[Snake2998]

Be careful of assuming that the rears do very little braking. In a Cobra with a low center of gravity and rear weight bias (Say 48% front and 52% rear or possibly more rear bias) and wider tyres on the rear than the front the proper brake bias should be something like 59% front 41% rear compared to 68% front and 32% rear for a Jag XJ6 - the system you are possibly using.

If you don't make sure that the rears contribute the extra 10% of braking compared to the Jaguar setup you will be losing out on a lot of braking so you have to be careful that you update the system as a whole. Using this extra braking at the rear could lead to overheating in the inboard system in continual heavy use (like track use) so it is best to fit ventilated discs at the rear - preferably with curved internal vanes. Too little bias to the rear will cause early lockup of the front brakes causing reduced stopping ability and possibly instability and squirming under braking - too much at the rear will cause the car to spin and possibly crash so make sure you get the balance right with proper design of master cylinders and disc caliper combinations and careful on road testing.

Disclaimer - the above figures are based on my own calculations and should not be used as a basis of your decisions. Get a genuine expert to design the system for your car using it's individual physics and it could stop much better than an unbalanced system. And stop much better than many kit Cobras whose brake system come unmodified from some donor car.