There is not much you can add to a tube to improve its performance. If the mouthpiece agrees with you and the inside volume of the tube suits you, your biggest steps forward will come from improvements in your darts. If you're handy you can start making your own matched sets. When competing regularly, I was buying fifty caliber cones in lots of two to five hundred and then sorting them according to size (fit) using a drop test. Each cone was fitted to a standard shaft and loaded into a horizontal barrel. Then with my finger closing the mouthpiece, I'd flip the barrel quickly to striaght vertical and count the seconds it took to leak enough air to escape out the bottom. Early on I got some false results because I failed to notice a few cones that were egged slightly. A good fit can take several seconds to clear the tube.