How badly would the 450r (bone stock), dominate a 400ex with a big gun exhaust system and a K&N airfilter

 

It would get ugly quick. A piped 400ex can't even run with a stock Z400.

 

Bad!!!

 

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From my experience the Z/KFX/DVX quads are only 1-2 quad lengths faster stock to stock with an EX.

 

I don't know if this is helpful but my 03 400ex will beat a stock 450R in the dunes. I don't even have a bore kit. The 450 is nice but for less money I can have alot faster quad.

 

I would rather get the 450r and buy like the HRC kit then go get a 400ex and go shopping for a thousand upgrades just to beat a higher model. Not bashing anything, im just in love with the new 450r

 

It depends on where you ride. If I hit a technical spot on the trails, I'd much rather be on the 400EX than on a 450R.

 

True

 

I have both the 450r and 400ex and the 450r is as good a trail bike as the 400ex. Even in the highly technical stuff.
Go down a tooth on the front sprocket (13th) and it is an awesome trail bike. The kick start is not a problem. I have never had reverse so I don't miss it or rely on it.
My 400 is piped and jetted and my 450 blows it way. I let my son get a head start in sand drags and I catch him by 3rd gear.
The 400 is a great machine and the 450 is even better. You'll love it!