I have been using regular (USA AKI 87 - 92 RON) on my xj6 III.
Is it acceptable ?
I hear no knocking at all.
My mechanic told me to use Premium but seems a wast e for me driving at 15 to 16 mpg.
I use premium on my 96' xj6.
thanks

 

I've run the V12 on regular before without pinging but I just keep premium in it because its not worth the chance with such high compression ($5 per tank?).

The 6 cylinder is like 8:1, I can't really see why it would need anything more than regular and the handbook for my '87 says to use 87 Octane.

Needless to say, use top-tier gasolines with good detergents and you should be fine on regular.

 

I think the US cars got the 8:1, but for Europe it was 9:1. In the old leaded-petrol days most drivers used "4 star" which was 97 RON, but you could buy 99 RON at some stations. Now the main fuel is 95 RON, with 99 RON available, (both unleaded, of course). I always ran my Series 3 on 95, and do the same with my X350. No point in spending money if you don't have to.