I have a Supertigre 75 which in a cowled TF P-47. It has been propped with a 14X6 which is well outside the manufacturers recommended maximum of 12X8 (att). The reason given was to slow the airplane for landing and to keep the engine speed down while breaking in. I believe this will prevent the engine from unwinding and breaking in properly. Would this not also cause overheating? My spidey sense tells me this is a bad idea....

Thx from SC!

Trust your Spidey Sence

Personnally I don't believe in using "Break In Props",, Ford or Chevy doesn't give you a Break in transmission, they just say take it easy fr the first few hundres miles

I run the prop I'll be flying it with and just run it rich for the first handful of flights before I start really ringing it out.

You want the engine to make some heat when it is breaking in. 'Break-in' props are usually smaller, to let the engine wind up but with less load. Keep the engine slightly rich, use a prop in the recommended range, and increase the diameter by one size/reduce the pitch by one size, if you need to control the speed of the airplane.

The load on the engine would be similar with 12x8, 13x6, and 14x4. I’d probably start with a 13x6 and move up or down from there after some test flights.