TT engines are ABN not true ABC.

Secondly they are the most sensitive engines available in the market. If you change spinner/prop or any load on crank shat the performance will vary much. These engines are also very sensitive to dust and moisture, and if there is a dust layer in the air you will definitely lose some compression with these engines.

These all factors are due to internal metallurgy of the piston, sleeve and crankshaft material.