There are many different cam specs available so gains would depends on what you go for. You will get better gains the more you spend. For example a mild road cam will show a small gain compared to a wilder can combined with a few other mods such as a quality ported head and custom mapped will show a much bigger gain. Most people would say generally cost and effort wise you would be best to sell the VTR and simply buy a VTS if your only after a little gain. But I went and tuned a 1.4 so hay everyone to there own