Does anybody know a resource for info on diffs and ratios in a 2WD Sapphire?

I drove at Castle Combe yesterday and my car is hopelessly under-geared there but perfect at Brands.

It is time to start investigating what is in my car, and what I can put in my car. So I need to know where to start, what markings I should look for, and how to work out the relationship between top speed engine power and diff ratio.

Thanks all,


Charlie