another +1 on the 2072 pipe here for the .25 6port. I'm not a fan of the 2072 pipe for .21 motors but on the .25, its perfect. I didn't worry about the extra shim for break in, just run it in nice and your giggling. I put a 14T bell on my losi when I had the .25 as it has so so much torque down low and the 14T made it scream in the top end and made for mind boggling top speed. Where I only dropped a couple of teeth on the spur when running a .21. Have fun with that, also found the turbo head button allowed it to rev a bit better up top.