Limit 5 mins max WOT???

Reliability and longevity. 

Since you aren't in an auto you can't pull over to the curb. You want longevity and solid reliability out of the engine. If you didn't and always work out of the Mfg's limits then lots of people would be buying new engines or crashing.

This question has come up before.  https://www.rotax-owner.com/en/general-tech-discussion/8424-what-is-the-precise-reason-for-the-5-minute-limit-at-5800?start=5   I do not believe I was answered in a definitive way

Brake Mean Effective Pressure (BMEP) is the relationship of amount of torque produced to the displacement of an engine. Due to metallurgical constraints modern engines can run up to about a BMEP of 180psi.  A Rotax 912 has a BMEP of 165psi.  A Rotax 914 turbo is 190psi. Every engine has limits. Like Roger says, you can't pull over to the side of the road.  

Thanks for your quick replies. The question arise me reading about lot of developers of turbo systems for Rotax, (don´t be confused, I have enought with 100HP....) and even 912 and 914 share the same block, pistons, heads, valves.... so I don´t quite understand the limit for 5 mins while others claims for 120 or 130 HP with same engine block.

Kind Regards, Marcos

I believe you might be misunderstanding the specs.  The 5 min limit is for 5800 RPM.  There is a max continuous rating RPM of 5500 RPM.  In the case of 5800 that is assumed you have a inflight or constant pitch propeller and can set the load.  If you are dealing with a fixed pitch only you should never set it to 5800 as it will unload the engine too much and could lead to other problems.  

Aircraft engines were not really designed to run at WOT all the time.  It is best, for fuel economy and for wear in the engine, to fly as much as possible in the 4800 to 5200 RPM range with this design.  It is the area of peak torque for the engine and this will give you the best throttle response and give you the best engine life.  

Aftermarket parts sellers make a lot of claims however they are not promising you will get 2000 hours and are not saying you have dependability over the long term.  Yes you can squeeze more HP, but it is at a price. Performance claims are fine and if you want to spend a lot and get performance that might be nice, just don’t expect 2000 hours at that kind of power setting.  Many of these builders actually remanufacture the block, crank and put in special pistons....and lots of other mods, so it is not the same engine in the end.