if you are not racing get a XTM 24/7 Pro, it is as well a SH engine but it will outperform the .21 bottom and top end, as well the XTM is easier to get warranty on as well.............though i have found the SH engines are very picky with pipe selection, some pipes really hurt performance and others really bring the beast out............but I have heard great things about this little .21, but i strongly suggest getting the XTM version as the warranty is easier to get.........for durability i get about 6-7 gallons out of my SH engines before i replace the piston/sleeve...but i am pretty abusive