In some coil spring apps a thrust bearing is placed under one side of the coil to reduce friction and you end up with a more efficient combo.

Has this ever been tried with valve springs? Slap me if I'm waaaay off in left field.

I have never seen a thrust bearing used on a coil spring... What application?

Rotators on old exhaust valve springs, that's all I've seen. Although I swear I did actually see one hack shop put them on the intake valves. Maybe he trained at cobra?

There's a BBC head that uses rotator on both intake and exhaust valves

I've seen them on coil overs
On the fronts

Under clutch springs for snowmobiles...LOL. But that's because these springs twisting/turning is part of the force used to tune the clutch. These clutches twist open and close.

BTW: Valves/springs/etc rotate without rotators/bearings/etc.

http://www.youtube.com/watch?v=WtqDHJDN79w&feature=player_embedded

Struts. Front ones.

I understand very well they use a bearing on top of front struts so the car can turn. But that's not what I got out of his description of a thrust bearing on the coil spring.

Haven't run across it but his was a sbc, one head they were on the exhaust, the other on the intakes.

Oh, I thought you took valvespring and brought in coil springs in general. My bad.

If you did mean coil springs in general, then I'll remain with my snowmobile clutch examples as others and I (in some clutches) use bearings in direct contact with the coil spring.