Mildly facetious question, I am assuming its primary purpose is to muffle noise from the engine, but I'm also curious whether there's any other purpose. I've discovered that the engine cover is responsible for the majority of unpleasant noise from my engine - resonating as the engine vibrates. I've removed the smaller of the two covers (nearside, the one shaped to look like it's skimming the exhausts from each cylinder) and now I hear only good, engine speed/load related noises, healthy. So, the question really is, am I doing any harm running without this cover? Is it important for keeping heat away from the underside of the bonnet? I'm considering getting an engine blanket (http://www.noisekillergb.com/product_details.asp?ItemID=91) in place of the plastic cover - see if I can damp out some of the remaining harshness - any thoughts/warnings?