I was never much of a Fox fan, we flew goodyear and couldn't afford the Rossi's or Supertiger .15's and used the Fox with the slant plug, and they would be slow and wear out.(lean runs on high nitro)  Had to get the Supertigers anyway.  The stunt .35's we had to use for the slow goodyear, I bought a few, then they changed the rules to the LA .25. They are faster and smaller.  Now I am stuck with a bunch of slower 1950's slugs that I can't use for anything.  (mufflers don't fit on all of them)  I picked up a .15 BB and put it on a Sig Wonder because it needed noseweight, and I do like it.  It revs up like all the others with the turbo plug head I made up, and idles nice.  There is still hope for Fox I guess, they just need some new designs.