400 to 426 conversion

3 replies to this topic
  • deerhunter

Posted April 11, 2004 - 07:57 PM


My 00 wr400 is due for a piston and I am considering going to the 426 displacement. Has anyone had any reliability issues, is it worth the money.

It already has all the free mods, FMF PC4 exhaust, YZ timing, BK mod, JD jet kit. The bike rips right now and has plenty of power but who doesn't want more. :)

  • Matt96xr6

Posted April 12, 2004 - 06:02 AM


Talk to Wiseco directly. A friend is rebuilding his 400 and Wiseco suggested to go to their 417 kit. It makes more power than the 426 conversion because the compression is lowered using the 426 size bore. The 417 actually bumps it up a point.

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  • Oasis_Flame

Posted April 12, 2004 - 10:32 AM


Use the made for WR rod Wiseco 13.5 to 1 comp. piston in a 426 barrel and you will spank the 450's. Not to mention CR 500's, useing pump gas and YZ exhaust. I did the conversion 2 yrs. ago and now have 2000 miles on the motor with zero problems. :)

  • MrBlahh

Posted April 12, 2004 - 12:07 PM


I've got the same setup, 444cc's at 13:1 makes too much power for me


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