yup, clutch springs have a lot to do with the way your engine and car perform.
you said you have heavy springs now? well they let the engine rev up to like 10,000 rpm (estimate) before the clutch shoes open and engage, so the engine is making more power which is why youre spinning the tires the whole way down.
if you had soft springs, like I assume you did before, the clutch shoes will open at 6000 rpm (estimate) and you wont spin the tires a much. this is good if your engine.
thick springs give you more low end.
soft springs give you more top end speed.