After our brake upgrade to larger Volvo 740 discs and Mazda RX7 alu calipers, we were not satisfied. The reason was not the braking capability, but the lack of ground clearence. Let me explain: the Volvo 740 discs have a less higher hat then the original Volvo 240 discs. This meant that we had to use a 20mm wheelspacers because otherwise the calipers would touch the rims ( not enough backspace). But with 20mm spacers the wheels however touched the fenders, so we had to use smaller tires resulting is less ground clearence, less then 5cm.
However we solved this problem by fitting solid Volvo 740 rear discs at the front.They have a much higher higher hat and now there is far more backspace and the calipers will fit without using wheelspacers. We had only had to make minor modificatios to the brackets to fit the Mazda calipers. Now we can fit the original wheels again and have more ground clearence. Ok, they are not vented, but I do not think this matters for dragracing. You only brake once at the end of a run, so I thinks they will not get that hot.