<VV> Valve rotators

[Daniel Monasterio]

    This morning, while disassembling the 110 Hp engine I took off from my Rampside a year ago, I payed attention to the exhaust valve rotators. When I rebuilt this engine, years ago, I installed those valve rotators just because I had them at hand and had been readed that were used on FC engines but, have never known why. I just know that they rotate the exhaust valves and it is good on FCs but have no idea on real differences or advantages depending on engine usage. I have not enough light on my old brain to understand why valve rotators on FCs and not cars. It should be a technical reason but, can't find it. 
    Do somebody in the group have a better brain lantern than mine ?

    Thanks in advance for any light

    Daniel Monasterio