So I bought a new tach the other day, and checked one of my new For a .049 engines. I had the smaller blue prop they sell. It is around 4.63" but I am not sure on the pitch. I am leaning toward 3 but it could be a 4, waiting on clarification as I do not have a pitch gauge. Well, the little ******* was spinning 36,000! Pretty good I think. More testing to come, but I like that number. Fastest engine I have ever had. (other than my Nelsons)