Ran the KA100 since December of 2016, great engine package. Blueprinting helped slightly (it will with any engine) but the stock piece is not far off at all and will be fine for someone entering 2-cycle racing. We ran entire season (12 rounds at GoPro) on one engine (had a stock engine to practice with), no piston or ring replaced– it has over 20 hours on it and runs with any of them. As with anything, fresher will be stronger so rebuild as you see fit. In short, great economical engine that really does create a very competitive class.