I figured I would throw my hat into the ring after reading all negative on the stock BXRSLSDI5, as my modified version of it is possibly the fastest most powerful offroad .21 I have ever come across...This is the first engine I have seen where its so much faster then everything else that it can make a clean pass on our straightaway...It is nothing short of awesome.... has insane amounts of bottom punch end and then pulls like a freight train all the way to 42 000 RPM and somehow manages to get awesome mileage doing it.It is a fairly substantial amount of work to get these results that involves lowering the exhaust timing and raising the intake timing thus lowering the overall blowdown timing which gives the engine much better power and mileage..... Anyways I have been doing these engines for many years and this SLSDI5 is something special in its modified form...it is truly an awesome engine with crazy amounts of potential....