KX250F swap to 450 engine

motoman998
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motoman998
If you needed a dumb question on a monday morning, look no further than this haha.

With BRC doing their big bore on KTM250SX bottom ends, how hard would it be to either 1) put a 450 top end onto the 250 bottom end, or 2) swap engines completely if anyone knows how engine mounts, intake, all that would line up
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kb228
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kb228 4/6/2020 10:07am
4/6/2020 10:07am
Youd have to swap the entire motor. Ive got a kx450 and kx250 fully apart and theres just no feasible way to put a 450 top end on a 250 bottom.
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motoman998
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motoman998 4/6/2020 10:12am
4/6/2020 10:12am
kb228 wrote:
Youd have to swap the entire motor. Ive got a kx450 and kx250 fully apart and theres just no feasible way to put a 450 top...
Youd have to swap the entire motor. Ive got a kx450 and kx250 fully apart and theres just no feasible way to put a 450 top end on a 250 bottom.
From what you can see, do engine mounts come close to being similar? or intake and exhaust locations? or is this a lost cause that could only be dreamed about without completely cutting and welding frame parts?
kb228
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kb228 4/6/2020 2:12pm
4/6/2020 2:12pm
kb228 wrote:
Youd have to swap the entire motor. Ive got a kx450 and kx250 fully apart and theres just no feasible way to put a 450 top...
Youd have to swap the entire motor. Ive got a kx450 and kx250 fully apart and theres just no feasible way to put a 450 top end on a 250 bottom.
motoman998 wrote:
From what you can see, do engine mounts come close to being similar? or intake and exhaust locations? or is this a lost cause that could...
From what you can see, do engine mounts come close to being similar? or intake and exhaust locations? or is this a lost cause that could only be dreamed about without completely cutting and welding frame parts?
No theyre not close. Need cut and rewelded
mxracer666
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mxracer666 4/6/2020 3:50pm
4/6/2020 3:50pm
What would you possibly gain in this swap? They're both 4 strokes. You can get a 2020 KX450 at places for $6995, in it's purpose-built chassis. The plastics/appearance is the same. Why re-invent the wheel?
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motoman998
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motoman998 4/6/2020 4:03pm
4/6/2020 4:03pm
mxracer666 wrote:
What would you possibly gain in this swap? They're both 4 strokes. You can get a 2020 KX450 at places for $6995, in it's purpose-built chassis...
What would you possibly gain in this swap? They're both 4 strokes. You can get a 2020 KX450 at places for $6995, in it's purpose-built chassis. The plastics/appearance is the same. Why re-invent the wheel?
I've got a 2012 kx250f in my garage now. I love the suspension set up I've got on it now, and the bike overall feels amazing. If it was as simple as swapping engines and maybe manufacturing new engine mounts, it may have been worth my time to invest in it. but if it's as much work as it seems to be after some helpful replies, it isn't worth that effort and wrecking the possibility of going back to a 250.
CarlinoJoeVideo
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CarlinoJoeVideo 4/6/2020 6:56pm
4/6/2020 6:56pm
There’s so many things that are different, the bike wouldn’t work correctly.
Ecu would need update.
Exhaust would be different.
Suspension would need revalving.

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