I will be using my new Aero.40RE lite engine this spring and the instructions say not to use more than 10% nitro. I live at an altitude of 5000' and have been using 15% nitro in all my OSLA.25,.40 .46's, SilverFox .40. OS,40fp's for several years to get a good needle and performance at my altitude. Would it be detrimental to my new Aero.40RE lite to run 15%nitro?

Hi Jerry

Quick answer is  no, there is nothing wrong with using  15%  20 25  or  whatever you need.   My  engines are designed to make good HP on 5% fuel, we routinley use 5% at 1100 ft in Atlanta, And normally end up using 7.5 or 10% in the hotter summer months.
Where many run into problems is predeterming they need to use high nitro fuels and use them to start. ie  guys in  sea level states  start off with 15% in March and wonder why the plane will accellerate going uphill.  People  using too much nitro has caused many problems for themselves .
Just use whatever nitro you need to help the engine run properly. and it is perfectly normal to use more nitro at higher elevations.

regards

Randy