As I remember about a 15 degree F drop in Ambient temperature is roughly equivalent to 1 point of octane detonatoin resistence. What that means essentially is if your car doesn't ping on a 90 degree day with 93, it won't ping on a 40 degree day with 89. Of course variations in heat absorption and transfer underhood skew thingas a bit, but in general, that's the rule of Thumb.

Max PSI, I can relate to both you and your Dad; My 10PSI '00 SI, shares the garage with my 70 Charger R/T which runs traction limited 12.30's @111, The new 508" motor should put it in the low-mid 11's and maybe high 10's with a 175 shot.

I love all my toys but the Si is sooo easy to work on and still get 28mpg, the Charger can get 14 on the highway. I got to say the import crowd around here does show a lot of respect for the Dodge, must be the F&F thing or maybe their dads were muscle-car nuts too. I got to say that no 4 banger I've ever heard sounds as good as that solid lifter 440.

Wize