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Discussion Starter · #1 ·
Hi Everyone,

I'm considering installing the necessary parts from the 300R to my 250 to make it 286cc. I live in Thailand and the parts and labour from Honda are abouut 10'000 baht (300 USD). My question is what does the bike ride like after the conversion? Has anyone here done it? I know I could easily just buy a CBR300R but dont really want to.

How is the gearing, acceleration and fueling? Did you change the exhaust?

Any feedback would be very welcome?
 

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Well your also going to need the balance shaft and up-rated crank bearings, fuel computer etc. etc. buy a 300 save yourself the pain and expense, better still buy the 500, or do the search thing as this has been raised before
 

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Discussion Starter · #4 ·
Thanks for your reply Lemmy99. I am aware of what parts are needed as I went to the Honda dealer for the advice and prices. What I really want to know is what the bike is like AFTER the upgrade.

I did do a search but couldn't find any post that answered the question and yes I could buy a 300 but thats more expensive. Paying a Honda trained mechanic to do the work for 300 USD and a couple of days labour is hardly a pain.

As anyone done it yet? and what are their thoughts I may just go ahead and do it, just doin a liitle research beforehand.
 

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I think I've read somewhere here from someone who test rode the 300 when it came out that it felt like a 250 with a sport exhaust system.
Maybe you should ask people who switched from the 250 to the 300. Shisoshin has owned both and could probably give you some feedback. You could also check the CBR 300 forum for people who have moved from 250 to 286cc. I don't believe however that the difference in cc is worth the price. We're talking just 5 hp here IIRC.
 

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Same as a 250 with a slip on and fuel controller basically. Besides, there's a lot more to it than just a few parts, and you'll need a 300 ECU.

Most cost effective would be finding a used 300r engine and 300r ECU, as the O2 sensor is no longer located in the head as in the 250.
 

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SmBkRdrd rebuilt my engine to a 286, leaving the clutch and transmission parts from the 250. I also put on a PowerCommander V from JetTune.com with a custom map. (Too many other mods to mention, but those are the ones that would be relevant for you.) There is a definite improvement in torque, pulling well from mid-range RPMs. There's also a noticeable improvement in HP / top end speed (although not as noticeable as the torque improvements). I race the bike, and am able to keep up to EX250s, EX300s, R3s (and some RC390s, if the rider isn't better than me).


Other than the engine, the CBR300 and CBR250 are almost identical bikes. They handle better than any competitor, and with the extra torque it is a fantastic all around bike.


For as cheap as you can get it done, I would highly recommend it.
 

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Discussion Starter · #9 ·
Thanks, yes I hope to add an aftermarket fuel controller and full system also, maybe a termignoni. I don't race, mainly commuting with some weekend fun but the bike is also my hobby and I don't ever plan on selling it.
 

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Hello Everyone... I have cbr250r 2014. What parts exactly need to get this job done.. Correct me if i am wrong
1. 300 crankshaft
2. 300 Balancershaft & balancer gears
3. 300 piston & rings
4. 300 ecu( is it compatible with 2014 cbr250 wiring)
 

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Honda: INNOVA125i(2010); CBR250R(2013)
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Hello Everyone... I have cbr250r 2014. What parts exactly need to get this job done.. Correct me if i am wrong
1. 300 crankshaft
2. 300 Balancershaft & balancer gears
3. 300 piston & rings
4. 300 ecu( is it compatible with 2014 cbr250 wiring)
And what about a reinforced clutch that is adapted to the improved torque? ... is a never-ending story.
A lot of the reviews I read claimed that: "It Not worth the effort"
But if you need a general overhaul of the engine anyway, I would settle for Overe Sized Piston And Rings Set that fit to 250, and let a professional Drill And Honing an Over Sized cylinder(Maybe just Honing is enough, and it can be done by yourself).
A simple NEW exhaust without a catalytic converter, if your catalytic converter is already clogged, this too will give you a noticeable increase in power with no effort and almost no financial expense.
 

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I’m seriously looking at purchasing the JE piston, and boring the cylinder out to 83mm. That would be way easier for more displacement than swapping for the longer stroke… but not as easy as swapping the motor as a unit.
 

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Yeah, you can swap engines in less than 2-4 hrs. Instant power boost without waiting for machine-shop work. And no need to get messy and dirty cracking open your engine!
 
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