add the option of venting your engine oil tank and let your motor breathe, there is a little known passage from the trans top to the oil tank in the bottom of the case, we have sold over 9k ventilators this is just a slicker and easier way of doing it with our QA top cover , two options, brass fitting and a rubber line with filter, or all out -6 an fittings and braided stainless steel cloth covered hose with filter on the end, easy install with the QA cover