When i got my manual i never thought twice about putting 93(top grade in my area) octane in it and im not sure how but i thought it was required even though the cap and filler door doesnt have any octane requirement on it i can find. Then i was reading some random thread, cant remember which one where everyone was talking about how they were using 87 octane and im like, i can use 87?? Just to be sure i yanked out the manual for my 2009 and it has different octane requirements, 87-89 for auto and 91 for manual. so i still need 91 but now im curious why? Is there a factory tune difference in the earlier challengers or do autos come with some sort of octane adjustment tuning?