yes cold air is more dense but octane is a rating for resistance to pre ignition based on combustion chamber temps before spark happens....like when u compress air it heats up ..... so i mentioned the octane because when its hotter than Hades the chance for preignition goes up alot because the entire motor and even the intake air is hotter so i might need either lower compression or higher octane ....but i could be all wet hell i don't know lol maybe somebody smarter than me can explain it better .