

That is why I posted my thread, I wanted to find 93 Octane or use tose Octane boosters in a can.

 

Old thread revisited, and generally thrashed, but I always use 98 octane fuel in Australia or, if 98 is unavailable, I will toss in one tank of 95. My car has only ever tasted these 2 fuels.