if you run an upgraded engine it will usually have a little more torque so you can get away with higher gearing and if your not going to go to the fok i would go to at least a 16/49 and maybe a little smaller on the spur but only a little if you gear down at all you will tear the crap out of the transmission i have the lrp spec3 .28 with a 16/54 gearing i do have the fok and updated driveline 17mm wheel hubs and the associated duel chamber pipe running 30% nitro i had to go to the fok about a week after i upgraded then i went to larger wheel hubs about 3 weeks later shortly after that i broke my rear drive shaft and it went like that until i just replaced every thing bigger is not always better before you go larger there are several things you can do pretty cheap to squeeze the most from the stock setup first off the slipper clutch is pretty weak if you fill all the holes in the spur gear with friction pegs it helps i highly recommend the fok it makes alot of difference get rid of the stock tires they are very heavy a set of traxxas talons on revo wheels fit right on look good and shave close to 15oz off you can get them online for around 60 for all anything is better than the stock ones if you want more speed go 16/49 shorten the space between the muffler and the header you can cut about 1/4 off the header and really raise the powerband you can even add a head shim all these things will get the speed up but will hurt torque and bottom end punch and some may be a little extreme if you want low end pretty much go the other way spread the pipe until you have about 1/2 gap in the silicone hose a 15/54 gearing does good for bottom end the engine only has one shim do not remove it the piston cannot handle the heat and extra compression i have tried 2 times just get a long glo plug and go get the truck as light as possible if you go for the 54 spur i recomend
http://www3.towerhobbies.com/cgi-bin...&I=LXKLB1&P=OW i hope this helps