Big Bore YZ450f?

8 replies to this topic
  • tnat1

Posted January 29, 2009 - 06:31 AM


I was wondering if anyone knows anything about the Athena 485cc Big bore kits for the YZ450f 2006, Are they reliable, how much HP? Would i need a bigger carb?


Posted January 29, 2009 - 12:53 PM


u really need that much more power?

if thats a case i wold just say ktm505

  • erickdj

Posted January 29, 2009 - 03:55 PM


going by his avatar picture, he might want it for supermoto, so he might need the power for that. Or he might be a big boy that needs lots of power to haul him around. The best thing about a big bore yz vs. the ktm, is that you're not stuck with a ktm.:banana:

  • grayracer513

Posted January 29, 2009 - 04:09 PM


He might just like overall effect that displacement has on things.

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  • jonova

Posted January 30, 2009 - 09:59 AM


I don't recommend doing big bores unless you are a motarder. I have done them all to my previous bikes and found that the longevity of the motor goes down. Train a bit harder, dial in your suspension and ride more, you will get faster.

But if you do, go with thumper racing. They have great quality stuff.

  • cheeta

Posted February 16, 2009 - 09:19 PM


i got an 05 with an athena 478 kit, hot rods crank an TLR performance ported and polished my head for top end along with a valve job. the athena piston fit the yamaha crank but not the hot rods, had to get the piston machined down.

  • barry450

Posted February 16, 2009 - 11:13 PM


What way did you have to machine the crank piston?

A WR/YZ crank uses a 18mm wrist pin where a YFZ Quad crank uses a 20mm wrist pin. Is it possible the HR crank you got was for YFZ?

And I am unsure how a big bore would affect the reliability of an engine, I have never seen evidence of this. What I find is most do more at the same time, like cams/headwork etc and then rev it harder. I see no reason going up in capacity slightly would make anything less reliable.

I am currently building an 05 WR with YZ cams, big valve head, Athena 480, JE 13:1 piston, bored out carb. Will let you all know how it goes.

  • cheeta

Posted February 17, 2009 - 07:43 PM


the wrist pin fit fine, it was the part of the connecting rod that was hitting the underside of the piston. this had to be a machining mistake by hot rods and when i called them to tell them, they said that it was probably the piston. I told them that the piston fit on the stock connecting rod and they stuck 2 their story. the hot rods crank was supposed to be to factory specs, apparently not.

the thing i noticed most about the big bore was it improved my throttle response, but when u get into the revs the bike screams and i cant stop grinning. the head work is awesome. i did send my carb out with my head and TLR flowed them together and i havent had to touch the jetting, but florida is all pretty much the same elevation.

good luck with it, keep us posted. interested 2 know how she runs

  • camman

Posted February 20, 2009 - 12:29 PM


You must slightly increase the rod small end when using a bronze bushing. The Hot Rods will always clear the OE piston. The Athena crown thickness must be greater than OE. Never heard this problem with CP, Wiseco, or Vertex.

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