When I put the SR20 engine into my car do I have to buy an upgraded clutch or could I still use the stock clutch on the KA engine?
You cannot use the Stock KA Clutch as they are different size and have different input splines.
You would need to get an Aftermarket SR20DET Clutch.
What’s wrong with your clutch? why do you need to upgrade it?
if it’s slipping badly, Bomex is selling a used SR Exedy Organic clutch for a very reasonable price. PM him about it.