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So... do you think we will see some Big Bore Kits in the near future?

I'd love to see an increase in the displacement and would do it in a heartbeat.
 

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So... do you think we will see some Big Bore Kits in the near future?

I'd love to see an increase in the displacement and would do it in a heartbeat.
The CBR250R's balance shaft wasn't designed to quell vibration with a larger piston. It would likely be more vibration prone. A big bore will increase torque, but will probably only marginally increase horsepower. Based on my experience having sampled an Athena kitted 166cc big bore Honda CBR125R - the bike had tons more torque, and could cruise easily at a higher topspeed - this part was great. But the bike showed much more vibration in the upper rev range to the point where I was concerned that the bike might vibrate apart (I never came close to bringing it to redline for this reason). As a result, the kit really mellowed the bike out - I felt I had to ride it like a low redline, high torque, V-twin cruiser which took something away from the high revving nature of the bike and robbed it of its stock character. Based on this experience, I felt the roughness just wasn't worth the additional power and torque to me. Either way - this would be a concern for me.

Mike
 

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The CBR250R's balance shaft wasn't designed to quell vibration with a larger piston. It would likely be more vibration prone. A big bore will increase torque, but will probably only marginally increase horsepower. Based on my experience having sampled an Athena kitted 166cc big bore Honda CBR125R - the bike had tons more torque, and could cruise easily at a higher topspeed - this part was great. But the bike showed much more vibration in the upper rev range to the point where I was concerned that the bike might vibrate apart (I never came close to bringing it to redline for this reason). As a result, the kit really mellowed the bike out - I felt I had to ride it like a low redline, high torque, V-twin cruiser which took something away from the high revving nature of the bike and robbed it of its stock character. Based on this experience, I felt the roughness just wasn't worth the additional power and torque to me. Either way - this would be a concern for me.

Mike
Now if the material the stock piston is made of is heavier then aluminum they could potentially make it the same weight. I guess we will have to wait and see.
 

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@matt
DYNAMICS OF MACHINERY ! BALANCING THEORY

A single cylinder can be balanced primarly using counterweights,but the secondary balancing cant be achieved,and hence an unbalance exists

a twin cylinder engine can be balanced fully.same for
v,w,h engines
 

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this topic came up alot during my scooter riding days. People starting on 50cc bikes quickly find them lacking and dangerous in anything but stop and go traffic. So a malossi 78.8cc kit is installed and its great. much more torque but still no increase in top end. More upgrades are needed like final gearing and in the end it comes down to it is cheaper and better in the long run to just get a bigger bike.

I went thru that whole upgrade-itis thing. 50cc>78.8cc kit to a 150cc bike to a 460cc bike and now the CBR. Now trying to decide if i want to keep the 250 for another season or get a new 650cc sport tourer for 2013.
 

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CBR250R 305cc Big Bore Kit

Sendler had posted about this in the CBR500 thread, but I figured it would be useful to have it in this thread for obvious reasons. I'm thinking kit + fuel controller + exhaust + dyno tuning = a lot of money to spend on a $4k 250cc bike. The question is would it be worth it? Anyone have thoughts?
my whole reason for buying mine was the great gas mileage,
i think mine looks faster than it could ever go:)
 

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in indonesia one of the seller have this 305cc boreup kit for cbr250r mc41. it about 3,5million rupiah (about $365)

 

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In my youth the reason for a big bore kit was to flaunt the learner laws. Yes officer it is a 50. look it says so on the sticker. Nowadays the size is stamped on the liner casting.
 

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There is other ways to make power than a big bore.
Yup, and cheaper. As a commuter, I can't get over 75mph without looking around for police lights, so I went with lower gearing instead. Guess what speed peak power hits at now. It starts with "seventy" and rhymes with... "seventy-five miles per hour". The rear wheel torque is night and day difference over stock. Immediate pull in all 6 gears at any speed. No pussin' around. For a BBK, I'd think you need not only the kit, but a big valve header, high-flow pipe, fuel controller, and a custom map from a dyno, You could spend over 25% of the cost of the bike modding it when there are used 600 supersports out there that would still mop the floor with a maxed out 250... stock.
 

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... For a BBK, I'd think you need not only the kit, but a big valve header, high-flow pipe, fuel controller, and a custom map from a dyno...
To maximize the effect of a big bore kit, I wonder if a larger throttle body would be desirable. Maybe the 305 cc displacement is within the stock throttle body air flow capability to feed the motor? Back in the day, many big bore kits included a larger carb, to flow more air/fuel mixture.
 

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Perhaps. And I'm not the most educated guy in the world on the matter, but I'm under the impression the displacement increase will add power on the bottom end, but will need to breathe better to get equal gains up top because of it. I like the idea of having the BBK option in theory, but am skeptical it may become a slippery slope and money pit.
 

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I knew guys who would throw huge amounts of money into two stroke snowmobile engines, just to gain a few horse power from a motor already pushing 100 hp. Guess they had mad money.
 

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You could spend over 25% of the cost of the bike modding it when there are used 600 supersports out there that would still mop the floor with a maxed out 250... stock.
true, if you live in the West (i used to have a VFR750, bought it for $1,000). here in India, however, any affordable used bike on the market is gonna be 150cc max. if it's as old as my VFR was, probably more like 100cc.

the choice is modding the CBR or buying a brand new KTM 390. even if i got lucky and was able to sell my used CBR (which is 2 years old now), i probably could only recoup half its value, and then still have a couple grand + change to make up for the new Duke. that, and i trust my 2 yr old Honda over a new KTM. (and the Duke looks like it was designed by a 15 year old; i would honestly fool like a tool driving around on that thing, now that i'm in my thirties).

if i want more performance, it is cheaper to buy it by updating my current bike (and meanwhile making it how i want it) than simply buying another stock bike that ISN'T what i want.

so i'm spending 25-50% of my bike to "rebuy" MY bike, that i like, with more power, instead of spending 200% of my bike to buy a new KTM that i'm not really all that excited for.

here's what i'm looking at: Page 1
 
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