Polecat - FYI , have a look at the work already done by CPI making cylinders for the TRX250R ( based on CR250 ).
http://www.cpindinc.com/pub/view_pro...6101-6872-1303
The smallest version has a 72 stroke with 68 bore - this would translate to a 1046cc 4 cylinder.
What they call a long rod is 130mm , but thats bullshit. If you use a CR500 rod at 144 that puts a very different light on things , with a 72mm stroke.
It is alot more beneficial to add stroke than it is to add bore in this case as it is much easyer to construct better duct geometry , plus getting sufficient Blowdown STA ( in a full house tune situation ) with undersquare , is much
easyer than going away from the idealogically correct square bore/stroke - with a bigger overbore.
The only downside is piston speed , but at this time all the MX engines at 250cc use 72 stroke and have proven to be race reliable at 10,000 rpm all day , in kart roadrace scenarios.
The other thing that is a bit of a hobby horse of mine at the moment is to optimize the cooling circuit , especially if it can be done at the design stage..
All the cold water should ( after cooling the case ) enter the cylinder each side of the boost port - travel across the transfers , cool the Ex duct area , then go up into the head.
If this isnt possible , then a single entry above the boost port , directly into the water jacket has the same effect.
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