250cc into 330cc big bore

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#1
i have been looking into big bore kits for cr250r 03 and i can get one turns it into 330cc any problems with doing this? is it a wise move?
 
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#2
i have never seen a 330 kit for the 02 and up cr250.265-280 at the most.eric gorr or maxperformance. :ride:
 
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#3
keithcr250r, i have heard that this engine will out pull the CR500 on the top and kill any KTM300 for bottom end. http://www.madmanengineering.com/bigborekits.htm
You can also bore it out to a 350. I have riden a TRX250 with the 330 and it was simply amazing the power it makes (close to 80+HP). But i only tested it from some randome guy from the dunes so i dont Know about the reliability.
 
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#4
thanks for the helpful link it is an expensive mod. and it will reduce engine life but i think it will be some fun..might have overheating issues :) i will look into 350..might need bigger fuel tank?
 
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#5
keithcr250r, if anything you will need a smaller tank. Bigger engines creat a greater vacume with in terms draws in its own fule. So, this means you would need to go leaner on your jetting. Also, the kit comes with its own cylinder that was casted so it would not onerheat.
 

john stu

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#6
2 strokes for life said:
keithcr250r, i have heard that this engine will out pull the CR500 on the top and kill any KTM300 for bottom end. http://www.madmanengineering.com/bigborekits.htm
You can also bore it out to a 350. I have riden a TRX250 with the 330 and it was simply amazing the power it makes (close to 80+HP). But i only tested it from some randome guy from the dunes so i dont Know about the reliability.


close to 80 hp............. :coocoo:
 
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#8
2 strokes for life said:
keithcr250r, if anything you will need a smaller tank. Bigger engines creat a greater vacume with in terms draws in its own fule. So, this means you would need to go leaner on your jetting. Also, the kit comes with its own cylinder that was casted so it would not onerheat.
Bigger engine, better fuel economy? Tell that to my bike.... :coocoo:
 

dirt bike dave

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#9
In my experience with a big bore (KDX200 to KDX240), I did go leaner on the jets. But the engine consumed more fuel and my range was reduced from 70+ miles to 55 miles.

Bigger cc = engine sucks in harder = same size or smaller jets.

Maybe in a motor tuned for drag racing only, you will need larger jets to accomodate for the other mods.

On my KDX, the jetting was like 2% leaner but it would suck in 20% more air/fuel each intake stroke.

BTW, I'm not a fan of big bores, especially if you need to remove the power valve.

You will probably end up doing extensive tests and tuning to get the motor to run the way you want it to. Then you may find that you are stuck with huge gains in one area, at the expense of others (my old 240 would not rev out like a stock 200, but made great low end). Your usable rpm range may be much shorter, and even though the bike will be stronger in that range, it may be inferior overall. Basically, be prepared to throw lots of money at it to get it to work they way you want it to. Custom porting and finding the right pipe are pretty expensive things to do trial and error with.
 
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