I know its not an answer to your desire to track your Cayman, but have you considered a dedicated track car? A 924S at £1500, and £500 of mild preparation will give you a good fun tracker. Failing that, try joining one of the track-day clubs. They give you ride an drive access to a number of tasty cars without risking your own.

When you look at the economics, remember that tracking a road car adds significantly to maintenance costs and wear & tear. Tyre wear, brake wear, a bleed & and oil change plus one-off insurance could easliy run to >£500 per event. Four of those will pay for a cheap track rat...

SS7

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Carrara white pauper's 2.7
Snickers wrapper in the door bin
Flies on the number plate
Church's scuffs on the kickplate
'Goodwood' umbrella in the back