I've always run Premium but my mechanic says he only ever runs Regular in his.
This would save $$ for sure.
Anyone else running Regular?

 

I run regular 87 octane in my X308 sedans. The knock sensors will keep the engine from damage and I just use them for casual driving.
The X300 also has a knock sensor as part of the engine management.(The XJR is a different matter)

My XKRs are different. I use Premium because of the SuperCharged engine and occasional 'spirited' driving.

Your mileage may vary.

 

always regular

 

i always run premium cus not only the higher octane rating but the other additives they add that aid in cleaning. it eliminates the need (atleast as much) for fuel system treatment and cleaner.

i can't speak for everywhere cus obviously petrol is different in US, AU, EU etc with different brands and blah blah blah.
here for example we have no such thing as 87.
or regular is 91 octane.
we have cheapy e10 (10% ethanol)
then there is "premium" 95 octane,
and then there is the top shelf 98 octane which companies also add additives to aid in keeping fuel system clean.
then there is the e85 which well unless you build and tune for it and plan on racing, there is no need/purpose.

i run regular 91 in my other car but always treat the cat to the top shelf 98.
its like you drink Jim Beam on the daily but on special occasions you pull out the Van Winkle

 

I run mine on premium as there is a “use it or lose it” campaign among some classic motorists in the UK , where higher ethanol content is evidenced in regular fuel. The Jag can use any of it, but my other classics wouldn’t all be so suitable.
Having run the Jag on regular many times, I was able to persuade myself that there was a tiny difference to how the car ran on very light throttle, and a tiny improvement in fuel consumption, favouring premium fuel each time. The consumption improvement was not sufficient to offset the higher cost however.

 

All AJ16 engined cars sold in European and North American were mapped to run on 95RON fuel. This equate to about 90 Pump Octane Number, which I believe is the way octane is defined in North America. If a car is run on a fuel which is less than 90 Pump Octane, it is possible that the knock control system will need to retard the ignition timing. It will be safe to run an AJ16 engine on 87 pump octane fuel, but it will probably produce more performance if run on a fuel which is at least 90 Pump Octane Number. I appreciate that 90PON is not a "real fuel grade", so 91PON would be the standard grade for an AJ16 engine

 

^^^ that is the good answer....
the reason i run the 98RON here over the 95RON is not due to the extra octane but due to the other additives they add that make it a better cleaner fuel.
but on that note i assume @XJRengineer would know, after adding your crank angle bracket does that make 98 a more viable option? is there benefit to higher octane values then?

 

Owners of cars with AJ16 engines can continue to use 95RON or 90PON fuel after fitting one of my revised crank sensor brackets. However, it is possible that there will be a performance benefit from using higher octane fuel, it depends on the exact compression ratio of the engine in the car, and other factors like ambient air temperature. There is unlikely to be any perfomance benefit from running a standard AJ16 engine, with my bracket, on fuels higher than 95RON or 90PON, as this is the fuel on which the engine was mapped to run. High octane fuels may have different "additives packs", which may have other effects on the engine, not directly related to performance.

 

I am a little confused: Is there a possibility of improved performance with a higher octane than the one specified in the manual with or without using your bracket?

 

If you do not have my revised crank sensor bracket fitted, it is most unlikely that using a fuel of higher than 95RON or 90PON will produce any increase in performance.

If you do have my revised crank sensor bracket fitted it will definitely increase performance, if you continue to use 95RON or 90PON fuel.

If you do have my revised crank sensor bracket fitted and use higher octane fuel than 95RON or 90PON, you may get improved performance compared with continuing to use 95RON or 90PON fuel.

I hope that this is clear.

 

Thank you! Clear as mud

 

Your knock sensors " may " come into play retarding the ignition timing on all cylenders when detected and commanded

this would decrease the power on this variable of consideration

So you have a balance factor

With the ignition timing advancing Andy Bracket you are closer to the critical point

Curius about your 10 degree bias bracket as a graph

Octane rating - Wikipedia

 

Hi Parker,
I'm afraid I don't know what you mean by "Curious about your 10 degree bias bracket as a graph". I only make brackets which advances the ignition timing by 5 degrees

Are you referring to the reference in Wikipedia, which confirms that MON is 8 to 12 units numerically less than RON for a given fuel. Taking the average of 8 to 12 as 10 and the equation AKI or PON = (RON+MON)/2, then rearranging these 2 equations; AKI or PON approximatety equates to RON-5.