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Would the hybrid build be good on the track? If so what frame, pipe, an suspension should I use. I have a tight budget, and weigh 185 pounds.

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-Matt

Valving for MX is a good bit different than trail riding. The KDX engine won't be as good as a MX engine when used on a MX track. Most beginner and novice class races are won by the rider, not the bike. Getting to the first turn is another story. Most 250 two-stroke MX engines in the past ten years put out 45 or so HP. You better maintain momentum!

250 mxer's have been pulling 50hp since the 90's, some pushing upper 40's in the late 80's. The KDX has been tuned (Plugged if you will) for trail riding purpose. If one were to clean the porting up, up the compression, and throw a 38mm PWK while utilizing a kx125 air boot I think it could pull an easy 35hp+ no problem. It would be putting out the same hp as a 125 but with more torque(2012 ktm125sx is putting out 39hp). It would be dope, but what is the point? If the AMA allows a 250cc 2t against 250 4t's in the amature class, this would sort of an odd duckling.

You can't beat a motocross bike for motocross but if it's local club racing, and you're just in it for fun, it sounds like a good time to me. Not everyone likes a full race bike, or peaky powerband.

If you do a hybrid build with an early to mid 2000's KX125 frame you'll have a good track bike. I don't think it would end up being "faster" than the KX125 it was made out of, it would really come down to the rider.
If you want to make your KDX better on the track a set of KX forks would have the most benefit, IMO.

factoryX wrote:250 mxer's have been pulling 50hp since the 90's, some pushing upper 40's in the late 80's. The KDX has been tuned (Plugged if you will) for trail riding purpose. If one were to clean the porting up, up the compression, and throw a 38mm PWK while utilizing a kx125 air boot I think it could pull an easy 35hp+ no problem. It would be putting out the same hp as a 125 but with more torque(2012 ktm125sx is putting out 39hp). It would be dope, but what is the point? If the AMA allows a 250cc 2t against 250 4t's in the amature class, this would sort of an odd duckling.

According to the Kaw factory E bike manual, the KDX200 puts out 35hp at 7500rpm. Not sure how much this is fudged....

This is also most certainly FWHP, although I'm sure the KTM's published figures are FWHP as well.

At the sprocket yes, but at the wheel its in the mid twenties. Apparently is can easily be made to hit mid thirties.
http://justkdx.dirtrider.net/dynotesting.html

Interesting to see similar results from the KTM. Kind warps my brain as to why I had to have the yz250(total face palm)

A stock 250 two-troke MX bike doesn't put out 50 horsepower ( though the 2012 KTM comes close).

A stock KDX is around 28.

The dyno chart is for:

"His engine has been modified using FRP porting, head work, a Boyesen RAD valve, FMF pipe and silencer as well as a modifed carb."

$900-ish to get there.

Anyway, for local MX racing, you will have fun. Don't take it too seriously, and you won't have to run out and buy a MX bike to try again.

Those dyno charts made my day!!

Get out on the track and give it a try. It would be great fun!

Jason wrote:A stock 250 two-troke MX bike doesn't put out 50 horsepower ( though the 2012 KTM comes close).

A stock KDX is around 28.

The dyno chart is for:

"His engine has been modified using FRP porting, head work, a Boyesen RAD valve, FMF pipe and silencer as well as a modifed carb."

$900-ish to get there.

Anyway, for local MX racing, you will have fun. Don't take it too seriously, and you won't have to run out and buy a MX bike to try again.

The 2012 ktm250sx dynos right at 50hp, and that's with a 36mm pwk...

I've seen a KDX motor dyno over 50, but you wouldn't want to use it on a bike again ;)

O.o

Can't wait to kick some ass on my 15 year old bike next month!