Just thought you guys might want to know this but the bore & stroke on the quad is 95mm X 62mm giving it 439cc's & the dirtbike is 95mm X 63.4mm giving it 449cc's....so there might be a little more lost horsepower from the bike engine than we 1st realized.

 

Yeah it says 439 on the site. I wonder why they rounded it to 450.[img]i/expressions/face-icon-small-confused.gif[/img]

 

Don't you think they should call it a 440?? Oh, well it will still open up a can of kick a$$....... I KNOW IT!!!

 

I guess it's just a marketing thing. That YFZ will be an awesome quad for sure, & I applaud Yamaha for coming out with it. Guess I better put my 02 Banshee in the trader soon........

 

its so that you can race it right now the limit is 440....

 

Yeah...usually a shorter stroke motor will rev quicker that a longer stroke motor, so it might even be an advantage in a way. Ahhh who cares!!!!!!! I WANT ONE!!!!!!!!!!!!!!!

 

the thing is sweet! i want one! now just to find one?

 

i think they just put a shorter stroke to allow the quad with his overweight comparing to a dirtbike to get quicker response out of it,
it is a good move...

 

One question: This engine started life as a 400, then a 426, then a 450. When you need a rebuild, is there anything left to bore out for that new piston??? Or, did they take all that extra metal at the factory??

 

The YZ450 motor isn't the same motor as the old 400/426. It actualy shares more parts with the YZ250F motor!