I have a 2001 VDP. I ALWAYS make a point of putting 94 octane gasoline in my cars, however, the only gas station in my region (Sunoco) that offered 94 octane has changed to another line of stations (Husky, Pioneer, etc.) that offer 91 octane as their highest premium level fuel. I know the Jaguar requires a 'minimum' octane level of 91, but I always like to take things a little further, logically or not . Would it be at all beneficial to add a little octane boost to my Jag V8's fuel tank when I fill up or is 91 totally sufficient?

 

No. Complete and total waste of money.

 

Modern engines with electronic control have 'knock' detectors which detect fuel pre-ignition and back off the ignition timing until knock ceases. However there are presumably limits to this hence the 91 Octane limit quoted by Jaguar. So that explains why 91 octane is OK and you don't need octane booster, but if adding some gives you peace of mind, you could consider it money well spent, even though it is not strictly necessary.

If it was me, I would see how I get on with the 91 octane. You are unlikely to damage anything. Here in the UK the fuel companies try to sell our 97 octane over the standard 95 by saying you can get more miles per gallon. I tried this and it seemed to be true, but not enough to compensate for the extra money spent, so I am back on 95.

UK octane ratings are calculate different to the US by the way.

 

As Fraser stated U.S. and Europe Octane numbers posted on the pumps are different.

Here in the U.S. we use the (R+M)/2 method. In Europe they use the Research Octane number, which as a rule of thumb is about 5 points higher then the (R+M)/2 method. 87 research octane (RON) has the same anti-knock ability as 87% isooctane and 13% n-heptane. The Motor octane number (MON)is not quite so straight forward. This number is derived while putting the fuel under a load, like it would be in an engine to arrive at its MON. So take these to numbers and avg them. That is the number posted on the pump.

 

Pale-

That's a good description of the rating process and the differences between N. Am and the rest of the world. There's untold myths and confusion over the two different rating systems. I have no idea why we changed ours back in the 70s, but too late now.

I suppose the false belief that more octane= more power, better mileage, faster starting, smoother idle etc. is universal though.

 

If you read the bottles they say 2-3 points increase. That does NOT mean it will take your 91 oct to 93 or 94 but 91.3 or 91.4 for a 20 gallon tank. You'd need ten bottles to raise it to 94 octane.
However I've heard the Torco fuel additives do have a considerable effect on the octane rating.

 

Layman’s terms...

Octane rating is the fuels resistance to ignition.

Higher octane fuel does nothing good as far as HP or MPG. Hell it can hurt you HP and MPG!!! The only thing it will do is allow you to run higher compression, or advance your timing, to increase HP. If your car was designed to run on 87, then run it on 87 or waste your money. The only time you should ever run higher octane is if you’re tuned for it, or experience pinging, (detonation). But on a stock vehicle those are signs of something else going wrong.

As far as Octane boost, like they said above, waste of money unless you’re just using it as a fuel system cleaner, but there are better products for that as well. I keep ½ jug of Octane boost in my Harley for really hot days and I’m stuck in traffic, but again that’s due to detonation.

 

I have a question: 2003 XK8......I normally cna't hear it, engine knock that is unless I am like next to a wall or barrier and on acceleration I will get an engine knock (Pinging). I am using 91 octane fuel. Is this slight ping normal?

 

Very true, they usually say the raise th octane points by 4-5, which equates to 91.4-5.

An octane rating of 1, is actually .1, so it does absolutely nothing except cost you $6-7.

Do not buy into hype, you cannot clean injectors or unstick valves, clean throttle bodies from a bottle.