RE: Break in for racen
Some good advice here..... follow it.
the 8x6 is what Id be using for break-in. Maybe a bit less prop to start with.
Just for reference, my TT40 pro engine break-in proceedure (for 424 q-500 racing)
- I use a 9x6 clipped down to 7.75" diameter. Engine goes on the test stand running at 17,000 rpm, clean 2c while slightly rich (but not cold runs at temp and rpm at the same time). Goal after 10-20 minutes running like that is an engine that then turns 16,500+ peak ground rpm with the full 9x6 prop, and can be launched just over 16,000 with no concerns.
Are you saying you race the 25/28 engines with a 9x7 prop ?? Thats quite a bit heavy. Those little engines really should turn up over 14,000 to produce any reasonable power. If you are loading them to achive quiet... thats another story.
Loading the engines like that and only 10,000 rpm is just hurting the engines - they are struggling, and you folks are probably running them very rich to compensate. My quick thought on the situation is THAT is why it took 2 years for any reasonable performance stability/break-in to occur on your existing engine.
Bob