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250xcfw BIG BORE 280 VS 300

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Hi,

I'm thinking of doing a big bore to my 08 250XCFW. Not sure which way to go. KTM SXS 280 is one option. Can get it for about $630 from Munn Racing and you get to keep your origanal cylinder. Thumper Racing 300 is a rebore cast liner. If you send them your cylinder it's about the same price. Any input pro and cons. I had a 290 Athena kit in my 03 WR250F and loved it. And miss it.

Thanks.

Edited by acormier7

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The 280 kit on the 12 (similar engine I believe) adds 3 hp all the way up , it makes 21lb ft of torque and is easily the biggest bang for the money

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I have a TR kit on mine. Sent it to them for liner change. Is a good kit, lots of low end added. They also give jetting specs.

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Yes I think there was a problem with the overheating , not sure what the differences are with the kits

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I have a TR kit on mine. Sent it to them for liner change. Is a good kit, lots of low end added. They also give jetting specs.

Did you do any other work? Head work, cams, pipe? I'm leaning towards the TR kit. The only draw back to the TR kit is down time.I can do most of the work myself except the honing. I work in a machine shop but we don't have a good honing machine.

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A friend used the KTM kit and really likes it. Have also heard great things about Thumper and their service.

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Hard Parts kit is 280cc whereas Thumper's is 290cc which means your getting an extra 1/3 over the Hard Parts

People who've had both say the Hard Parts likes more rev and Thumper has more bottom

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I love big bore kits and have a 280 kit in mine right now, but they are not all created equal.  This notion that it's going to run just like your stock motor but with 3-4 more hp is not necessarily true.  It's not rocket science, the pistons in some of these kits are very heavy.  I took 8 grams off of mine and it runs so much better now.  Mine came with my bike but if I were to buy one I'd look into using a CP piston and have your cylinder bored and replated.  CP pistons IMO are high performance pistons and of the several that I've had (stock bore) are lighter than stock.  They add weight to the pin to compensate. 

 

http://www.campbellenterprises.com/ktm/pistons/ktm-250sxf-cp-pistons-high-compression-big-bore-kits.htm

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Isn't some of the cylinders too thin however so a new casting is needed

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Isn't some of the cylinders too thin however so a new casting is needed

 

Sure... the CP big bore in the link above is 3mm bigger (270cc).  I imagine that is the largest overbore you can safely go with the stock cylinder.  I am not sure what the big bore and plating costs but it should come in below or around what the kits cost ($550-$600?).  Assuming that the CP piston is designed to be light unlike some of the kit pistons, the 270 should out perform at least the 280 kit on a moto track.  All speculation though!

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I have 5 years on my atheena 290 yzf kit, one point to consider is that atheena has bigger coolant passages in the cylinder to provide better cooling than a stock cylinder.

my bike has never boiled over spiting coolant in the tight trails but my friends stock ones all have

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I have 5 years on my atheena 290 yzf kit, one point to consider is that atheena has bigger coolant passages in the cylinder to provide better cooling than a stock cylinder.

my bike has never boiled over spiting coolant in the tight trails but my friends stock ones all have

Thumper Racing has addressed this with fins on the outside of the cylinder liner.

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