yz450 into a 400

8 replies to this topic
  • hart92

Posted November 13, 2008 - 05:33 PM


has anybody turned there yz450 engine into a yz400 engine. i read an article a year or so ago about a company that sells a kit to do this, and the testers liked it from what i remember. was thinking when ,and if, my 06 is in need of a rebuild this might be nice? but i can't seem to find any information about it.any input appreciated,thanks

  • hondacrf250rrr

Posted November 13, 2008 - 05:36 PM


y would u want to down grade to a 400

  • love2strokes

Posted November 13, 2008 - 05:37 PM


it sounds like a neat idea especially for woods riders out there looking for more tractable power, if i had a yz450 I would definitely be interested in this mod

  • hart92

Posted November 13, 2008 - 06:18 PM


y would u want to down grade to a 400

i don't think it would be a down grade? i think a 400 four stroke is what the manufactures(yamaha,ktm) should have kept,or built(honda,kawasaki,suzuki) to begin with. i love my 450 on an outdoor mx track,but i also ride woods and it can be a handfull. i also owned back in the day a 99 yz400,and the bike barely compares to the new ones as far as handleing goes,but that engine was super sweet, and very manageable.

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  • Frank_z28

Posted November 14, 2008 - 05:59 AM


I saw that mod in a magazine. Ill try to find who doing the kit.

  • ncmountainman

Posted November 14, 2008 - 07:36 AM


I saw that mod in a magazine. Ill try to find who doing the kit.

L.A. Sleeve did it to a crf 450 awhile back,they may offer the same for the yami?

  • grayracer513

Posted November 14, 2008 - 07:59 AM


IMO, based on experience, the way to make the bike more useful as a woods bike would be to make the engine bigger, not smaller, then take the edge off of it with milder cam timing. Within the confines of the current engine's physical dimensions, this would be difficult on the scale I have in mind. I would stroke the engine all the way to 500cc, and increase the weight of the crank by at least 3 pounds.

That would require a 70mm stroke, however, and I doubt that's possible without a custom cylinder and a longer rod, if even then. But if coupled with cam and ignition timing on the order of an early WR450, it would produce an engine with a lot of very usable grunt at low speed, still capable of spanking it when necessary.

But, the conversion of a 450 to a 400 by reducing the bore 89mm would yield a similar bore stroke ratio, and it could be one way to go. It doesn't appeal much to me, though. There's no replacement for displacement.

  • thsp485

Posted November 15, 2008 - 02:28 PM


I read that test of the YZ 450 that was made into a 400. The testers all said that you could ride the bike faster and more agressively as a 400. It was supposedly easier to turn and less tiring, sorta like a punched-out 250F, only with more beans. It does seem odd to spend money to make your bike less-powerful, but it apparently works well.

  • hillclimbguy

Posted November 15, 2008 - 07:21 PM


These all sound good. But I like the "there's no replacement for displacement"
I paid to have horse power, and the YZ450 has it and is dependable, too. IMO if you want something easier to ride then add FWW. If not, then twist and hang on.

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