Good topic. Always valid in motorsports.

There is another way to police legality of cars in the club. Instead of "looking" for illegal cars, which is very difficult, I would not allow them to become illegal in the first place. This is how I would do this in my club:

When your car is teched for the first time, or when you're the new owner of the car you get a list of things you must check for legality in a given class. Each item on the list will have a fine fee associated. You check your car and sign the list. In case you get caught the first time you pay the fee, plus all your points are removed. Car held as a bond until you pay the fee.

On the second count your car is taken away and auctioned off. Proceeds from the auction are divided and send back to the participates of that race as refund money, or credit towards next race.

Problem solved. There would be less cheating.

Also, it would help to capture sector times in order to filter cars (possible candidates for impound) that are going faster than physically possible.