Old Question, new answers?

5 replies to this topic
  • YZR426

Posted March 08, 2002 - 03:29 AM


I want to change from the original '01 426cc to a 450cc big bore kit eng. Has anybody played with this size and what did you find, reliability, quik rpm's or slower , torque range ? (if so what manufacturer)

Has anybody used race cams and larger valves with the big bore kit as well.

What about ceramic coating of the internals (pistons and valves?)

Thanks in advance for your replies.

BTW you've probably guessed that I'm chasing some more serious HP :)

  • bullitboy

Posted March 08, 2002 - 04:08 AM


Do a search on the 444 upgrade and you will get some info there.

  • Jon_Escombe

Posted March 08, 2002 - 11:39 AM


I went 3mm oversize which works out to 453cc.

The stock bike was making 45hp, the big bore brought it up to just under 50hp. Gas flow, big valves, and cam timing has got me to 52.5

It makes more power than stock everywhere, but flattens out between 7k & 10k rpm. The oversize inlet valves made a couple of hp through the mid-range.

Reliability hasn't been a problem so far, but I'm being pretty anal about rod changes (20 hours max). I'm looking at high-lift cams to help it breath above 7k..

Cheers, JonE.

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  • YZR426

Posted March 10, 2002 - 02:42 AM


Thanks for the info.

I will give it a go.

  • gal

Posted March 10, 2002 - 04:55 AM


im jelous of u guys that u need more power then the stock yz426f n i hope u will use it....

  • Jon_Escombe

Posted March 10, 2002 - 06:56 AM


LOL! My YZF is a Supermoto(SuperTT) machine. Haven't braved a MX race on it since it was stock - I'm quicker in the dirt on my YZ125!! :)

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