With the quality of the petrol that we have today I don't think there is a lot of use for this. It was designed so that if you were in an area that had poor quality petrol you could retard the timing without needing to change the position of the distributor and therefore mess up the overall tune. The same thing could be done by putting marks on the base of the distributor that would allow you to move it a set amount and put it back again but it would be difficult to get a fine adjustment that way.
If you are running a lower octane fuel (than that at which you have already tuned your engine) you may need to retard the timing to stop pinging and if you are running higher octane you can advance (though this is not as critical as the vehicle will run fine without). Please note that if you have set your timing to the book then advanced it until you get pinging then bought it back until you don't you will be pretty much set up for the quality of petrol you tuned with. Any adjustments are then made from the known quality of petrol which is very much standard across Australia. Ethanol may vary this slightly but you should be avoiding ethanol anyway if you can.
Cheers,
Tim.
Snowy - 2010 Range Rover Vogue
Clancy - 1978 Series III SWB Game.
Henry - 1976 S3 Trayback Ute with 186 Holden
Gumnut - 1953 Series I 80"
Poverty - 1958 Series I 88"
Barney - 1979 S3 GS ex ADF with 300tdi
Arnie - 1975 710M Pinzgauer
Bookmarks