Higher compression piston in '00 426?

2 replies to this topic
  • DethWshBkr

Posted July 10, 2004 - 09:21 AM


As I'm sure some saw, my dad blew his tranny up in his '00 426 a few weeks ago.

It is in the process of a rebuild, and my uncle (who is doing the rebuild), was going to put a 13.5:1 high compression piston in the bike. (Stock 11:1.)

ANyone do something like this, and have any benefits or drawbacks? We'd heard something of more torque, but a significant reduction in the bikes ability to rev.


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  • SFO

Posted July 10, 2004 - 02:15 PM


The high compression piston works well and is a win win in the yz-f.
I ran pemex in mine with no pinging.
The YZ combustion chamber will tolerate added compression without detonation.
If you want to go for more mods while you are at it set the deck clearance @.035" and have a GOOD valve job done having the chamber bowls recut and the seat transitions reworked.

  • Hamish

Posted July 10, 2004 - 04:36 PM


We'd heard something of more torque, but a significant reduction in the bikes ability to rev.

In my opinion, true and false, in that order.
It should actually rev quicker, providing the engines effective compression isn't compromised. That generally only happens when the dome is that big that the valve flycuts have to go deep inside the pistion, causing partial shrouding of the valves at low lift. Generally with only 13.5:1 and the very flat chamber that the YZF has, this wont be an issue.
Just make sure the fuel you use is up to the task. The only drawback I can think of is that the engine won't 'lug' as well, but who wants to lug a MX bike anyway?

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