The advantage of a 4V over a 2V is when you stomp it the secondaries kick in with the 4V. Regarding the add-on's you aren't going to get much to help with the hp without it being noticed. Changing out the heads to some better breathing ones will help some, but those Clevo heads are not laughing stock. The intake manifold is one of your restrictive things that could add some breathing room and hp, but an aluminum intake would be noticeable. MSD ignition would add ponies, but obviously that big red box would stick out like a sore thumb. Long tube headers with collectors would improve performance along with either an "X" or "H" pipe, but again, noticeable. Internally, flat top pistons and roller rockers would add a lot of hp.