What octane gas do people use in their XJ8/XK8? Can I use 87 with no ill effects? I run 87 in my '91 VDP with the 4.0 straight 6 and it does fine, the engine management simply retards the timing to accomodate the lower octane gas. Will my '99 do the same? Thanks

 

It certainly does in my car. I have run 87 in it since forced to 2 years ago by a gas shortage but you will find the forum members about equally divided on the subject. After careful evaluation I did not find any difference in MPG or throttle response but neither do I drive aggressively.

Jaguar obviously requires premium but that is more from a marketing issue in order to be able to advertise the horse power. Obviously, the car will not preform at top efficiency at the high end of output because of retarded spark advance.

Personal decision as far as I am concerned.

 

I run 94 in mine. Once in a while 91 w/0% ethanol.

 

Agreed, it is a personal decision.

It should be noted that seldom does anyone really wring the absolute last bit of performance out of their vehicle. At least, not for extended periods of time. But, the choice of octane rating is a full time commitment. For example, filling with premium on every tankful so that 2 gallons of that tankful is available for the one sprint of that tankful, and so that the ECM stays tuned to premium for that sprint.

 

Thats what knock sensors are for. I run whatever I feel like putting in it, usually 87 octane. She does get premium (93) from time to time.