03-10-2019, 06:27 PM
The purpose of the inner spring isn’t so much to increase the spring rate. It does but you could do the same fitting a heavier single spring. The inner spring damps the vibrations in the outer and delays valve bounce. A standard spring will “bounce” at around 5000rpm, perhaps a little more. Doubles are good for as high as you’d want to rev an Austin seven. So, unless you want a high revving engine there isn’t any advantage.
Alan Fairless