Hi,
Just got a 1985 XJ6 with the European high compression 4.2 with 3.056 rear end. It's a barn find so I'm cleaning the gunk out of the tanks / fuel system right now. I'm going to do a whole thread later but have a quick question for anyone here or in hopefully in Europe where these are more common ( I think ? ). What minimum octane keeps the high compression engine running well ? I'll assume they don't like low grades like some older GM 350's I used to own but would like to get options from the experts here before filling her up for testing. I'm going to use non ethanol to prevent / reduce future rusting since it's not going to be a daily driver but would like to know how picky they are about the octane rating since the options are more limited.

Thanks everyone !
Cheers,
Brian

 

My '87 low-compression USA spec XJ6 ran well on 87 octane. I suspect 92 octane will be fine for your car. If not, a small tweak to the timing should do the trick.

Don't depend on non-ethanol gasoline to prevent fuel system rusting. Fuel tanks and lines were rusting long before E10 became a thing. One good idea is to simply store the car with tanks full.

Cheers
DD

 

They were designed to run on 95 RON, which is roughly equal to 91 AKI (i.e the system used in Canada/USA).

An engines octane needs decrease with temperature and elevation, so the same engine in Denver in the winter requires less octane than Houston in the summer.

 

HI Kudzu,

I run 98 RON in Melbourne.

I also fill the fuel tanks to minimise condensation (water / rust) if the car is going to sit for any length of time.

Regards,

Nigel

 

Thanks for the advice, I'm going to use 90 non ethanol for now and see how she likes it. Currently de-rusting / cleaning the tanks, about to flush all the lines then replace all but the vent hoses with low-perm as well as removing the injectors to clean out the "coffee grinds" that were making it past the filter. I'm taking pictures and will make a thread when I'm done. Hopefully by this time next week I'll actually get to hear her run instead of sputter !

Cheers,
Brian