Hello!
Well, too much nitro in an engine not made for "high" nitro contents will only make it produce less power, due to the wrong compression ratio.
Nearly all sport engines are "made" / set-up, to "like" 0-15% nitro, this is a well known fact among every flier that has been around for some time.[>:]
In Formula 1 pylon 10 years ago or more, 50-65% nitro was used but this was in engines that had their combustion chambers set up to run on such high nitro percentages.
Over 15% nitro in nearly all sport engines will only make them produce LESS power. That's a well known fact! This due to too high compression inside the combustion chamber.
There are some fourstrokes like the Saito and Y&S that can handle more than 20% nitro but they are the exception to the rule.
Running ordinary OS ,TT or Magnum engines on more than 15% nitro is just waisting money, getting less power and shorter engine life...and probably most important ...risking the aeroplane due to the engine being very hard to set!

Regards!
Jan K
Sweden