the 2 .18's out there are the fantom and sirio that are direct fit. Both will work with the easy or pull start from the 2.5. They do require a different header then what is supplied and on my rustler with the fantom you can not access your lsn because the transmission blocks access to it. I haven't found this to be a problem though. The only problem with these engines is keeping your transmission in one piece. There seem to be no upgrades for the planetary gears and cups and these are what I have been grinding through. I cleaned and fixed everything and gave them a nice coat of molybdenum grease and adjusted the slipper very carefully and I seem to be fine now. It is an extremely fast engine and all you'll ever need in the rusty.