If you fit an cone filter without a heatshield then what fritzenburg says is true. The filter draws in hotter, less dense air from inside the engine bay and actually loses you power, as opposed to the standard airbox which draws cool air from inside the front wing. The BMC CDA has it's own built-in heatshield which gets around this problem, but you have to fit the cold air feed pipe and route it down to the front bumper to get the full benefit. Doing this a "force feeds" the filter with nice cold air at speed. This makes a real difference to throttle response at motorway speeds. I would lik