is there a synthetic oil in 5-20 for 5.7 engines ?

I know that the 5.7 hemis with MDS require 5/20 oil. I will be getting some free oil changes from dodge and I need to find an oil change schedule I can use. I won't be putting a lot of miles on the car so the oil change times will have to be how many months between oil changes. the dealer said If I don't drive a lot of miles then change oil every 4 months. My question is, what is the best 5/20 oil for the 5.7 hemi with MDS ? conventional or synthetic oil ? Do they even make a synthetic in 5/20 ? I am not using an oil catch can yet & if I do add one which is the best oil to use for these catch cans ? conventional or synthetic and why is one oil better than the other for the 5.7 hemi MDS ?

 

Yes there is I've run both Mobil 1 and my favorite is royal purple..

High Performance Synthetic Lubricants and Motor Oil - Royal Purple