There are several mechanical advance curves. which one your car has is dependant on several factors. Where was it's market? Which Transmission? What year? Was the dizzy swapped at some time? The only way to be sure is to lift the breaker plate and look at the stamping on the advance cam (flat rectangular plate with 2 slots the advance weight ride in) The number stamped on that plate is the distributor advance. Multiply that by 2 and you get the crank advance. So if you have a 7.5 distributor, you have 15 degrees crank. Set the your initial timing at 18 and you've got 33 total advance (pretty safe at normal compression and pump gas) If you have an 11 dizzy, you have 22 degrees at the crank, set that at 18 and it I'll rattle itself to death, quickly. If you can't run more the 7 degrees initial, you probably have a 13.5 dizzy (U.S. Smog equipped). Which one is best? That can be argued. My preference is the lower mechanical advance numbers of the "Euro Distributor" as marketed to the U.S. When I had my EI dizzy built, I had Gary set it up with a 7.5 advance. Sot I time 17 for regular and just a hair under 20 for premium. If my compression was enhanced, I'd have to lower those, or run race gas and run a high overlap cam. Nissan, in it's smogging wisdom, equipped the U.S. Market Roadster ( a sports car!) with the worst possible dizzy, a 17.5! You had to time that at TDC! Absolutely the lousiest idle and low-end performance ever. That's ok, cause we all fixed that with the pre smog 7.5 dizzy!