the 300ex has 4 valves, i had the head off last weekend and there are 4 tiny valves. also my 83 xr500r has 4 pretty decent sized ones too.

 

go to google and type in 400ex big bore. then find the atv illistrated one and it shows a pic of it

 

300ex and 400ex are 4-valves. and the raptor has 5 valves. the YFZ has 5 valves.. the KFX/Z/400 have 4 valves... all the "Top class" Performance machines have 4 valves, apposed to say a Raptor350/warrior wich has 2 valves.