Which prop should I use if I hook up Sunny Sky 2212 980 kv to a 4s 5200 mah battery..

8inch.

8*4.5 would be the appropriate one. If you feel adventurous you can use 9", but keep checking the motors and esc for anything unusual. Also make sure your esc is rated for 4S, because most of the 20 amp esc's  are rated for 2/3S. And a 25-30amp esc is suggested.

5200mah would be large battery IMO, your AUW needs to be 1.3/4kg with the battery for a peppy flight. You can go upto 1.6kg which should be max IMO.

30 amp afro is what m using...

5200 mah multi star... Weight is aroung 400 gms

Thats rated for 2-4S so you are all good there. Whatever the weight of the battery is, you need to keep an eye on the AUW. So try the combo and if it works for you then its good enough for you otherwise need to reduce/increase AUW accordingly.

FYI: Some users even use 10" on 4S, but personally I dont endorse it.

I have used 10" CF props on 4S with the SS980kv without any noticeable heat problems. My AUW was 1.6kg. To add to what SideWinder said,
Just  because you can doesn't mean you should. I personally have been using 9/5 gemfan props without any problems.
The ideal prop would be the Groupner 9/5 E-prop, 4S.  

8-9inch 10 inch can be good for sometime but you would notice heating issue with the motor soon.

My advice..

Use 8 inch slowfly type or 9inch graupners which is same in thrsut as 8inch slowfly.
10 inches are useable but motor core saturates and consumes more current but performance doesn't increase. Obviously it feels more powerful with bigger prop because ure hitting motors top end with out throttling but due to gearing(props).

Quote from: pravesh736 on November 03, 2014, 03:03:17 PM
10 inches are useable but motor core saturates and consumes more current but performance doesn't increase

Exactly, you said what i meant.