To big bore or not to big bore?

Blue_SV650S · World Chat Champion Joined: 27 Nov 2008 Karma :

Been thinking about getting a big bore for my WR250F.

After some googling on the subject, there is mix reports of big-bore kits, ranging from horror stories of big ends saying 'no' very soon after fitting to 'absolutely no problems'. Seems the main choices are Athena 290, Vertex 300. (no point going for smaller ones).

The obvious alternative is to get a WR450F, but I am not sure what weight/weight distribution penalties there are with that, the 250F has a marvelous chassis and weight dist, it is just the motor/gearbox that lets it down (IMHO).

I can see that the big-bore might solve/reduce the amount of gear changes required on the 250, but it WON'T solve the gear ratio problems (1st is too tall, 5th is too short).

Your thoughts on big-bores? ... and is the 450 just as silly ratio box as the 250 {saunters off to look up ratios}
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The purpose of life is to fight maturity.

G · The Voice of Reason Joined: 02 Feb 2002 Karma :

Heard good stuff about big bore 250 4 strokes for trail riding as well enduros.

Blue_SV650S · World Chat Champion Joined: 27 Nov 2008 Karma :

450F .................. 250F
Gear Ratio 1st
2.417 (29/12) 2.385 (31/13)
2nd
1.733 (26/15) 1.750 (28/16)
3rd
1.313 (21/16) 1.333 (28/21)
4th
1.050 (21/20) 1.042 (25/24)
5th
0.840 (21/25) 0.815 (22/27)
Primary Reduction Ratio
2.818 (62/22) 3.353 (57/17)
Secondary Reduction Ratio
3.571(50/14) 4.000 (52/13)

Thinking

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The purpose of life is to fight maturity.