bore question

**shutupnshift04** · 01-22-2005, 04:43 PM

i am going to be building a complet mx 400ex and i was wonderign which bore size would be best for mx racing. i want the best motocross engine avalible and also who would be able to build me the best motor i was thinking sparks or tc cause i had tc do my yfz and liked his work. i heard many different opinions and would like to hear from u gus cause you would know best. please tell me which would be the best.

**shutupnshift04** · 01-23-2005, 10:14 AM

some one please respond i need help on making this decision please i dont no much abotu 400ex's i have a yfz this is for my younger brother

**EvilJester400EX** · 01-23-2005, 10:24 AM

416. Fast revving, more reliable. I would not recommend doing a 425, most of my friends that had them blew up. Who knows, maybe they didn't take good care of them, but if I was going to do anything I'd send it to Tom Carlson and tell him 416 with everything.

**shutupnshift04** · 01-23-2005, 03:18 PM

i heard the 416's were great for motocross to but howcome the 440 isnt better for motocross wouldnt it make make more power and wouldnt a 425 make more power to? i dunno im new to ex's

**400exrider707** · 01-23-2005, 03:25 PM

I hear a lot of people say that, but I think its cause most people dont properly build their 440's. It just doesnt make sense for a 416 to be faster than a 440. If you want ultimate reliability then do the smallest overbore possible and do a high compression piston to get the more power. If you do a cam and piston combo it will be a lot better than stock.

**shutupnshift04** · 01-23-2005, 03:40 PM

o ya and iwant something that is gonna hang with 450's on the track to so he can try and keep up lol

**NacsMXer** · 01-23-2005, 03:45 PM

Originally posted by shutupnshift04
o ya and iwant something that is gonna hang with 450's on the track to so he can try and keep up lol

All I can say to that is: GT Thunder 452 stroker kit!

**JDiablo** · 01-23-2005, 03:52 PM

alot of people go with the 416 because they rev so much damn faster then the other ones,i researched this,and i was going to go with a 460 LRD kit,but now im going with a JE 10.8 -1 compression piston,hotcams stage two,ported and polished head,lighten freewheel,fcr carb,and full HMF exhaust

**K_Fulk** · 01-23-2005, 05:43 PM

The 440's and 426 ive had seem to pull out of the corners a lot harder than the 416's ive rode.

**Blastermax** · 01-23-2005, 05:52 PM

I know someone with a 400ex and he hasnt had any trouble with it or anything..

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