I am not up on all the after market motor stuff so I have a couple of ?'s about big bores vs strokers.
First and foremost what do you get with a big bore and what do you get with a stroker, I mean what is the difference in parts and/or installation?

Second if I were to make my 400EX a more powerful/faster machine which is the way to go? I thought about buying a bigger bike but love my 400 to much and would like to surprise some of the big bore guys with a little 400. Right now I have an LRD slip on, K&N filter, rejet and a modified airbox. How much gain would I get from either of these?

What is the install time and difficulty level for each?

Thanks in advanced for answering my possibly newbie type question.

 

Boring a quad is not a huge noticible difference in performance, espessially in a 1 piston quad.

If you bore, port and polish and shave the head on the quad you can get a noticable amount of power out of it. It will raise your compession and give you a slight advantage. This involves removing the jug from around the piston and putting a new piston in. The shop does the rest of the work.

As for the stroker this is where you get into some power. Installing a stroker kit will be a 10 for difficulty, drop the motor and tear it down to the crank. With a stroker you will need a kit which will run you about a grand or so. I would also mill the head with the stroker kit.

What I would do, is if your gunna do work on the motor and like the quad that much. Do them both. A 440 stroker ex with a shaved head and 94 oct gas will hold its own against any 450.

You may want to consider a bigger carb if you are going to go either route.

 

One of my riding buddies has a 13:1 440 kit in his 400 ex and it would walk away from my 450R when it was stock

 

Now that I have my cam, exhaust and 480 kit, he don't stand a chance.