Skat-Trak’s Yamaha impeller is recommended with a 13/19R Swirl* or 13/21R 155-61-22 Swirl** pitch in any 155mm pump. This is recommended for a stock Engine only. If you have modification to the engine and watercraft, please give us a call so that we can recommend you with the correct impeller application. *Suggested for maximum bottom-to-mid range acceleration gains.**Sugested for maximum top speed gains.