I bought my C-320 in Aug. of 2018 (Limited crossfire with a wagon skin) in other words the C-320 has the same engine, transmission, and rear end as a limited crossfire.used high test as recommended in July I started using reg gas yes 87 octane after three or four tanks full and about 1000 miles, and after much research I added some E85, 3 gal to a tank full of reg. the power increase was very noticeable , by adding 33% E-85 every thing in the fuel system is safe, google it and ask people that race and want more power ,,no people that sell or just work on cars., one of my source's is a Ford engineer , one is a nascar mechanic, mercedes shop and others,,, power not gas mileage ,, maybe this is a cheap was to gain hp in the limited as well as the srt6 jim