I've had all the bore sizes on my 400EX….everyone will have a different opinion, All I can say is that I now have a 406EX and it'll do what the 416, 428 and 440 would do. I recommend a higher compression piston over big bore any day on the 400EX, take the money saved and do a port job. Also a longer swing arm and revolved rear shock will help a lot, couldn't live without a Lonestar +1.25" swinger anymore…..If I started all over that longer swinger and suspension would of been priority one over the engine. Most send the stock 450r shocks out….but being your weight play around with, you can adjust preload on the springs and compression settings….you may like them like they are. I run 11:1 compression, slightly higher cause a had the head plained a little, the 440 is reliable until you go higher compression then you have to watch things….like a 12.5:1……I needed GT thunder head studs to stop blowing gaskets.
1984 Honda 200M ATC
1985 Honda 200X ATC
1986 Honda 200X ATC
1999 Honda 406EX....11:1, Web Cam / Hardened rockers. Ported. WB CDI. CT Racing header. WB E-Series slip on. Lonestar swinger.
2001 Honda/KTM 520 Hybrid Quad. Its like a 400EX but twice the horsepower.
2014 Artic Cat Wildcat Trail XT