426EX,

First, I had to ask, How does a a freshly raped ape run?

Second, good lord son, How do you know how a raped ape runs?

P.S. what is the top speed of a raped ape.

Just wandered...........

 

So with a wild cam profile, you might have a better chance of running pump gas with an 11:1 piston? With the stock cam, you would almost definitely have to run race gas with the 11:1 piston?

 

from the factory, there is a difference. the center gasket is much thinner on the xr400 headgasket, this is how it is 1.5 points higher. the aftermarket probably just uses a xr400 style and runs with it, maybe that is how they sell the piston as higher compression by swapping gaskets. I put a xr400 gasket on mine and it made a difference.

 

Air hit it.Good to see another wrench in here who knows the bolts.Just to give you guys a better idea look at the yz426.It has pretty agressive cam,12.25 comp piston and it only needs 91 octane.My bud just got a new 00 yz426 and runs premium 92 in it with no probs.This Is Calif gas also,very loaded with crap.remember higher octane rating means gas burns slower to prevent detonation.Only run as high as you need so it doesn't ping,anything higher is useless and actually will hinder performance due to incomplete burn.

 

Actually the 400EX is 9:1 Stock
The XR400 is 9.3:1 Stock......