The only thing I have ever used in my SRT8 is 93 oct when it was Stock or with the blower. Now, the R/T has more compression than my SRT8 does so I figure it will be best to use 93. The VVT does make a differance so the 93 thing could be wrong on my part. Has anybody noticed a differance in performance using 93 over 89 in the R/T's???