Used to race 250R about 15 years ago - Thinking of getting back on the race track - most likely my 15 y/o son will be the pilot

I can get a pretty much stock 2005 450R (piped/jetted) or one with porting/cam/etc work for within $1000 of each other.

I need advice on which one to pursue. The main concerns are with a stock motor, will mods be needed to make it competitive ($$$) and with a modded motor, will they need more frequent rebuilds and/or the added expense of race gas. (again $$$$)

Thanks for any/all advice.

I would get the stock then add your own mods for not the $1000. THen you know what exactly has been done to it. A Performance Clutch, New Piston and New Silencer go a long way and you can get all that for under $1000. Plus then you don't have to do race gas etc.

I agree. In addition, suspension upgrades are one of the easiest ways to gain speed, more so than motor work usually. A good pipe and intake should give him enough power to get started with.