the k&n intake system is designed in such a way that wen you do close your bonnet, the actual bonnet becomes the air tight lid on the system, that is why around the actual pod is a plastic box and some rubber lining. They do not need a lid because the lid bonnet compensates for it. if u are really worried about heat, yes heat shields are great. There is a password jdm one which is placed directly infront of the engine and there is the radiator cooling plate aswell
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