O.K, I read somewhere in the old R.C. mags that cox tested the engines for this, and they quit testing after 300 hours because it was still going strong. I also just checked the flight log from last year, I keep records for this purpose of engine use. The one Cox had 6.5, and the total for both I flew on was 17.1 hours, in 2006.

This is for the Cox engines only, and know the total is correct, and these engines are going into the third and forth seasons. 25% nitro, a bit more added castor to around 21%. Still going strong, so perhaps the cox last longer? Haven't had a failure as yet.