well, Im not sure, because that tach I installed started to go crazy. But I have to say..... by listening to the engine with the 17p aluminum, and the 21p turbo prop I tested the 19p viper sounds like I am in the pocket. I will have to investigate the tach in the spring since it's all winterized now. The previous owner said 6000 rpms with the 17 he had on there. I have no idea why he would run that prop??? The hole shot is crazy fast, and the speed up to 40-45mph is almost instant. makes me curious what the viper 20p would be like. 53mph full tank and two adults.