I am fitting the st170 valve springs to my new zetec head.

Question there are two differant lengths of spring. There is a difference of around 2mm.

The zetec is the same inlet and exhaust.

For any one wondering the st springs hav a thicker coil by 0.3mm.

Instinct tells me the longer ones are for the inlet to give extra clamping force on the bigger valves but this is a guess, any ideas ?