So I installed my Factory Pro V-Stacks yesterday with the help of another forum member. It took us about an 1.5 hours with frequent breaks, not too bad at all. I did not have it dynoed, but my impressions are good. There's noticably more throttle response, especially around 8K-9K, but its not until 10K-15K do you really feel the difference. It pulls so much harder through the power band. For $200 (well..I got mine for $160 heh heh) there isnt a better mod for HP.