damn your freakin lucky!! i Want a klx450r!!!!!

 

Save the headache, get a brake light and whatever else one needs in one's state on the KDX to make it street legal. Baja Designs does a kit. Way easier and less costly than doing an engine swap and having to figure out where to stick the expansion chamber.

As for trying to stick an MX motor in the frame, why bother? The MX suspension is better and the general bike is lighter. Again, dual sport kit! I had a friend who built a supermoto CR500R. Bad part is the gas mileage is so bad with the stock 2 gallon tank he couldn't ride it all the way to work about 40 miles away.

You want faster, buy a big bore KTM dual sport.

 

these things sound like the most logical thing to do lol

 

 

I'd bolt the lights from the KLX250 on the KX450 and get the necessary electrics to run them, even if it was total loss battery and license it. Far less work for a better frame/suspension/engine bike. Better yet, I'd look for a used KLX450, if one can be found, CRF450X, or Yamaha WR450 to do it since they already have wiring for lighting and only need a brake light.. If I had a lot of money I'd go buy a new CRF450L and remove the restriction limiting it.

Just saying trying to wedge a 450 in that frame is an exercise in futility for a lesser performing motorcycle than can be done using the complete 450 - or the CRF250X or WR250F enduro bikes for that matter.

 

Regarding the KDX lump in the KLX frame, I think the exhaust port is in the wrong place on the KDX engine expansion chamber would run right into the frame.
These discussions are of interest to us up here in BC, Canada as all of the loopholes that allowed plating of offroad bikes were close several years ago.

 

You could try a probably totally illegal, but probably hard to detect by the unknowing - Get a KX450 and a junk KLX650 frame with title. Weld up the numbers on the KX frame, stamp in the numbers from the KLX650 title, maybe put on the metal year plate from the 650 frame, then take a torch and burn out the frame numbers on the KLX650 frame.
This could possibly be done with a 250, but the 650 would be more convincing. Could say you put the 450 engine into the frame.

It has the numbers, the title and all. With the 650 frame destroyed in the area of the numbers there is nothing there anymore. This is really the same as someone putting a new chassis and engine into a 55 Chevy. You know few of them could ever pass a pollution check. All they have is a title for the sheet metal. One consideration would be to get some KLX650 stickers on the bike to continue the charade.

This might be an area for someone to check up on the stuff for custom car building.