ok so i bought a 2007 400ex last year when i first got it it had just an after market pipe and plenty of power for me i moved up from a 86 lt 230 sport quad. now that i am use to the power of the quad i wanna start putting some more power into it so i bought a k&n power air box lid and lookinginto an after market air filter. also going to buy a amr stage three CDI and amr monster coil
i have done some research on big bores the last few days and i have found that to make a 440 kit worth the time you gotta get an aftermarket header and port & polish and put a lot of work into it to make it reliable. and that an extra 600+ bones i don't have at the moment. so that leaves me between a 416 or a 426 i haven't found much info on the 426 i just wanna know what you guys think.

my questions

with a 426 would i need to port ?
what's would be the best compresion?
what are good brands of pistons to buy je or wiseco ?
what stage of hot cam would be the best?

thanks for your time and hopefully you can help me out

 

Go for a 460 stroker all the way. My brother in law did it and it was insane. I had two people on it and it would acclerate like there was no one on the quad. He had some head work done and re-cammed it but after the money was spent, it was a killer quad!!!

I have a 440 kit on mine and im thinkin about goin to the 460 just for poops and grins

 

and then go to gt thunder to get some aftermarket head bolts because you going to strip them due to the excess heat caused by your big bore engine...and then go get an aftermarket oil cooler or at least an aftermarket(read way bigger) oil resevoir so you dont find yourself riding around on a molten lava powered quad.

 

I have a 2001 Honda 400ex and I just bought a 11:1 hi compression ( 416 big bore kit ) I was wondering if I would be able to run 91 octane pump gas with that on a stock head

 

With proper jetting most dont need to use race gas.

 

just buy the 440 big bore kit & hot cam (2)- rejet like jgar said or buy an edlebrock carb like i did. regular gas is fine.
any shop will machine the jug for not too much $$ and the rest you can do.

you'll have all the power you need.

 

depending on the compression ratio it is fine to run regular gas,over 11:1 you need to run race gas or a 50/50 mix,if you do get the 440 kit make sure you get gt thunder head studs,the best carb for a modified 400ex motor is the 04 450r carb or the fcr carb,you will also want a bigger oil tank to help keep the motors temps down,and you will also want the stronger crf450 cam chain that's tougher because if you put the 440 kit in it the stock cam chain will be stretched in no time

 

My question is I have a 400ex with every mod you could think of,it has a trx450r carb on it,has anyone tried to put one of those air fuel mixture screws on this carb,when I went to purchase one its says for fcr carbs only.I need this because of its easy access,Also when I do turn the air fuel screw out to 2 turns it seems like its loading up at idel and then back down,it works great when adjusted about 1.5 turns out.anyone has any ideas,it would be greatly appreciated.thanks