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How would the power of a crf450r compare to a kdx220 also handling in gran prix races

No comparison, the CRF has way more power . If you can afford to keep it running.

The newer four stroke motors are amazing, as in they have even more low end than a KDX, and just keep pulling up to the redline. Your arms will become very strong from all the power. However they are heavy and hard to turn due to the increased rotating mass in the valve train (an object in motion will stay in that motion unless forced to turn). Certain CRF450R Models have a reputation for poor valve and head life. Check other forums before you buy.

If your grand prix course is mostly moto oriented, it would handle and ride fine. Moto bikes are typically set up stiff for off-road use. The stiff suspension and extra weight and power wear you down over a long race. Hence I race a KDX 200 rather than my WR450F and turn faster lap times in Harescrambles. You see very few new 4ts at HS races, people are moving back to 2ts unless they race moto also.

I look that up, but the races are like almost al moto and sand

The Crf I'm looking at is a 2002

I would be very wary when purchasing an older 4 stroke MX bike. Repairs can be very expensive in comparison to a two stroke.

What should I consider as a newer 4t or 2t?

The newest KX or YZ 250 you can find and afford should do the trick. The YZ is still being sold in the states, although it's nothing but BNG for the past several years. Maybe a KTM or Gas Gas 300 if it's legal in your series. If you can't tell, I'm not much of a 4t fan. If I needed one for a particular reason, I'd probably look for a WR450F.

I was looking at a new 2012 ktm 250 xc, do you know anything about them?

I was looking at a new 2012 ktm 250 xc

Fine bike. Anything new you can't go wrong.

Keep the KDX for when you just want to ride!

The 07 KX250 is a quirky handler. 03 and 04 KX250s have better power delivery and handle better in my opinion. From what I have read, the 05 KX isnt a bad bike. Kawasaki messed with steering head angles in 06 and screwed the bike up. The 07 frontend is unpredictable and never feels planted. I have an 03, 04 and a 07. The YZs are good bikes but have powervalve issues. The center powervalve can break its stop tabs off and drop into the piston. It happened on my old 01 but I caught it before it broke both tabs off. My 02 wasnt so lucky. Ive also read about it happening on quite a few bikes. Keep an eye on it and you should be ok.

What exactly are the problems with the crf

CRF - Reputation for vaves failing at low hours and ruining the piston, jug, and head. I know of some that have run a long time with no issue. For the cost of repair, it would be cheaper to buy another bike and sell the red boat anchor.

The yamaha 4ts have a reputation for being the most reliable. All high rpm 4ts have higher rebuild costs with more moving parts to replace than a 2t. Like a Nascar engine. Makes it hard to afford to race.