most competitive motor bore

[QuAdEr 317]

next season im racing and i wanna kno what bore i should get so that 450s aint smoking me in the straghts n what not....what kind?what size? what all to get? also its for mx

[400exrider707]

Drop in a CRF 450 motor

[QuAdEr 317]

Originally posted by 400exrider707
Drop in a CRF 450 motor

thought bout that but thats big bucks
1) buy motor around 2 grand or more
2) jb to do my frame to acept it - around 800
3) radiatior for it - ???????

i was thinking motor work lik a 440 or 460 would be about 1500

[JDiablo]

go with a 460 like me

[gotahemi2004]

i got a 04 with a 440 just installed with port work and cam, carb , pipe , intake , plastics done for bout 2100 bucks.. i just cant tell if it has mor epower than a 40 cuz i havea yfz im use to rideing and going backt he 400 feels weird.. they guy said it should run with a 450 without a doubt... i got another 30 min or so before the rings set so i cant get on yet lol ill let ya know how it does in caparision to a 450

[Colby@C&DRacing]

I would build a 426 it has alot of torgue and will rev really fast. If you are going to keep up with the new 450's you need torgue and a motor that spinns really fast.

[TC426EX]

Originally posted by Colby@C&DRacing
I would build a 426 it has alot of torgue and will rev really fast. If you are going to keep up with the new 450's you need torgue and a motor that spinns really fast.

I second that reccomendation...

[QuAdEr 317]

Originally posted by Colby@C&DRacing
I would build a 426 it has alot of torgue and will rev really fast. If you are going to keep up with the new 450's you need torgue and a motor that spinns really fast.

thanks colby..if u were doing the work what parts would you use?cam,piston,pipe,carb, and what not....also what would be mandatory lik would i need a carb or what thanks a lot

[ckasper18]

Go with the 426 kit way more reliable and only a couple horsepower difference.

[RedRacer44]

I have had my hands in on a few EX builds and we had the best luck with the 426 motor. They rev fast and make a lot of torque, very fast and easy to ride on the MX track. We had problems keeping 440s together for long periods of time and 416s are nice but not enough power output.

The 426 power is very smooth and pulls hard outta corners, mind you its not like a 450R but the power is there. The last 426EX we had would run with my 450R when it just had a pipe. Granted I would pull him in 3rd gear, but he was right there with me in most of the holeshots.

That 426 had a 13.5:1 piston (if I remember right), White Bros Race Cam, Sparks exhaust, K&N Filter, and 40MM FCR carb off a CRF bike. We never got it on a dyno but it had some serious power. With some head work, that thing woulda been crazy fast! Only problem we had was the quad would blow a head-gasket every now and then