The 'E' Type Forum

I understand that SA numbered V12 engines are 9.1:1 compression ratio. At this compression ratio should we be using 95 or 98 RON Octane fuel - I think 95 should be OK but some say 98 to be safe.

Lets assume ignition is set to standard by the handbook and not advanced.

Thanks

Garry

Handbook says 98. Like you I wondered about it. Used 95 if was 98 n/a, no side effects. My compression was >160 psi.
SA or SB. The "S" is the compression ratio (L = low, S = std, H=high). A and B are the piston/sleeve manuf'g tolerance.

Hi Colin - yes I found the answer in a different V12 handbook - but that was all written about 50 years ago and was thinking did it still apply with modern unleaded fuels.

Engines, both old and new, that have compression ratios in the 8.?:1 can run happily on our 91 unLeaded so I would have thought an engine like an older V12 with 9.1:1 ratio would have run on 95 Ok.

If the 9.1:1 V12 needs 98 Ron, surely with a HE engine running up around 12:1 ratio, 98 Ron would not be good enough without additives but I guess the ECU can compensate under high loads and retard spark.

Oh - are you a member of the Jaguar Drivers Club of Canberra?

Cheers

Garry

I ran my Pre HE V12 on 95 Octane fuel with no problems.
I reckon it did run better on 98, but lack of availability dictated using 95 most of the time.