Piston, cam, bigbore for 400?

5 replies to this topic
  • bluebreadtruck

Posted October 22, 2008 - 05:21 PM


I have my wr timed to yz specs and love the top end power, however i would love to get some more mid/low power without loosing the top.

With my old 4 strokes, i would always add a highcompression piston and a cam, and maby bore it.

My question is with the 400, what is stock compression, and can i run a higher compression piston with pump gas?

would an aftermarkert cam set like a hotcam, etc really make a difference in power?

Do they make a big bore for an older 400 like mine?Is it possible to swap in a newer 450 cyl? thanks alot guys....been riding the bike stock and love it, but always looking for more power....ive been riding with streetbikes lol.

  • tcmII

Posted October 23, 2008 - 04:02 PM


check out this link. They offer a 400 to 426 with a bore change or 400 to 440 option with a bore and stroke change.

I was looking into this and didn't finish the research. I was thinking that if you only wanted to go to 426 you could buy a 426 jug and and a proper oversize piston for the 400, you might be able to do this without the crank/rod change. Maybe some else knows if the piston is availabe. This could save some cash.


  • bluebreadtruck

Posted October 23, 2008 - 05:17 PM


thanks. could you use a 450 jug, piston and crank in a 400?

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  • Oasis_Flame

Posted October 24, 2008 - 01:08 PM


Yes you can because I've done it 4yrs and 5000 miles ago. Wiseco carries the piston 13.5 to 1. Stock is 12.5 to 1. I'm using a stock 400 head, crank and carb. Runs on pump gas all day long and man is it tons more powerful. I bought a stock WR 426 jug off of E-bay for $50.00 in great shape no boring needed. Jetting was nothing to figure out.

  • bluebreadtruck

Posted October 26, 2008 - 04:57 AM


oh, so wiseco makes a 400 piston that will fit in the 426 bore sleeve? im a wiseco dealer so yay!

  • bluebreadtruck

Posted October 26, 2008 - 05:08 AM


OK, i just checked out my wiseco catalog

I see they make a 13.5:1 400 piston and 426 piston.

Could I buy a 426 or 450 jug(same 95mm bore), buy the correct piston and bolt it up?

Do all years use the same wrist pin size? I heard there is a cutoff year, but wanted to verify.

can you run 13.5:1 on premium?


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