I've run my .11's and .07 and they are quite spirited engines with the right prop. I have found that the .11 will except the Cox .15 medallion head and run well. I have also used the glow plug adaptor sold by McDaniels R/C in the 1980's. The ball and socket reset tool for the Cox .09 work on the Gilbert .11 piston with excellent results. You just have to not use the receptacle for the Cox .09 piston.