In the manual for my gsr it says to add 1.24 gals coolant, and 1.24 gals water. For a supercharged car what would you guys suggest? I was thinking 1 gal coolant, 1.5 gals water. Thanks in advance.

i'd just keep it the same. the best you could do would be to get a larger/better radiator

JR recomends 50/50. ive used 50/50. we both had no problems with 50/50. you should have no problems with 50/50.