Best bore Size for a 400

[N400Ex]

I know I know... i already did a search...nothin. I just got the news from my mechanic that i hafta bore my quad out. 416, 426, or 440? I want somethin with alot of power but tat the same time i want a reliable size that wont break all the time. Also... I really dont wanna run VP fuel in it after it gets bore cause thats a ton of money... but is it a must? Thanks-

[2004exrider]

Im gonna have to say 416 with an 11:1 compression ratio. This will be cheaper, easier to build and very reliable and youll still be able to run 93 octane.

Jimmy

[Honda TRX250ex]

what octane do you have to run with a 426?

[400-416EX]

I would say 416. It will pull hard and be very reliable. 426 should still run on 93 if you go 11.1 compression

[N400Ex]

alrite so either a 416 or a 426... the other thing is.. does wiseco make that size? cause thats the company i think im goin with...

[fitethesystom]

416 forsure they make, above that I don't know

Try to stay away from the large bores if you want reliability and longetivity.

[2004exrider]

Yes, wiseco makes those size pistons. But since they base their compression ratios off the xr400 engine then say a 11:1 for the 400ex is gonna be a 10.8:1. But if you put the XR head gasket and base gasket on your ex you'll now have a true 11:1 compression ratio. The only reason it changes is because the EX engine has a thicker head gasket than the XR.

Jimmy

[JOEX]

Bore it only as much as you have to to get the cylinder in shape or to match up to the next common sized piston. As far as being reliable it depends on how well it is rebuilt and maintained.

Compression ratio determines what octane fuel is needed not bore size.

440 would definitly be the most powerful

[98warriorboy]

440 hands down, my buddy has a 440 on his 400 and it is bad as hell. definently go with the 440! u wont regret it!

[DAVE14]

go big or go home my 440 has been great, reliable & no different than stock except for alot more power get an 11to 1 (change the head studs) piston/sleeve kit & it will be much healthier than stock while being safe enough to run the stock rod & while youre in there ya might as well drop a cam on top to get all the power you can (I run a 12.5 to1 & Im gonna stroke it anyway for even more power) but its totally reliable & totally spanks a well modded ex no problems at all dont beleive the b.s. about problems or unreliability if its done right no matter what the bore size it will be much better than stock !