I run my Xray xt8 truggy. With the os .28 and it is awsome I use the standard flywheal and it works fine. With mugen fibers and 1.0 springs and the truck is ballistick. I also own the new sirio cl7b sti. Great motor very smooth and toque for .21 because of the long rod. The rb is a great engine to. But I will kepp my .28 I 10 plus with the motor and dont have to spend alot of money alumiun shoes. Also with the fibers the truck will clear what ever you throw it. are tripple is over 32 feet and most of the truggies with the .21 sometimes dont clear. I say add another 10 foot to pleanty of power. Also try rocco silver state setup on xray. truck was awsome tons of stearing everywere.