I would agree that this is not a project to be taken lightly. A thrown blade could easily seriously injure or kill someone, if struck in the wrong spot. The suggested 2500 rpm produces nearly 30% higher centrifugal blade forces over 2200 rpm. I do not know what the factor of safety is on these parts, nor what condition any one persons equipment might be in, but I wouldn't want to be anywhere near a helicopter that far past its never exceed rotor speed. If the rotor shed a blade at some 2500 rpm that thing would be coming at you at nearly 100 feet/sec. How would you like to take that to the throat tip first?

Also, for reference, my Vmax7 hits 2200rpm at the head all day long with 6 degree grips (24860 engine RPM, at 11.3:1 gear ratio). When I first ran the motor and tached the head speed, I called up Paul at LMH to ask if this was ok, since the original documentation stated never exceed of 2000rpm. Paul also told me that 2200 would be all right, but not to go any higher. I usually tach my LMH before I put it up and set the needle to keep the head speed below 2200. It flys with plenty of authority with around 2100rpm head speed.

My recommendation for using an alternative engine would be to set the max throttle position such that max head speed is where you want it, as notasme suggested. This would allow you to set the needle as needed so the engine runs correctly, but still would guarantee you don’t accidentally over speed the head.

For what it is worth, and play safe!

Spiro