Well nornally for cars with low mileage 5-30W should work..if you are talking about car with high mileage with worn out pistons and oil rings then 10-30W will work as it is more viscous at the higher temperature end..It is for regular cars,..if u are talking about high performance sports cars or the ones with diesel engine then it could be different,, It does not matter how many valves do you have in your car.. I am not sure there is any car with 4 valves..for a 4 cylinder car there has to be atleast 8,,4 intake and 4 exhausts

Good luck and have fun