What Bore should I go, Dont want any problems

[gtx400ex]

I have got a 05 400ex. The motor is starting to feel a little weak but not blowing oil yet. Wanting more power also but dont want problems withover heating or top in problems. What do you all Suggest. Also is the timing key worth buying. Any ideas for more performance?

[UnderFire]

you'llhave a less reliable bike no matter what bore, but if you are set on it, go 416.

[gtx400ex]

Anything else you would suggest

[UnderFire]

Originally posted by gtx400ex
Anything else you would suggest
seems like the 440 kits have issues with cooling, and a 426 bore leaves the head a little thin.

you could also just have it honed, it would be like a 1 or 2 cc bore, and it would still be more reliable.

[gtx400ex]

Know anything about a 406?

[UnderFire]

Originally posted by gtx400ex
Know anything about a 406?
not really, seems like it would be just a small hop-up.

[brian76708]

I think the 416 would be the best for max power for minimal decrease in reliability if your that worried about it go with a 406 but what makes most of the power from rebuilding it is adding higher compression piston and cam.

[jcs003]

JE 435 kit. 12.5:1 compression

[Punkmaster Flex]

He asked for reliability. ;)

I'd go with a JE 416 10.8:1. The compression will barely be higher than stock while adding a bit more displacement to your quad.

Either this or a JE 430 10.8:1 which will still have the low compression, reliability and a new sleeve so no worry about a thin sleeve like on a 426. :)

[honda400ex2003]

i would go with a nice 416 with a stage 1 or 2 hotcam and a nice port and polish. match that with a good exhaust and you will be very happy for a long time. get a hd cam chain such as a crf 450 chain and maybe cam chain guides along with a tensioner if yours is wore out. Grind out the welds on your stock header and get a nice slip on to go with your power curve and you will be set. if you like more mid and top get a stage 2 and if you like more low get the stage 1 you will not be dissappointed. i would go 11:1 je or wiseco with the 87mm to get the 416. Get a good set of cometic gaskets or something along the lines and you will not have problems with headgaskets or heat. dont let it idle for 20 minutes and shut it off when idling. get some scoops and you will be set. steve

your not really gains that much power from overboring its more of compression choice and other things. IMO if its tired or you want it fresh go 10:1 Wiseco 406cc, stage 1 hotcam, 6 degree timing advance, do all the free mods you can, hopefully you already have a good exhaust and intake then tune it right. It will move for sure and be reliable. A lot go 11:1 but i'm convinced a 10:1 and a 6 degree ignition advance will pull harder and be faster than a 11:1 and i;m probally going to get bashed some how for this but an engine isnt all compression for power, timing plays a huge role too because its something that will actully change the flame front speed.

[n811]

I have a 406 (I like to call it a 408)with 11:1 and I can run right with most 416's so I saved the bore for when this head is toast!

[honda729]

I had a 12.5:1 416 je stage 2 cam and HD studs for about a year with no problems, my friend has a 11:1 406 with a stage 1 cam and a good port and polish, he's had it for about a year and a half with no problems. The 406 will stay with my 416 untill the top end.

[416exman21]

go with 416 and get somebody to do your heads like trinity or ducan--- 406 would be kinda waste of time and money - my 416 walks 450's all day - just do it right ---good luck-