Just fill up your gas tank with the new gasoline and tune your ears for pinging (or engine knock or whatever you want to call it). If you hear any pinging, retard the timing a hair and try again. Repeat until you hear no pinging at all operating conditions, including WOT. I have heard messing with the timing with the 392's is not fun, but you may be lucky and hear no pinging. I would guess with only 9.25 compression ratio and a hemi head, you will not ping if you run the stock timing adjustment. Another option to stop/reduce pinging is to run a colder thermostat, but this is generally not a good idea. D^2 Quoting Philippe Courant <accf-club@xxxxxxxxxxxxxxxx>: > Hi, > i just wonder what are the different octane number gazolines you have in > USA ? I know that the US octane number is different than french (RON) > number and seems to be (RON + MON) / 2, so a 98 RON (= 88 MON) would be > a 93 . > At this time i run my '57 Imp with unleaded 98 RON (so 93 for you) and i > want to switch to 95 RON ( = 90 US gazoline, don't know if it exists..). > My compression ratio is 9.25/1 so what is your advises ? > I've found a table in the middle of > http://www.faqs.org/faqs/autos/gasoline-faq/part3/ (paragraph 7-2) but > i don't know if the "octane number requirement" means US or another > octane number. > > -- > > Philippe COURANT (Pau, France)- Webmaster des sites ACCF et C-I-F > Imperial 1957 Crown convertible > Buick 1996 Roadmaster wagon > > - American Car Club de France (ACCF) : http://www.accf.com > > - Chrysler Imperial France (C-I-F) : http://www.ifrance.com/c-i-f > > - Cadillac " Standard of Excellence " : http://www.ifrance.com/accf-cad > > - SportsCars : http://www.ifrance.com/accf-sprtcar > > > > >