This is my first post and visit to what appears to be a great and knowledgable website. A yank from the USA West Coast has a question. I'm a twenty year Merkur XR4Ti owner (two of them) and have only used them as daily drivers until now. I'm currently starting a restoration on my current one and it seems that my Merkur really wants to be a Cosworth. Not many real Cosworths make it across the pond, but many of the parts do. Trouble is sorting out what they are. I'm building the car for the road and the occasional slalom or track day, so I wish to improve the suspension but still keep some road comfort and clearance.

I have access to some genuine Sierra Cosworth (3 door) rear springs but no idea of real specifications or what to expect from them. They are roughly 300mm long by 125mm diameter unloaded compared to stock XR4Ti springs at about 380mm and similar diameter. Although not side by side, the material thickness appears thinner on the stock Merkur one. The Cosworth springs are black, look almost new, and have 3 identifying painted dots on each (pink, green, and red). Can anyone one help me to know what I might have here? The differential mount, dampers, and bushings will all be upgraded.