                                    The valve guide is a very important part of the VW aircooled head.
                                    The guides job is to do just that "guide a part" and in this case its the Valve.
                                    The guide must be strong, straight, and have good wear characteristics.
                                    The guide cannot come loose at anytime, so proper installation is crucial.
                                    There are several different types of guides, the most common ones are shouldered guides
                                     and racer guides.
                                     I am not a big fan of racer guides, at least not in daily driver heads.
                                     If you are looking for some flow or CFM, then racer guides are great,
                                     but they are typically shorter in overall length.
This means there is less support to the valve and will not GUIDE the valve as good as a stock length, shouldered guide would.
Yes, you will lose some flow but isn't it worth the peace of mind.