That's an 11 year old reply... I think they sorted it out by now.I put f5.9 on my Savage and runs good and was easy to tune only thing I ran into problem was I had to raise motor mount 1/16 so bell didn't hit brake discs and I moved the gas tank out a Lil bit cuz it was pretty much touching the engine and it has great power I personally like to keep hpi parts on hpi trucks but other engines are fine